Science.gov

Sample records for acoustic noise levels

  1. Effects of voice style, noise level, and acoustic feedback on objective and subjective voice evaluations

    PubMed Central

    Bottalico, Pasquale; Graetzer, Simone; Hunter, Eric J.

    2015-01-01

    Speakers adjust their vocal effort when communicating in different room acoustic and noise conditions and when instructed to speak at different volumes. The present paper reports on the effects of voice style, noise level, and acoustic feedback on vocal effort, evaluated as sound pressure level, and self-reported vocal fatigue, comfort, and control. Speakers increased their level in the presence of babble and when instructed to talk in a loud style, and lowered it when acoustic feedback was increased and when talking in a soft style. Self-reported responses indicated a preference for the normal style without babble noise. PMID:26723357

  2. A survey of acoustic conditions and noise levels in secondary school classrooms in England.

    PubMed

    Shield, Bridget; Conetta, Robert; Dockrell, Julie; Connolly, Daniel; Cox, Trevor; Mydlarz, Charles

    2015-01-01

    An acoustic survey of secondary schools in England has been undertaken. Room acoustic parameters and background noise levels were measured in 185 unoccupied spaces in 13 schools to provide information on the typical acoustic environment of secondary schools. The unoccupied acoustic and noise data were correlated with various physical characteristics of the spaces. Room height and the amount of glazing were related to the unoccupied reverberation time and therefore need to be controlled to reduce reverberation to suitable levels for teaching and learning. Further analysis of the unoccupied data showed that the introduction of legislation relating to school acoustics in England and Wales in 2003 approximately doubled the number of school spaces complying with current standards. Noise levels were also measured during 274 lessons to examine typical levels generated during teaching activities in secondary schools and to investigate the influence of acoustic design on working noise levels in the classroom. Comparison of unoccupied and occupied data showed that unoccupied acoustic conditions affect the noise levels occurring during lessons. They were also related to the time spent in disruption to the lessons (e.g., students talking or shouting) and so may also have an impact upon student behavior in the classroom.

  3. School cafeteria noise-The impact of room acoustics and speech intelligibility on children's voice levels

    NASA Astrophysics Data System (ADS)

    Bridger, Joseph F.

    2002-05-01

    The impact of room acoustics and speech intelligibility conditions of different school cafeterias on the voice levels of children is examined. Methods of evaluating cafeteria designs and predicting noise levels are discussed. Children are shown to modify their voice levels with changes in speech intelligibility like adults. Reverberation and signal to noise ratio are the important acoustical factors affecting speech intelligibility. Children have much more difficulty than adults in conditions where noise and reverberation are present. To evaluate the relationship of voice level and speech intelligibility, a database of real sound levels and room acoustics data was generated from measurements and data recorded during visits to a variety of existing cafeterias under different occupancy conditions. The effects of speech intelligibility and room acoustics on childrens voice levels are demonstrated. A new method is presented for predicting speech intelligibility conditions and resulting noise levels for the design of new cafeterias and renovation of existing facilities. Measurements are provided for an existing school cafeteria before and after new room acoustics treatments were added. This will be helpful for acousticians, architects, school systems, regulatory agencies, and Parent Teacher Associations to create less noisy cafeteria environments.

  4. Load influence on gear noise. [mathematical model for determining acoustic pressure level as function of load

    NASA Technical Reports Server (NTRS)

    Merticaru, V.

    1974-01-01

    An original mathematical model is proposed to derive equations for calculation of gear noise. These equations permit the acoustic pressure level to be determined as a function of load. Application of this method to three parallel gears is reported. The logical calculation scheme is given, as well as the results obtained.

  5. Influences of environmental noise level and respiration rate on the accuracy of acoustic respiration rate monitoring.

    PubMed

    Yabuki, Shizuha; Toyama, Hiroaki; Takei, Yusuke; Wagatsuma, Toshihiro; Yabuki, Hiroshi; Yamauchi, Masanori

    2017-02-07

    We tested the hypothesis that the environmental noise generated by a forced-air warming system reduces the monitoring accuracy of acoustic respiration rate (RRa). Noise levels were adjusted to 45-55, 56-65, 66-75, and 76-85 dB. Healthy participants breathed at set respiration rates (RRset) of 6, 12, and 30/min. Under each noise level at each RRset, the respiration rates by manual counting (RRm) and RRa were recorded. Any appearance of the alarm display on the RRa monitor was also recorded. Each RRm of all participants agreed with each RRset at each noise level. At 45-55 dB noise, the RRa of 13, 17, and 17 participants agreed with RRset of 6, 12, and 30/min, respectively. The RRa of 14, 17, and 16 participants at 56-65 dB noise, agreed with RRset of 6, 12, and 30/min, respectively. At 66-75 dB noise, the RRa of 9, 15, and 16 participants agreed with RRset of 6, 12, and 30/min, respectively. The RRa of one, nine, and nine participants at 76-85 dB noise agreed with RRset of 6, 12, and 30/min, respectively, which was significantly less than the other noise levels (P < 0.05). Overall, 72.9% of alarm displays highlighted incorrect values of RRa. In a noisy situation involving the operation of a forced-air warming system, the acoustic respiration monitoring should be used carefully especially in patients with a low respiration rate.

  6. Baseline acoustic levels of the NASA Active Noise Control Fan rig

    NASA Technical Reports Server (NTRS)

    Sutliff, Daniel L.; Heidelberg, Laurence J.; Elliott, David M.; Nallasamy, M.

    1996-01-01

    Extensive measurements of the spinning acoustic mode structure in the NASA 48 inch Active Noise Control Fan (ANCF) test rig have been taken. A continuously rotating microphone rake system with a least-squares data reduction technique was employed to measure these modes in the inlet and exhaust. Farfield directivity patterns in an anechoic environment were also measured at matched corrected rotor speeds. Several vane counts and spacings were tested over a range of rotor speeds. The Eversman finite element radiation code was run with the measured in-duct modes as input and the computed farfield results were compared to the experimentally measured directivity pattern. The experimental data show that inlet spinning mode measurements can be made very accurately. Exhaust mode measurements may have wake interference, but the least-squares reduction does a good job of rejecting the non-acoustic pressure. The Eversman radiation code accurately extrapolates the farfield levels and directivity pattern when all in-duct modes are included.

  7. A seismic field test with a Low-level Acoustic Combustion Source and Pseudo-Noise codes

    NASA Astrophysics Data System (ADS)

    Askeland, Bjørn; Ruud, Bent Ole; Hobæk, Halvor; Mjelde, Rolf

    2009-01-01

    The Low-level Acoustic Combustion Source (LACS) which can fire its pulses at a high rate, has been tested successfully as a seismic marine source on shallow ice-age sediments in Byfjorden at Bergen, Norway. Pseudo-Noise pulsed signals with spiky autocorrelation functions were used to detect the sediments. Each transmitted sequence lasted 10 s and contained 43 pulses. While correlation gave a blurry result, deconvolution between the near-field recordings and the streamer recordings gave a clear seismic section. Compared to the section acquired with single air-gun shots along the same profile, the LACS gave a more clear presentation of the sediments and basement.

  8. Acoustic Noise Levels of Dental Equipments and Its Association with Fear and Annoyance Levels among Patients Attending Different Dental Clinic Setups in Jaipur, India

    PubMed Central

    Ganta, Shravani; Nagaraj, Anup; Pareek, Sonia; Atri, Mansi; Singh, Kushpal; Sidiq, Mohsin

    2014-01-01

    Background: Noise is a source of pervasive occupational hazard for practicing dentists and the patients. The sources of dental sounds by various dental equipments can pose as a potential hazard to hearing system and add to the annoyance levels of the patients. The aim of the study was to analyze the noise levels from various equipments and evaluate the effect of acoustic noise stimulus on dental fear and annoyance levels among patients attending different dental clinic setups in Jaipur, India. Methodology: The sampling frame comprised of 180 patients, which included 90 patients attending 10 different private clinics and 90 patients attending a Dental College in Jaipur. The levels of Acoustic Noise Stimulus originating from different equipments were determined using a precision sound level meter/decibulometer. Dental fear among patients was measured using Dental Fear Scale (DFS). Results: Statistical analysis was performed using chi square test and unpaired t-test. The mean background noise levels were found to be maximum in the pre-clinical setup/ laboratory areas (69.23+2.20). Females and the patients attending dental college setup encountered more fear on seeing the drill as compared to the patients attending private clinics (p<0.001). Conclusion: The sources of dental sounds can pose as a potential hazard to hearing system. It was analyzed that the environment in the clinics can directly have an effect on the fear and annoyance levels of patients. Hence it is necessary control the noise from various dental equipments to reduce the fear of patients from visiting a dental clinic. PMID:24959512

  9. Acoustic noise during functional magnetic resonance imaging.

    PubMed

    Ravicz, M E; Melcher, J R; Kiang, N Y

    2000-10-01

    Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For studies of the auditory system, acoustic noise generated during fMRI can interfere with assessments of this activation by introducing uncontrolled extraneous sounds. As a first step toward reducing the noise during fMRI, this paper describes the temporal and spectral characteristics of the noise present under typical fMRI study conditions for two imagers with different static magnetic field strengths. Peak noise levels were 123 and 138 dB re 20 microPa in a 1.5-tesla (T) and a 3-T imager, respectively. The noise spectrum (calculated over a 10-ms window coinciding with the highest-amplitude noise) showed a prominent maximum at 1 kHz for the 1.5-T imager (115 dB SPL) and at 1.4 kHz for the 3-T imager (131 dB SPL). The frequency content and timing of the most intense noise components indicated that the noise was primarily attributable to the readout gradients in the imaging pulse sequence. The noise persisted above background levels for 300-500 ms after gradient activity ceased, indicating that resonating structures in the imager or noise reverberating in the imager room were also factors. The gradient noise waveform was highly repeatable. In addition, the coolant pump for the imager's permanent magnet and the room air-handling system were sources of ongoing noise lower in both level and frequency than gradient coil noise. Knowledge of the sources and characteristics of the noise enabled the examination of general approaches to noise control that could be applied to reduce the unwanted noise during fMRI sessions.

  10. Acoustic considerations of flight effects on jet noise suppressor nozzles

    NASA Technical Reports Server (NTRS)

    Vonglahn, U.

    1979-01-01

    The inflight acoustic characteristics of high velocity jet noise suppressor nozzles for supersonic cruise aircraft were reviewed. The inflight effects at the peak noise level were discussed. Both single and inverted velocity profile multistream suppressor nozzles were considered. The importance of static spectral shape on the noise reduction due to inflight effects was stressed.

  11. Acoustic considerations of flight effects on jet noise suppressor nozzles

    NASA Technical Reports Server (NTRS)

    Von Glahn, U.

    1980-01-01

    Insight into the inflight acoustic characteristics of high-velocity jet noise suppressor nozzles for supersonic cruise aircraft (SCA) is provided. Although the suppression of jet noise over the entire range of directivity angles is of interest, the suppression of the peak noise level in the rear quadrant is frequently of the most interest. Consequently, the paper is directed primarily to the inflight effects at the peak noise level. Both single and inverted-velocity-profile multistream suppressor nozzles are considered. The importance of static spectral shape on the noise reduction due to inflight effects is stressed.

  12. Coherent entropy induced and acoustic noise separation in compact nozzles

    NASA Astrophysics Data System (ADS)

    Tao, Wenjie; Schuller, Thierry; Huet, Maxime; Richecoeur, Franck

    2017-04-01

    A method to separate entropy induced noise from an acoustic pressure wave in an harmonically perturbed flow through a nozzle is presented. It is tested on an original experimental setup generating simultaneously acoustic and temperature fluctuations in an air flow that is accelerated by a convergent nozzle. The setup mimics the direct and indirect noise contributions to the acoustic pressure field in a confined combustion chamber by producing synchronized acoustic and temperature fluctuations, without dealing with the complexity of the combustion process. It allows generating temperature fluctuations with amplitude up to 10 K in the frequency range from 10 to 100 Hz. The noise separation technique uses experiments with and without temperature fluctuations to determine the relative level of acoustic and entropy fluctuations in the system and to identify the nozzle response to these forcing waves. It requires multi-point measurements of acoustic pressure and temperature. The separation method is first validated with direct numerical simulations of the nonlinear Euler equations. These simulations are used to investigate the conditions for which the separation technique is valid and yield similar trends as the experiments for the investigated flow operating conditions. The separation method then gives successfully the acoustic reflection coefficient but does not recover the same entropy reflection coefficient as predicted by the compact nozzle theory due to the sensitivity of the method to signal noises in the explored experimental conditions. This methodology provides a framework for experimental investigation of direct and indirect combustion noises originating from synchronized perturbations.

  13. Ambient noise analysis of underwater acoustic data

    NASA Astrophysics Data System (ADS)

    Snyder, Mark A.; Orlin, Pete; Schulte, Annette; Newcomb, Joal

    2003-04-01

    The Littoral Acoustic Demonstration Center (LADC) deployed three Environmental Acoustic Recording System (EARS) buoys in the northern Gulf of Mexico during the summers of 2001 and 2002. The buoys recorded frequencies up to 5859 Hz continuously for 36 days in 2001 and for 72 days in 2002. The acoustic signals recorded include sperm whale vocalizations, seismic airguns, and shipping traffic. The variability of the ambient noise is analyzed using spectrograms, time series, and statistical measurements. Variations in ambient noise before, during, and after tropical storm/hurricane passage are also investigated.

  14. Acoustic Imaging of Combustion Noise

    NASA Technical Reports Server (NTRS)

    Ramohalli, K. N.; Seshan, P. K.

    1984-01-01

    Elliposidal acoustic mirror used to measure sound emitted at discrete points in burning turbulent jets. Mirror deemphasizes sources close to target source and excludes sources far from target. At acoustic frequency of 20 kHz, mirror resolves sound from region 1.25 cm wide. Currently used by NASA for research on jet flames. Produces clearly identifiable and measurable variation of acoustic spectral intensities along length of flame. Utilized in variety of monitoring or control systems involving flames or other reacting flows.

  15. Cardiorespiratory Responses to Acoustic Noise in Belugas.

    PubMed

    Lyamin, Oleg I; Korneva, Svetlana M; Rozhnov, Viatcheslav V; Mukhametov, Lev M

    2016-01-01

    To date, most research on the adverse effects of anthropogenic noise on marine mammals has focused on auditory and behavioral responses. Other responses have received little attention and are often ignored. In this study, the effect of acoustic noise on heart rate was examined in captive belugas. The data suggest that (1) heart rate can be used as a measure of physiological response (including stress) to noise in belugas and other cetaceans, (2) cardiac response is influenced by parameters of noise and adaptation to repeated exposure, and (3) cetacean calves are more vulnerable to the adverse effect of noise than adults.

  16. Environmental noise-a challenge for an acoustical engineer

    NASA Astrophysics Data System (ADS)

    Genuit, Klaus

    2003-10-01

    People live in a landscape full of noises which are composed of both natural environmental noises and technically created sounds. Regarding environmental noise, more and more people feel heavily annoyed by noises. Noise is defined as an audible sound which either disturbs the silence or an intentional sound listening or leads to annoyance. Thus, it is clearly defined that the assignment of noise cannot be reduced to simple determining objective parameters such as the A-weighted sound pressure level or the equivalent continuous sound pressure level. The question of whether a sound is judged as noise can only be made after the transformation from the sound event into an auditory event has been accomplished. The evaluation of noise depends on the physical characteristics of the sound event, on the psycho-acoustical features of the human ear, as well as on the psychological aspects of man. For the acoustical design of environmental noise and in order to create a better soundscape the acoustical engineer has to consider these aspects. That means a specific challenge for the sound engineering.

  17. Active-passive gradient shielding for MRI acoustic noise reduction.

    PubMed

    Edelstein, William A; Kidane, Tesfaye K; Taracila, Victor; Baig, Tanvir N; Eagan, Timothy P; Cheng, Yu-Chung N; Brown, Robert W; Mallick, John A

    2005-05-01

    An important source of MRI acoustic noise-magnet cryostat warm-bore vibrations caused by eddy-current-induced forces-can be mitigated by a passive metal shield mounted on the outside of a vibration-isolated, vacuum-enclosed shielded gradient set. Finite-element (FE) calculations for a z-gradient indicate that a 2-mm-thick Cu layer wrapped on the gradient assembly can decrease mechanical power deposition in the warm bore and reduce warm-bore acoustic noise production by about 25 dB. Eliminating the conducting warm bore and other magnet parts as significant acoustic noise sources could lead to the development of truly quiet, fully functioning MRI systems with noise levels below 70 dB.

  18. Acoustic noise reduction in a 4 T MRI scanner.

    PubMed

    Mechefske, Chris K; Geris, Ryan; Gati, Joseph S; Rutt, Brian K

    2002-01-01

    High-field, high-speed magnetic resonance imaging (MRI) can generate high levels of noise. There is ongoing concern in the medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 T MRI scanner under a variety of conditions. These measurement results show: (1) that noise levels can be significantly reduced through the use of an appropriately designed passive acoustic liner; and (2) the true noise levels that are experienced by patients during echo planar imaging.

  19. The Acoustic Analogy and Alternative Theories for Jet Noise Prediction

    NASA Technical Reports Server (NTRS)

    Morris, Philip J.; Farassat, F.

    2002-01-01

    This paper describes several methods for the prediction of jet noise. All but one of the noise prediction schemes are based on Lighthill's or Lilley's acoustic analogy while the other is the jet noise generation model recently proposed by Tam and Auriault. In all the approaches some assumptions must be made concerning the statistical properties of the turbulent sources. In each case the characteristic scales of the turbulence are obtained from a solution of the Reynolds-averaged Navier Stokes equation using a k - epsilon turbulence model. It is shown that, for the same level of empiricism, Tam and Auriault's model yields better agreement with experimental noise measurements than the acoustic analogy. It is then shown that this result is not because of some fundamental flaw in the acoustic analogy approach: but, is associated with the assumptions made in the approximation of the turbulent source statistics. If consistent assumptions are made, both the acoustic analogy and Tam and Auriault's model yield identical noise predictions. The paper concludes with a proposal for an acoustic analogy that provides a clearer identification of the equivalent source mechanisms and a discussion of noise prediction issues that remain to be resolved.

  20. Acoustic Analogy and Alternative Theories for Jet Noise Prediction

    NASA Technical Reports Server (NTRS)

    Morris, Philip J.; Farassat, F.

    2002-01-01

    Several methods for the prediction of jet noise are described. All but one of the noise prediction schemes are based on Lighthill's or Lilley's acoustic analogy, whereas the other is the jet noise generation model recently proposed by Tam and Auriault. In all of the approaches, some assumptions must be made concerning the statistical properties of the turbulent sources. In each case the characteristic scales of the turbulence are obtained from a solution of the Reynolds-averaged Navier-Stokes equation using a kappa-sigma turbulence model. It is shown that, for the same level of empiricism, Tam and Auriault's model yields better agreement with experimental noise measurements than the acoustic analogy. It is then shown that this result is not because of some fundamental flaw in the acoustic analogy approach, but instead is associated with the assumptions made in the approximation of the turbulent source statistics. If consistent assumptions are made, both the acoustic analogy and Tam and Auriault's model yield identical noise predictions. In conclusion, a proposal is presented for an acoustic analogy that provides a clearer identification of the equivalent source mechanisms, as is a discussion of noise prediction issues that remain to be resolved.

  1. The Acoustic Analogy and Alternative Theories for Jet Noise Prediction

    NASA Technical Reports Server (NTRS)

    Morris, Philip J.; Farassat, F.; Morris, Philip J.

    2002-01-01

    This paper describes several methods for the prediction of jet noise. All but one of the noise prediction schemes are based on Lighthill's or Lilley's acoustic analogy while the other is the jet noise generation model recently proposed by Tam and Auriault. In all the approaches some assumptions must be made concerning the statistical properties of the turbulent sources. In each case the characteristic scales of the turbulence are obtained from a solution of the Reynolds-averaged Navier Stokes equation using a k-epsilon turbulence model. It is shown that, for the same level of empiricism, Tam and Auriault's model yields better agreement with experimental noise measurements than the acoustic analogy. It is then shown that this result is not because of some fundamental flaw in the acoustic analogy approach: but, is associated with the assumptions made in the approximation of the turbulent source statistics. If consistent assumptions are made, both the acoustic analogy and Tam and Auriault's model yield identical noise predictions. The paper concludes with a proposal for an acoustic analogy that provides a clearer identification of the equivalent source mechanisms and a discussion of noise prediction issues that remain to be resolved.

  2. Program in acoustics. [aeroacoustics, aircraft noise, and noise suppression

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Relevant research projects conducted by faculty and graduate students in the general area of aeroacoustics to further the understanding of noise generation by aircraft and to aid in the development of practical methods for noise suppression are listed. Special activities summarized relate to the nonlinear acoustic wave theory and its application to several cases including that of the acoustic source located at the throat of a near-sonic duct, a computer program developed to compute the nonlinear wave theory, and a parabolic approximation for propagation of sounding in moving stratified media.

  3. Ocean Basin Impact of Ambient Noise on Marine Mammal Detectability, Distribution, and Acoustic Communication

    DTIC Science & Technology

    2015-07-06

    Technical Report 4. TITLE AND SUBTITLE Ocean Basin Impact of Ambient Noise on Marine Mammal Distribution, and Acoustic Communication 3. DATES...ultimate goal of this research is to enhance the understanding of global ocean noise and how variability in sound level impacts marine mammal acoustic...it relates to marine mammal active acoustic space and acoustic communication. This work increases the spatial range and time scale of prior

  4. [Evaluation of acoustic effectiveness of personnel protectors from extra-aural exposure to aviation noise].

    PubMed

    Dragan, S P; Soldatov, S K; Bogomolov, A V; Drozdov, S V; Poliakov, N M

    2013-01-01

    Purpose of the investigation was to validate testing acoustic effectiveness of a personnel vest-like protector (PP) from extra-aural exposure to aviation noise. Levels of aviation noise for PP testing were determined through calculation. Vest effectiveness in protecting from acoustic vibration generated by high-intensity aviation noise was evaluated both in laboratory and field tests. For comparison analysis, PP was also tested with a dummy exposed on a special tester, i.e. acoustic interferometer.

  5. Effects of acoustic noise on the auditory nerve compound action potentials evoked by electric pulse trains.

    PubMed

    Nourski, Kirill V; Abbas, Paul J; Miller, Charles A; Robinson, Barbara K; Jeng, Fuh-Cherng

    2005-04-01

    This study investigated the effects of acoustic noise on the auditory nerve compound action potentials in response to electric pulse trains. Subjects were adult guinea pigs, implanted with a minimally invasive electrode to preserve acoustic sensitivity. Electrically evoked compound action potentials (ECAP) were recorded from the auditory nerve trunk in response to electric pulse trains both during and after the presentation of acoustic white noise. Simultaneously presented acoustic noise produced a decrease in ECAP amplitude. The effect of the acoustic masker on the electric probe was greatest at the onset of the acoustic stimulus and it was followed by a partial recovery of the ECAP amplitude. Following cessation of the acoustic noise, ECAP amplitude recovered over a period of approximately 100-200 ms. The effects of the acoustic noise were more prominent at lower electric pulse rates (interpulse intervals of 3 ms and higher). At higher pulse rates, the ECAP adaptation to the electric pulse train alone was larger and the acoustic noise, when presented, produced little additional effect. The observed effects of noise on ECAP were the greatest at high electric stimulus levels and, for a particular electric stimulus level, at high acoustic noise levels.

  6. Are urban noise pollution levels decreasing?

    PubMed

    Arana, M

    2010-04-01

    The majority of acoustic impact studies developed over the last 50 years have used a similar acoustic parameter (L(eq), L(dn)) but the noise mapping methodology has been very uneven. The selection of the measurement points, the measurement periods, or the evaluation indices have not followed a unique criterion. Therefore, it is not possible to compare the sound pollution levels between different cities from those studies, at least in a rigorous sense. Even more, different studies carried out in the same city by different researchers during different years and using different methodologies are not conclusive whether the acoustic pollution increases or decreases. The present paper shows results, with statistical significance, about the evolution of the acoustic pollution obtained for two Spanish cities, Pamplona and Madrid. In both cases, it can be concluded that noise pollution decreases over time (P<0.01).

  7. Underwater noise levels in UK waters

    NASA Astrophysics Data System (ADS)

    Merchant, Nathan D.; Brookes, Kate L.; Faulkner, Rebecca C.; Bicknell, Anthony W. J.; Godley, Brendan J.; Witt, Matthew J.

    2016-11-01

    Underwater noise from human activities appears to be rising, with ramifications for acoustically sensitive marine organisms and the functioning of marine ecosystems. Policymakers are beginning to address the risk of ecological impact, but are constrained by a lack of data on current and historic noise levels. Here, we present the first nationally coordinated effort to quantify underwater noise levels, in support of UK policy objectives under the EU Marine Strategy Framework Directive (MSFD). Field measurements were made during 2013–2014 at twelve sites around the UK. Median noise levels ranged from 81.5–95.5 dB re 1 μPa for one-third octave bands from 63–500 Hz. Noise exposure varied considerably, with little anthropogenic influence at the Celtic Sea site, to several North Sea sites with persistent vessel noise. Comparison of acoustic metrics found that the RMS level (conventionally used to represent the mean) was highly skewed by outliers, exceeding the 97th percentile at some frequencies. We conclude that environmental indicators of anthropogenic noise should instead use percentiles, to ensure statistical robustness. Power analysis indicated that at least three decades of continuous monitoring would be required to detect trends of similar magnitude to historic rises in noise levels observed in the Northeast Pacific.

  8. Underwater noise levels in UK waters.

    PubMed

    Merchant, Nathan D; Brookes, Kate L; Faulkner, Rebecca C; Bicknell, Anthony W J; Godley, Brendan J; Witt, Matthew J

    2016-11-10

    Underwater noise from human activities appears to be rising, with ramifications for acoustically sensitive marine organisms and the functioning of marine ecosystems. Policymakers are beginning to address the risk of ecological impact, but are constrained by a lack of data on current and historic noise levels. Here, we present the first nationally coordinated effort to quantify underwater noise levels, in support of UK policy objectives under the EU Marine Strategy Framework Directive (MSFD). Field measurements were made during 2013-2014 at twelve sites around the UK. Median noise levels ranged from 81.5-95.5 dB re 1 μPa for one-third octave bands from 63-500 Hz. Noise exposure varied considerably, with little anthropogenic influence at the Celtic Sea site, to several North Sea sites with persistent vessel noise. Comparison of acoustic metrics found that the RMS level (conventionally used to represent the mean) was highly skewed by outliers, exceeding the 97(th) percentile at some frequencies. We conclude that environmental indicators of anthropogenic noise should instead use percentiles, to ensure statistical robustness. Power analysis indicated that at least three decades of continuous monitoring would be required to detect trends of similar magnitude to historic rises in noise levels observed in the Northeast Pacific.

  9. Underwater noise levels in UK waters

    PubMed Central

    Merchant, Nathan D.; Brookes, Kate L.; Faulkner, Rebecca C.; Bicknell, Anthony W. J.; Godley, Brendan J.; Witt, Matthew J.

    2016-01-01

    Underwater noise from human activities appears to be rising, with ramifications for acoustically sensitive marine organisms and the functioning of marine ecosystems. Policymakers are beginning to address the risk of ecological impact, but are constrained by a lack of data on current and historic noise levels. Here, we present the first nationally coordinated effort to quantify underwater noise levels, in support of UK policy objectives under the EU Marine Strategy Framework Directive (MSFD). Field measurements were made during 2013–2014 at twelve sites around the UK. Median noise levels ranged from 81.5–95.5 dB re 1 μPa for one-third octave bands from 63–500 Hz. Noise exposure varied considerably, with little anthropogenic influence at the Celtic Sea site, to several North Sea sites with persistent vessel noise. Comparison of acoustic metrics found that the RMS level (conventionally used to represent the mean) was highly skewed by outliers, exceeding the 97th percentile at some frequencies. We conclude that environmental indicators of anthropogenic noise should instead use percentiles, to ensure statistical robustness. Power analysis indicated that at least three decades of continuous monitoring would be required to detect trends of similar magnitude to historic rises in noise levels observed in the Northeast Pacific. PMID:27830837

  10. Measuring Acoustic Noise around Kahoolawe Island.

    DTIC Science & Technology

    1981-10-01

    NAVAL OCEAN SYSTEMS CENTER SAN DIEGO, CALIFORNIA 92152 C y 2 .V ANAVAL OCEAN SYSTEMS CENTER, SAN DIEGO, CA 92152 AN ACTIV IT Y OF THE NAVAL... Ocean Systems Center (NOSC), Code 512, on NSAP Project TH-1 -80, "Measurement of Acoustic Noise Around Kahoolawe". CDR J. W. Carlmark, USN, COMTHIRDFLT N...Bioacoustics & Bionics Division Biosciences Department ,or -.. .- ?---1 1 : ’" " "’ .... .-j UNCLASSIFIED SECURITY CLASSIFICATION OF THIS PAGE (When Data

  11. MRI acoustic noise: sound pressure and frequency analysis.

    PubMed

    Counter, S A; Olofsson, A; Grahn, H F; Borg, E

    1997-01-01

    The large gradient coils used in MRI generate, simultaneously with the pulsed radiofrequency (RF) wave, acoustic noise of high intensity that has raised concern regarding hearing safety. The sound pressure levels (SPLs) and power spectra of MRI acoustic noise were measured at the position of the human head in the isocenter of five MRI systems and with 10 different pulse sequences used in clinical MR scanning. Each protocol, including magnetization-prepared rapid gradient echo (MP-RAGE; 113 dB SPL linear), fast gradient echo turbo (114 dB SPL linear), and spin echo T1/2 mm (117 dB SPL linear), was found to have the high SPLs, rapid pulse rates, amplitude-modulated pulse envelopes, and multipeaked spectra. Since thickness and SPL were inversely related, the T1-weighted images generated more intense acoustic noise than the proton-dense T2-weighted measures. The unfiltered linear peak values provided more accurate measurements of the SPL and spectral content of the MRI acoustic noise than the commonly used dB A-weighted scale, which filters out the predominant low frequency components. Fourier analysis revealed predominantly low frequency energy peaks ranging from .05 to approximately 1 kHz, with a steep high frequency cutoff for each pulse sequence. Ear protectors of known attenuation ratings are recommended for all patients during MRI testing.

  12. Shaping and timing gradient pulses to reduce MRI acoustic noise.

    PubMed

    Segbers, Marcel; Rizzo Sierra, Carlos V; Duifhuis, Hendrikus; Hoogduin, Johannes M

    2010-08-01

    A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an acoustic gradient coil response mainly during the rising and falling edge. In the falling edge, the coil acoustic response presents a 180 degrees phase difference compared to the rising edge. Therefore, by varying the width of the trapezoid and keeping the ramps constant, it is possible to suppress one selected frequency and its higher harmonics. This value is matched to one of the prominent resonance frequencies of the gradient coil system. The idea of cancelling a single frequency is extended to a second frequency, using two successive trapezoid-shaped pulses presented at a selected interval. Overall sound pressure level reduction of 6 and 10 dB is found for the two trapezoid shapes and a single pulse shape, respectively. The acoustically optimized pulse shape proposed is additionally tested in a simulated echo planar imaging readout train, obtaining a sound pressure level reduction of 12 dB for the best case.

  13. Acoustic tests of duct-burning turbofan jet noise simulation

    NASA Technical Reports Server (NTRS)

    Knott, P. R.; Stringas, E. J.; Brausch, J. F.; Staid, P. S.; Heck, P. H.; Latham, D.

    1978-01-01

    The results of a static acoustic and aerodynamic performance, model-scale test program on coannular unsuppressed and multielement fan suppressed nozzle configurations are summarized. The results of the static acoustic tests show a very beneficial interaction effect. When the measured noise levels were compared with the predicted noise levels of two independent but equivalent conical nozzle flow streams, noise reductions for the unsuppressed coannular nozzles were of the order of 10 PNdB; high levels of suppression (8 PNdB) were still maintained even when only a small amount of core stream flow was used. The multielement fan suppressed coannular nozzle tests showed 15 PNdB noise reductions and up to 18 PNdB noise reductions when a treated ejector was added. The static aerodynamic performance tests showed that the unsuppressed coannular plug nozzles obtained gross thrust coefficients of 0.972, with 1.2 to 1.7 percent lower levels for the multielement fan-suppressed coannular flow nozzles. For the first time anywhere, laser velocimeter velocity profile measurements were made on these types of nozzle configurations and with supersonic heated flow conditions. Measurements showed that a very rapid decay in the mean velocity occurs for the nozzle tested.

  14. Noise transmission loss of aircraft panels using acoustic intensity methods

    NASA Technical Reports Server (NTRS)

    Mcgary, M. C.

    1982-01-01

    The two-microphone, cross-spectral, acoustic intensity measurement technique was used to determine the acoustic transmission loss of three different aircraft panels. The study was conducted in the transmission loss apparatus in the Langley aircraft noise reduction laboratory.

  15. Acoustic FMRI noise: linear time-invariant system model.

    PubMed

    Rizzo Sierra, Carlos V; Versluis, Maarten J; Hoogduin, Johannes M; Duifhuis, Hendrikus Diek

    2008-09-01

    Functional magnetic resonance imaging (fMRI) enables sites of brain activation to be localized in human subjects. For auditory system studies, however, the acoustic noise generated by the scanner tends to interfere with the assessments of this activation. Understanding and modeling fMRI acoustic noise is a useful step to its reduction. To study acoustic noise, the MR scanner is modeled as a linear electroacoustical system generating sound pressure signals proportional to the time derivative of the input gradient currents. The transfer function of one MR scanner is determined for two different input specifications: 1) by using the gradient waveform calculated by the scanner software and 2) by using a recording of the gradient current. Up to 4 kHz, the first method is shown as reliable as the second one, and its use is encouraged when direct measurements of gradient currents are not possible. Additionally, the linear order and average damping properties of the gradient coil system are determined by impulse response analysis. Since fMRI is often based on echo planar imaging (EPI) sequences, a useful validation of the transfer function prediction ability can be obtained by calculating the acoustic output for the EPI sequence. We found a predicted sound pressure level (SPL) for the EPI sequence of 104 dB SPL compared to a measured value of 102 dB SPL. As yet, the predicted EPI pressure waveform shows similarity as well as some differences with the directly measured EPI pressure waveform.

  16. Airframe Noise Prediction by Acoustic Analogy: Revisited

    NASA Technical Reports Server (NTRS)

    Farassat, F.; Casper, Jay H.; Tinetti, A.; Dunn, M. H.

    2006-01-01

    The present work follows a recent survey of airframe noise prediction methodologies. In that survey, Lighthill s acoustic analogy was identified as the most prominent analytical basis for current approaches to airframe noise research. Within this approach, a problem is typically modeled with the Ffowcs Williams and Hawkings (FW-H) equation, for which a geometry-independent solution is obtained by means of the use of the free-space Green function (FSGF). Nonetheless, the aeroacoustic literature would suggest some interest in the use of tailored or exact Green s function (EGF) for aerodynamic noise problems involving solid boundaries, in particular, for trailing edge (TE) noise. A study of possible applications of EGF for prediction of broadband noise from turbulent flow over an airfoil surface and the TE is, therefore, the primary topic of the present work. Typically, the applications of EGF in the literature have been limited to TE noise prediction at low Mach numbers assuming that the normal derivative of the pressure vanishes on the airfoil surface. To extend the application of EGF to higher Mach numbers, the uniqueness of the solution of the wave equation when either the Dirichlet or the Neumann boundary condition (BC) is specified on a deformable surface in motion. The solution of Lighthill s equation with either the Dirichlet or the Neumann BC is given for such a surface using EGFs. These solutions involve both surface and volume integrals just like the solution of FW-H equation using FSGF. Insight drawn from this analysis is evoked to discuss the potential application of EGF to broadband noise prediction. It appears that the use of a EGF offers distinct advantages for predicting TE noise of an airfoil when the normal pressure gradient vanishes on the airfoil surface. It is argued that such an approach may also apply to an airfoil in motion. However, for the prediction of broadband noise not directly associated with a trailing edge, the use of EGF does not

  17. Acoustic Characteristics of Sentences Produced in Noise

    DTIC Science & Technology

    1989-09-01

    MONITORING OPOANIZATION REPORT NUMIIIIR( S ) AAMRL-TR-89- 036 1 ao.rNAM OF P1 ORM IN G ORGANIZATION 6 .OFFICE SY B L U , NAME OF MNITORIN G 6ORANIZA7IONary...and aerodynamic characteristics of pharyngeal consonants in Iraqi Arabic," Phonetica, 44, 156-172. 4. Cyphers, D . S ., Kassel, R. H., Kaufman, D . Hd...AAMRL-TR-89-036 AD-A235 344UIl IIIIII 11111111 liii III!l ~ l!l ACOUSTIC CHARACTERISTICS OF SENTENCES PRODUCED IN NOISE Z, S . Bond Thomas J. Moore

  18. Subwavelength acoustic metamaterial panels for underwater noise isolation.

    PubMed

    Hicks, Ashley J; Haberman, Michael R; Wilson, Preston S

    2015-09-01

    Acoustically thin metamaterial underwater noise isolation panels have been developed that provide as much as 16 dB of noise isolation for a panel with a thickness just 160th of the wavelength in the host medium (fresh water) at 2.5 kHz. The panels are composed of thin layers of neoprene rubber and polyoxymethylene containing air-filled voids. The level of isolation provided by the panels is shown to correlate positively with the volume fraction of air voids within the panel.

  19. The Dornier 328 Acoustic Test Cell (ATC) for interior noise tests and selected test results

    NASA Technical Reports Server (NTRS)

    Hackstein, H. Josef; Borchers, Ingo U.; Renger, Klaus; Vogt, Konrad

    1992-01-01

    To perform acoustic studies for achieving low noise levels for the Dornier 328, an acoustic test cell (ATC) of the Dornier 328 has been built. The ATC consists of a fuselage section, a realistic fuselage suspension system, and three exterior noise simulation rings. A complex digital 60 channel computer/amplifier noise generation system as well as multichannel digital data acquisition and evaluation system have been used. The noise control tests started with vibration measurements for supporting acoustic data interpretation. In addition, experiments have been carried out on dynamic vibration absorbers, the most important passive noise reduction measure for low frequency propeller noise. The design and arrangement of the current ATC are presented. Furthermore, exterior noise simulation as well as data acquisition are explained. The most promising results show noise reduction due to synchrophasing and dynamic vibration absorbers.

  20. Acoustics of Jet Surface Interaction - Scrubbing Noise

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas

    2014-01-01

    Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity to the structure or embedded in the airframe. While such integrated systems are intended to shield noise from the community, they also introduce new sources of sound. Sound generation due to interaction of a jet flow past a nearby solid surface is investigated here using the generalized acoustic analogy theory. The analysis applies to the boundary layer noise generated at and near a wall, and excludes the scattered noise component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far field sound as governed by the variable density Pridmore-Brown equation. The propagation Green's function is solved numerically for a high aspect-ratio rectangular jet starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. It is shown the magnitude of the Green's function decreases with increasing source frequency and/or jet temperature. The phase remains constant for a rigid surface, but varies with source location when subject to an impedance type boundary condition. The Green's function in the absence of the surface, and flight effects are also investigated

  1. An Overview of Virtual Acoustic Simulation of Aircraft Flyover Noise

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A.

    2013-01-01

    Methods for testing human subject response to aircraft flyover noise have greatly advanced in recent years as a result of advances in simulation technology. Capabilities have been developed which now allow subjects to be immersed both visually and aurally in a three-dimensional, virtual environment. While suitable for displaying recorded aircraft noise, the true potential is found when synthesizing aircraft flyover noise because it allows the flexibility and freedom to study sounds from aircraft not yet flown. A virtual acoustic simulation method is described which is built upon prediction-based source noise synthesis, engineering-based propagation modeling, and empirically-based receiver modeling. This source-path-receiver paradigm allows complete control over all aspects of flyover auralization. With this capability, it is now possible to assess human response to flyover noise by systematically evaluating source noise reductions within the context of a system level simulation. Examples of auralized flyover noise and movie clips representative of an immersive aircraft flyover environment are made in the presentation.

  2. Effects of acoustic treatment on the interior noise levels of a twin-engine propeller aircraft - Experimental flight results and theoretical predictions

    NASA Technical Reports Server (NTRS)

    Beyer, T. B.; Powell, C. A.; Daniels, E. F.; Pope, L. D.

    1984-01-01

    In-flight noise level measurements were made within two cabin configurations of a general aviation business aircraft. The Fairchild Merlin IVC twin-engine aircraft was tested with bare walls and fiberglass insulation and in an executive trim configuration. Narrow-band and octave format data were subjected to analyses which permitted identification of the blade passage harmonics (BPH). Cabin noise level reductions (insertion losses) due to added insulation varied with position in the cabin, the BPH number, cabin pressure, and engine torque. The measurements were closely predicted using the propeller aircraft interior noise (PAIN) mode.

  3. Prediction of Acoustic Noise in Switched Reluctance Motor Drives

    SciTech Connect

    Lin, CJ; Fahimi, B

    2014-03-01

    Prediction of acoustic noise distribution generated by electric machines has become an integral part of design and control in noise sensitive applications. This paper presents a fast and precise acoustic noise imaging technique for switched reluctance machines (SRMs). This method is based on distribution of radial vibration in the stator frame of the SRM. Radial vibration of the stator frame, at a network of probing points, is computed using input phase current and phase voltage waveforms. Sequentially, the acceleration of the probing network will be expanded to predict full acceleration on the stator frame surface, using which acoustic noise emission caused by the stator can be calculated using the boundary element method.

  4. Acoustic guide for noise-transmission testing of aircraft

    NASA Technical Reports Server (NTRS)

    Vaicaitis, Rimas (Inventor)

    1987-01-01

    Selective testing of aircraft or other vehicular components without requiring disassembly of the vehicle or components was accomplished by using a portable guide apparatus. The device consists of a broadband noise source, a guide to direct the acoustic energy, soft sealing insulation to seal the guide to the noise source and to the vehicle component, and noise measurement microphones, both outside the vehicle at the acoustic guide output and inside the vehicle to receive attenuated sound. By directing acoustic energy only to selected components of a vehicle via the acoustic guide, it is possible to test a specific component, such as a door or window, without picking up extraneous noise which may be transmitted to the vehicle interior through other components or structure. This effect is achieved because no acoustic energy strikes the vehicle exterior except at the selected component. Also, since the test component remains attached to the vehicle, component dynamics with vehicle frame are not altered.

  5. Temporal pattern of acoustic imaging noise asymmetrically modulates activation in the auditory cortex.

    PubMed

    Ranaweera, Ruwan D; Kwon, Minseok; Hu, Shuowen; Tamer, Gregory G; Luh, Wen-Ming; Talavage, Thomas M

    2016-01-01

    This study investigated the hemisphere-specific effects of the temporal pattern of imaging related acoustic noise on auditory cortex activation. Hemodynamic responses (HDRs) to five temporal patterns of imaging noise corresponding to noise generated by unique combinations of imaging volume and effective repetition time (TR), were obtained using a stroboscopic event-related paradigm with extra-long (≥27.5 s) TR to minimize inter-acquisition effects. In addition to confirmation that fMRI responses in auditory cortex do not behave in a linear manner, temporal patterns of imaging noise were found to modulate both the shape and spatial extent of hemodynamic responses, with classically non-auditory areas exhibiting responses to longer duration noise conditions. Hemispheric analysis revealed the right primary auditory cortex to be more sensitive than the left to the presence of imaging related acoustic noise. Right primary auditory cortex responses were significantly larger during all the conditions. This asymmetry of response to imaging related acoustic noise could lead to different baseline activation levels during acquisition schemes using short TR, inducing an observed asymmetry in the responses to an intended acoustic stimulus through limitations of dynamic range, rather than due to differences in neuronal processing of the stimulus. These results emphasize the importance of accounting for the temporal pattern of the acoustic noise when comparing findings across different fMRI studies, especially those involving acoustic stimulation.

  6. Temporal pattern of acoustic imaging noise asymmetrically modulates activation in the auditory cortex

    PubMed Central

    Ranaweera, Ruwan D.; Kwon, Minseok; Hu, Shuowen; Tamer, Gregory G.; Luh, Wen-Ming; Talavage, Thomas M.

    2015-01-01

    This study investigated the hemisphere-specific effects of the temporal pattern of imaging related acoustic noise on auditory cortex activation. Hemodynamic responses (HDRs) to five temporal patterns of imaging noise corresponding to noise generated by unique combinations of imaging volume and effective repetition time (TR), were obtained using a stroboscopic event-related paradigm with extra-long (≥27.5s) TR to minimize inter-acquisition effects. In addition to confirmation that fMRI responses in auditory cortex do not behave in a linear manner, temporal patterns of imaging noise were found to modulate both the shape and spatial extent of hemodynamic responses, with classically non-auditory areas exhibiting responses to longer duration noise conditions. Hemispheric analysis revealed the right primary auditory cortex to be more sensitive than the left to the presence of imaging related acoustic noise. Right primary auditory cortex responses were significantly larger during all the conditions. This asymmetry of response to imaging related acoustic noise could lead to different baseline activation levels during acquisition schemes using short TR, inducing an observed asymmetry in the responses to an intended acoustic stimulus through limitations of dynamic range, rather than due to differences in neuronal processing of the stimulus. These results emphasize the importance of accounting for the temporal pattern of the acoustic noise when comparing findings across different fMRI studies, especially those involving acoustic stimulation. PMID:26519093

  7. Flight Acoustic Testing and Data Acquisition For the Rotor Noise Model (RNM)

    NASA Technical Reports Server (NTRS)

    Conner, David A.; Burley, Casey L.; Smith, Charles D.

    2006-01-01

    Two acoustic flight tests have been conducted on a remote test range at Eglin Air Force Base in the panhandle of Florida. The first was the Acoustics Week flight test conducted in September 2003. The second was the NASA Heavy Lift Rotorcraft Acoustics Flight Test conducted in October-November 2005. Benchmark acoustic databases were obtained for a number of rotorcraft and limited fixed wing vehicles for a variety of flight conditions. The databases are important for validation of acoustic prediction programs such as the Rotorcraft Noise Model (RNM), as well as for the development of low noise flight procedures and for environmental impact assessments. An overview of RNM capabilities and a detailed description of the RNM/ART (Acoustic Repropagation Technique) process are presented. The RNM/ART process is demonstrated using measured acoustic data for the MD600N. The RNM predictions for a level flyover speed sweep show the highest SEL noise levels on the flight track centerline occurred at the slowest vehicle speeds. At these slower speeds, broadband noise content is elevated compared to noise levels obtained at the higher speeds. A descent angle sweep shows that, in general, ground noise levels increased with increasing descent rates. Vehicle orientation in addition to vehicle position was found to significantly affect the RNM/ART creation of source noise semi-spheres for vehicles with highly directional noise characteristics and only mildly affect those with weak acoustic directionality. Based on these findings, modifications are proposed for RNM/ART to more accurately define vehicle and rotor orientation.

  8. Flight Acoustic Testing and For the Rotorcraft Noise Data Acquisition Model (RNM)

    NASA Technical Reports Server (NTRS)

    Burley, Casey L.; Smith, Charles D.; Conner, David A.

    2006-01-01

    Two acoustic flight tests have been conducted on a remote test range at Eglin Air Force Base in the panhandle of Florida. The first was the "Acoustics Week" flight test conducted in September 2003. The second was the NASA Heavy Lift Rotorcraft Acoustics Flight Test conducted in October-November 2005. Benchmark acoustic databases were obtained for a number of rotorcraft and limited fixed wing vehicles for a variety of flight conditions. The databases are important for validation of acoustic prediction programs such as the Rotorcraft Noise Model (RNM), as well as for the development of low noise flight procedures and for environmental impact assessments. An overview of RNM capabilities and a detailed description of the RNM/ART (Acoustic Repropagation Technique) process are presented. The RNM/ART process is demonstrated using measured acoustic data for the MD600N. The RNM predictions for a level flyover speed sweep show the highest SEL noise levels on the flight track centerline occurred at the slowest vehicle speeds. At these slower speeds, broadband noise content is elevated compared to noise levels obtained at the higher speeds. A descent angle sweep shows that, in general, ground noise levels increased with increasing descent rates. Vehicle orientation in addition to vehicle position was found to significantly affect the RNM/ART creation of source noise semi-spheres for vehicles with highly directional noise characteristics and only mildly affect those with weak acoustic directionality. Based on these findings, modifications are proposed for RNM/ART to more accurately define vehicle and rotor orientation.

  9. Modeling Hemodynamic Responses in Auditory Cortex at 1.5T Using Variable Duration Imaging Acoustic Noise

    PubMed Central

    Hu, Shuowen; Olulade, Olumide; Gonzalez, Javier Castillo; Santos, Joseph; Kim, Sungeun; Tamer, Gregory G.; Luh, Wen-Ming; Talavage, Thomas M.

    2009-01-01

    A confound for functional magnetic resonance imaging (fMRI), especially for auditory studies, is the presence of imaging acoustic noise generated mainly as a byproduct of rapid gradient switching during volume acquisition and to a lesser extent, the radio-frequency transmit. This work utilized a novel pulse sequence to present actual imaging acoustic noise for characterization of the induced hemodynamic responses and assessment of linearity in the primary auditory cortex with respect to noise duration. Results show that responses to brief duration (46ms) imaging acoustic noise is highly nonlinear while responses to longer duration (>1s) imaging acoustic noise becomes approximately linear, with the right primary auditory cortex exhibiting a higher degree of nonlinearity than the left for the investigated noise durations. This study also assessed the spatial extent of activation induced by imaging acoustic noise, showing that the use of modeled responses (specific to imaging acoustic noise) as the reference waveform revealed additional activations in the auditory cortex not observed with a canonical gamma variate reference waveform, suggesting an improvement in detection sensitivity for imaging acoustic noise-induced activity. Longer duration (1.5s) imaging acoustic noise was observed to induce activity that expanded outwards from Heschl’s gyrus to cover the superior temporal gyrus as well as parts of the middle temporal gyrus and insula, potentially affecting higher level acoustic processing. PMID:19948232

  10. Acoustic confort at home: Noise emitted by house installations. Recommendations in order to avoid such noise

    NASA Astrophysics Data System (ADS)

    Jimenez, Santiago

    2002-11-01

    The present survey consists of the analysis and the study of the solutions used at present in the installations of water supply and elevators. It has been carried out from the acoustic point of view. In order to achieve a thorough study a pilot plant was built in the Laboratory of Acoustics of the School of Industrial Engineering of Terrassa. This pilot plant reproduced different kinds of installations of the water supply in houses. And it has allowed us to systematize the measures and also to determine the optimum solutions from the acoustic perspective. In accordance with the objectives and the process of the survey, the solutions regularly employed in the facilities of water supply and elevators in houses have been analyzed, and levels of noise associated to these facilities have been also presented. A summary of the results obtained in the plant has been included, according to diverse variables. Both the conclusions of the analysis of the data obtained in the laboratory and those of the installations of the houses have been also compared, which has allowed us to describe a series of suggestions with the purpose of reducing the acoustic emission of this type of installations, and increase the acoustic comfort at home. (To be presented in Spanish.)

  11. An objective method and measuring equipment for noise control and acoustic diagnostics of motorcars. [acoustic diagnostics on automobile engines

    NASA Technical Reports Server (NTRS)

    Kacprowski, J.; Motylewski, J.; Miazga, J.

    1974-01-01

    An objective method and apparatus for noise control and acoustic diagnostics of motorcar engines are reported. The method and apparatus let us know whether the noisiness of the vehicle under test exceeds the admissible threshold levels given by appropriate standards and if so what is the main source of the excessive noise. The method consists in measuring both the overall noise level and the sound pressure levels in definite frequency bands while the engine speed is controlled as well and may be fixed at prescribed values. Whenever the individually adjusted threshold level has been exceeded in any frequency band, a self-sustaining control signal is sent.

  12. Non-linear generation of acoustic noise in the IAR spacecraft

    NASA Technical Reports Server (NTRS)

    Westley, R.; Nguyen, K.; Westley, M. S.

    1990-01-01

    The requirement to produce high level acoustic noise fields with increasing accuracy in environmental test facilities dictates that a more precise understanding is required of the factors controlling nonlinear noise generation. Details are given of various nonlinear effects found in acoustic performance data taken from the IAR Spacecraft Acoustic Chamber. This type of data has enabled the IAR to test large spacecraft to relatively tight acoustic tolerances over a wide frequency range using manually set controls. An analog random noise automatic control system was available and modified to provide automatic selection of the chamber's spectral sound pressure levels. The automatic control system when used to complete a typical qualification test appeared to equal the accuracy of the manual system and had the added advantage that parallel spectra could be easily achieved during preset tests.

  13. Determination of acoustic attenuation in the Hudson River Estuary by means of ship noise observations.

    PubMed

    Roh, Heui-Seol; Sutin, Alexander; Bunin, Barry

    2008-06-01

    Analysis of sound propagation in a complex urban estuary has application to underwater threat detection systems, underwater communication, and acoustic tomography. One of the most important acoustic parameters, sound attenuation, was analyzed in the Hudson River near Manhattan using measurements of acoustic noise generated by passing ships and recorded by a fixed hydrophone. Analysis of the ship noise level for varying distances allowed estimation of the sound attenuation in the frequency band of 10-80 kHz. The effective attenuation coefficient representing the attenuation loss above cylindrical spreading loss had only slight frequency dependence and can be estimated by the frequency independent value of 0.058 dBm.

  14. High level white noise generator

    DOEpatents

    Borkowski, Casimer J.; Blalock, Theron V.

    1979-01-01

    A wide band, stable, random noise source with a high and well-defined output power spectral density is provided which may be used for accurate calibration of Johnson Noise Power Thermometers (JNPT) and other applications requiring a stable, wide band, well-defined noise power spectral density. The noise source is based on the fact that the open-circuit thermal noise voltage of a feedback resistor, connecting the output to the input of a special inverting amplifier, is available at the amplifier output from an equivalent low output impedance caused by the feedback mechanism. The noise power spectral density level at the noise source output is equivalent to the density of the open-circuit thermal noise or a 100 ohm resistor at a temperature of approximately 64,000 Kelvins. The noise source has an output power spectral density that is flat to within 0.1% (0.0043 db) in the frequency range of from 1 KHz to 100 KHz which brackets typical passbands of the signal-processing channels of JNPT's. Two embodiments, one of higher accuracy that is suitable for use as a standards instrument and another that is particularly adapted for ambient temperature operation, are illustrated in this application.

  15. Computer-controlled noise adaption for acoustical test facilities

    NASA Astrophysics Data System (ADS)

    Wedig, W. V.; Ams, A.

    1990-09-01

    For acoustical noise tests of elastic structures, statistically representative signals generated from white noise by means of spectrum shapers and band pass filters are needed. Subsequently, these signals are amplified and transformed into physical test noise by acoustical sirens. A mathematical model of the entire system based on measurements of frequency transfer functions in order to predict an optimal amplitude modulation of the spectrum shaper is presented. The prediction is performed by means of a nonlinear optimization procedure which iterates the tuning parameters of the shaper with respect to the stored frequency data of the entire system.

  16. Quantitative Measures of Anthropogenic Noise on Harbor Porpoises: Testing the Reliability of Acoustic Tag Recordings.

    PubMed

    Wisniewska, Danuta M; Teilmann, Jonas; Hermannsen, Line; Johnson, Mark; Miller, Lee A; Siebert, Ursula; Madsen, Peter Teglberg

    2016-01-01

    In recent years, several sound and movement recording tags have been developed to sample the acoustic field experienced by cetaceans and their reactions to it. However, little is known about how tag placement and an animal's orientation in the sound field affect the reliability of on-animal recordings as proxies for actual exposure. Here, we quantify sound exposure levels recorded with a DTAG-3 tag on a captive harbor porpoise exposed to vessel noise in a controlled acoustic environment. Results show that flow noise is limiting onboard noise recordings, whereas no evidence of body shading has been found for frequencies of 2-20 kHz.

  17. Model helicopter rotor high-speed impulsive noise: Measured acoustics and blade pressures

    NASA Technical Reports Server (NTRS)

    Boxwell, D. A.; Schmitz, F. H.; Splettstoesser, W. R.; Schultz, K. J.

    1983-01-01

    A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels are known to be dominant. Model-rotor measurements of the peak acoustic pressure levels, waveform shapes, and directively patterns are directly compared with full-scale investigations, using an equivalent in-flight technique. Model acoustic data are shown to scale remarkably well in shape and in amplitude with full-scale results. Model rotor-blade pressures are presented for rotor operating conditions both with and without shock-like discontinuities in the radiated acoustic waveform. Acoustically, both model and full-scale measurements support current evidence that above certain high subsonic advancing-tip Mach numbers, local shock waves that exist on the rotor blades ""delocalize'' and radiate to the acoustic far-field.

  18. Publications in acoustic and noise control from NASA Langley Research Center during 1940-1979. [bibliographies

    NASA Technical Reports Server (NTRS)

    Fryer, B. A. (Compiler)

    1980-01-01

    Reference lists of approximately 900 published Langley Research Center reports in various areas of acoustics and noise control for the period 1940-1979 are presented. Specific topic areas covered include: duct acoustics; propagation and operations; rotating blade noise; jet noise; sonic boom; flow surface interaction noise; structural response/interior noise; human response; and noise prediction.

  19. Computational AeroAcoustics for Fan Noise Prediction

    NASA Technical Reports Server (NTRS)

    Envia, Ed; Hixon, Ray; Dyson, Rodger; Huff, Dennis (Technical Monitor)

    2002-01-01

    An overview of the current state-of-the-art in computational aeroacoustics as applied to fan noise prediction at NASA Glenn is presented. Results from recent modeling efforts using three dimensional inviscid formulations in both frequency and time domains are summarized. In particular, the application of a frequency domain method, called LINFLUX, to the computation of rotor-stator interaction tone noise is reviewed and the influence of the background inviscid flow on the acoustic results is analyzed. It has been shown that the noise levels are very sensitive to the gradients of the mean flow near the surface and that the correct computation of these gradients for highly loaded airfoils is especially problematic using an inviscid formulation. The ongoing development of a finite difference time marching code that is based on a sixth order compact scheme is also reviewed. Preliminary results from the nonlinear computation of a gust-airfoil interaction model problem demonstrate the fidelity and accuracy of this approach. Spatial and temporal features of the code as well as its multi-block nature are discussed. Finally, latest results from an ongoing effort in the area of arbitrarily high order methods are reviewed and technical challenges associated with implementing correct high order boundary conditions are discussed and possible strategies for addressing these challenges ore outlined.

  20. High Frequency Acoustic Channel Characterization for Propagation and Ambient Noise

    DTIC Science & Technology

    2007-09-30

    close collaboration with Michael Porter and Paul Hursky (HLS Research) with support from the ONR Ocean Acoustics Program and the ONR PLUSNet Project...Siderius, Chris Harrison and Michael Porter , “A passive fathometer for determining bottom depth and imaging seabed layering using ambient noise”, J...noise processing for estimation of seabed layering”, J. Acoust. Soc. Am., (2007) [submitted, refereed]. [8] Martin Siderius and Michael Porter , “Modeling

  1. Acoustic Noise Induces Attention Shifts and Reduces Foraging Performance in Three-Spined Sticklebacks (Gasterosteus aculeatus)

    PubMed Central

    Purser, Julia; Radford, Andrew N.

    2011-01-01

    Acoustic noise is known to have a variety of detrimental effects on many animals, including humans, but surprisingly little is known about its impacts on foraging behaviour, despite the obvious potential consequences for survival and reproductive success. We therefore exposed captive three-spined sticklebacks (Gasterosteus aculeatus) to brief and prolonged noise to investigate how foraging performance is affected by the addition of acoustic noise to an otherwise quiet environment. The addition of noise induced only mild fear-related behaviours - there was an increase in startle responses, but no change in the time spent freezing or hiding compared to a silent control - and thus had no significant impact on the total amount of food eaten. However, there was strong evidence that the addition of noise increased food-handling errors and reduced discrimination between food and non-food items, results that are consistent with a shift in attention. Consequently, noise resulted in decreased foraging efficiency, with more attacks needed to consume the same number of prey items. Our results suggest that acoustic noise has the potential to influence a whole host of everyday activities through effects on attention, and that even very brief noise exposure can cause functionally significant impacts, emphasising the threat posed by ever-increasing levels of anthropogenic noise in the environment. PMID:21386909

  2. Noise levels of operational helicopters of the OH-6 type designed to meet the LOH mission. [acoustic properties for various helicopter configurations

    NASA Technical Reports Server (NTRS)

    Wagner, R. A.

    1973-01-01

    Formulas relating overall sound pressure level (OASPL) to parameters such as horsepower required, tip speed, and thrust for main and tail rotors are presented for standard and quieted helicopters. Formulas relating OASPL to engine parameters such as horsepower output and percent power turbine rpm are presented for unmuffled and muffled engines. The linear scale was used in preference to any of the weighted scales because it resulted in more consistent agreement with the test data when the SPL is expressed in the usual parameters of tip speed, thrust generated and power required. It is recognized that the linear scale does not adequately reflect hearing response, and hence is not a good absolute measure for detection by humans. However, linear OASPL is believed to be useful as a relative means of comparing noise level variations of individual components in similar helicopters with reasonably modest design changes.

  3. Single stage, low noise advanced technology fan. Volume 3: Acoustic design

    NASA Technical Reports Server (NTRS)

    Kazin, S. B.; Mishler, R. B.

    1976-01-01

    The acoustic design for a half-scale fan vehicle, which would have application on an advanced transport aircraft, is described. The single stage advanced technology fan was designed to a pressure ratio of 1.8 at a tip speed of 503 m/sec (1,650 ft/sec). The two basic approaches taken in the acoustic design were: (1) minimization of noise at the source, and (2) suppression of the generated noise in the inlet and bypass exhaust duct. Suppression of the generated noise is accomplished in the inlet through use of the hybrid concept (wall acoustic treatment plus airflow acceleration suppression) and in the exhaust duct with extensive acoustic treatment including a splitter. The goal of the design was attainment of twenty effective perceived noise decibels (20 EPNdB) below current Federal Air Regulation noise standards for a full-scale fan at the takeoff, cutback, and approach conditions. Predicted unsuppressed and suppressed fore and aft maximum perceived noise levels indicate that the cutback condition is the most critical with respect to the goal, which is probably unattainable for that condition. This is also true for aft radiated noise in the approach condition.

  4. Noise Hazard Evaluation Sound Level Data on Noise Sources

    DTIC Science & Technology

    1975-01-01

    AD-A021 465 NOISE HAZARD EfALUATION SOUND LEVEL DATA ON NOISE SOURCES Jeffrey Goldstein Army Environmental Hygiene Agency Prepared for: Army Health ...A. Noise Hazard Evaluation. B. Engineering Noise Control. C. Health Education. D. Audiometry. E. Hearing Protection. This technical guide concerns the...SOUND LEVEL DATA OF NOISE SOURCES Approved for public release, distribution unlimited. jGI4A C4C SENTINEL HEALTH I 5 US ARMY ENVIROIN.MENTAL HYGIENE

  5. Acoustics, Noise, and Buildings. Revised Edition 1969.

    ERIC Educational Resources Information Center

    Parkin, P. H.; Humphreys, H. R.

    The fundamental physical concepts needed in any appreciation of acoustical problems are discussed by a scientist and an architect. The major areas of interest are--(1) the nature of sound, (2) the behavior of sound in rooms, (3) the design of rooms for speech, (4) the design of rooms for music, (5) the design of studios, (6) the design of high…

  6. Statistical Analysis and Computer Generation of Spatially Correlated Acoustic Noise (Preprint)

    DTIC Science & Technology

    2006-05-01

    this paper, we describe an approach for generating simulated acoustic noise with a spatial correlation coefficient distribution and maximum extreme... correlation coefficient and MEV distributions which drive the computer generation of a large number of simulated acoustic noise signals.

  7. Acoustics

    NASA Technical Reports Server (NTRS)

    Goodman, Jerry R.; Grosveld, Ferdinand

    2007-01-01

    The acoustics environment in space operations is important to maintain at manageable levels so that the crewperson can remain safe, functional, effective, and reasonably comfortable. High acoustic levels can produce temporary or permanent hearing loss, or cause other physiological symptoms such as auditory pain, headaches, discomfort, strain in the vocal cords, or fatigue. Noise is defined as undesirable sound. Excessive noise may result in psychological effects such as irritability, inability to concentrate, decrease in productivity, annoyance, errors in judgment, and distraction. A noisy environment can also result in the inability to sleep, or sleep well. Elevated noise levels can affect the ability to communicate, understand what is being said, hear what is going on in the environment, degrade crew performance and operations, and create habitability concerns. Superfluous noise emissions can also create the inability to hear alarms or other important auditory cues such as an equipment malfunctioning. Recent space flight experience, evaluations of the requirements in crew habitable areas, and lessons learned (Goodman 2003; Allen and Goodman 2003; Pilkinton 2003; Grosveld et al. 2003) show the importance of maintaining an acceptable acoustics environment. This is best accomplished by having a high-quality set of limits/requirements early in the program, the "designing in" of acoustics in the development of hardware and systems, and by monitoring, testing and verifying the levels to ensure that they are acceptable.

  8. Perceptual Learning of Acoustic Noise by Individuals with Dyslexia

    ERIC Educational Resources Information Center

    Agus, Trevor R.; Carrión-Castillo, Amaia; Pressnitzer, Daniel; Ramus, Franck

    2014-01-01

    Purpose: A phonological deficit is thought to affect most individuals with developmental dyslexia. The present study addresses whether the phonological deficit is caused by difficulties with perceptual learning of fine acoustic details. Method: A demanding test of nonverbal auditory memory, "noise learning," was administered to both…

  9. Perceptual learning of acoustic noise generates memory-evoked potentials.

    PubMed

    Andrillon, Thomas; Kouider, Sid; Agus, Trevor; Pressnitzer, Daniel

    2015-11-02

    Experience continuously imprints on the brain at all stages of life. The traces it leaves behind can produce perceptual learning [1], which drives adaptive behavior to previously encountered stimuli. Recently, it has been shown that even random noise, a type of sound devoid of acoustic structure, can trigger fast and robust perceptual learning after repeated exposure [2]. Here, by combining psychophysics, electroencephalography (EEG), and modeling, we show that the perceptual learning of noise is associated with evoked potentials, without any salient physical discontinuity or obvious acoustic landmark in the sound. Rather, the potentials appeared whenever a memory trace was observed behaviorally. Such memory-evoked potentials were characterized by early latencies and auditory topographies, consistent with a sensory origin. Furthermore, they were generated even on conditions of diverted attention. The EEG waveforms could be modeled as standard evoked responses to auditory events (N1-P2) [3], triggered by idiosyncratic perceptual features acquired through learning. Thus, we argue that the learning of noise is accompanied by the rapid formation of sharp neural selectivity to arbitrary and complex acoustic patterns, within sensory regions. Such a mechanism bridges the gap between the short-term and longer-term plasticity observed in the learning of noise [2, 4-6]. It could also be key to the processing of natural sounds within auditory cortices [7], suggesting that the neural code for sound source identification will be shaped by experience as well as by acoustics.

  10. A comparative evaluation of three types of acoustic noise generators

    NASA Technical Reports Server (NTRS)

    Cook, L. L., Jr.; Johnson, H. B., Jr.

    1974-01-01

    Assessment of the operation and performance characteristics of three acoustic noise generators (a siren, an electropneumatic modulator, and an electrohydraulic modulator) when used in conjunction with a progressive wave tube. Particularly, the spectrum shaping capabilities and efficiencies of the three generators are compared.

  11. Development of an acoustic actuator for launch vehicle noise reduction.

    PubMed

    Henderson, Benjamin K; Lane, Steven A; Gussy, Joel; Griffin, Steve; Farinholt, Kevin M

    2002-01-01

    In many active noise control applications, it is necessary that acoustic actuators be mounted in small enclosures due to volume constraints and in order to remain unobtrusive. However, the air spring of the enclosure is detrimental to the low-frequency performance of the actuator. For launch vehicle noise control applications, mass and volume constraints are very limiting, but the low-frequency performance of the actuator is critical. This work presents a novel approach that uses a nonlinear buckling suspension system and partial evacuation of the air within the enclosure to yield a compact, sealed acoustic driver that exhibits a very low natural frequency. Linear models of the device are presented and numerical simulations are given to illustrate the advantages of this design concept. An experimental prototype was built and measurements indicate that this design can significantly improve the low-frequency response of compact acoustic actuators.

  12. HOW TO KEEP SCHOOL NOISE AT THE RIGHT LEVEL.

    ERIC Educational Resources Information Center

    MCKAY, RONALD L.

    DISCUSSES FACTORS TO BE CONSIDERED DURING SCHOOL PLANNING STAGES REGARDING NOISE LEVELS AND ACOUSTIC DESIGN IMPLICATIONS. FACTORS ARE--(1) A STAGE HOUSE IS DETRIMENTAL TO ORCHESTRAS, BANDS, CHORUSES, LECTURES, ASSEMBLIES, RECITALS, AND CERTAIN DRAMAS AND SPEECH-MUSIC PERFORMANCES. SUGGESTED IS AN AUDITORIUM WITH AUDIENCE AND PERFORMING PLATFORM…

  13. Developing general acoustic model for noise sources and parameters estimation

    NASA Astrophysics Data System (ADS)

    Madoliat, Reza; Nouri, Nowrouz Mohammad; Rahrovi, Ali

    2017-02-01

    Noise measured at various points around the environment can be evaluated by a series of acoustic sources. Acoustic sources with wide surface can be broken down in fluid environment using some smaller acoustic sources. The aim of this study is to make a model to indicate the type, number, direction, position and strength of these sources in a way that the main sound and the sound of equivalent sources match together in an acceptable way. When position and direction of the source is given, the strength of the source can be found using inverse method. On the other hand, considering the non-uniqueness of solution in inverse method, a different acoustic strength is obtained for the sources if different positions are selected. Selecting an arrangement of general source and using the optimization algorithm, the least possible mismatch between the main sound and the sound of equivalent sources can be achieved.

  14. Acoustic Environment of Admiralty Inlet: Broadband Noise Measurements

    SciTech Connect

    Xu, Jinshan; Deng, Zhiqun; Martinez, Jayson J.; Carlson, Thomas J.; Myers, Joshua R.; Weiland, Mark A.; Jones, Mark E.

    2011-09-30

    Admiralty Inlet has been selected as a potential tidal energy site. It is located near shipping lanes, is a highly variable acoustic environment, and is frequented by the highly endangered southern resident killer whale (SRKW). Resolving environmental impacts is the first step to receiving approval to deploy tidal turbines at Admiralty Inlet. Of particular concern is the potential for blade strike or other negative interactions between the SRKW and the tidal turbine. A variety of technologies including passive and active monitoring systems are being considered as potential tools to determine the presence of SRKW in the vicinity of the turbines. Broadband noise level measurements are critical for the determination of design and operation specifications of all marine and hydrokinetic energy capture technologies. Acoustic environment data at the proposed site was acquired at different depths using a cabled vertical line array (VLA) with four calibrated hydrophones. The sound pressure level (SPL) power spectrum density was estimated based on the fast Fourier transform. This study describes the first broadband SPL measurements for this site at different depths with frequency ranging from 10 kHz to 480 kHz in combination with other information. To understand the SPL caused by this bedload transport, three different pressure sensors with temperature and conductivity were also assembled on the VLA to measure the conditions at the hydrophone deployment depth. The broadband SPL levels at frequency ranges of 3 kHz to 7 kHz as a function of depth were estimated. Only the hydrophone at an average depth of 40 m showed the strong dependence of SPL with distance from the bottom, which was possibly caused by the cobbles shifting on the seabed. Automatic Identification System data were also studied to understand the SPL measurements.

  15. Airframe noise measurements by acoustic imaging

    NASA Technical Reports Server (NTRS)

    Kendall, J. M.

    1977-01-01

    Studies of the noise produced by flow past wind tunnel models are presented. The central objective of these is to find the specific locations within a flow which are noisy, and to identify the fluid dynamic processes responsible, with the expectation that noise reduction principles will be discovered. The models tested are mostly simple shapes which result in types of flow that are similar to those occurring on, for example, aircraft landing gear and wheel cavities. A model landing gear and a flap were also tested. Turbulence has been intentionally induced as appropriate in order to simulate full-scale effects more closely. The principal technique involves use of a highly directional microphone system which is scanned about the flow field to be analyzed. The data so acquired are presented as a pictorial image of the noise source distribution. An important finding is that the noise production is highly variable within a flow field and that sources can be attributed to various fluid dynamic features of the flow. Flow separation was not noisy, but separation closure usually was.

  16. Near-field acoustical holography of military jet aircraft noise

    NASA Astrophysics Data System (ADS)

    Wall, Alan T.; Gee, Kent L.; Neilsen, Tracianne; Krueger, David W.; Sommerfeldt, Scott D.; James, Michael M.

    2010-10-01

    Noise radiated from high-performance military jet aircraft poses a hearing-loss risk to personnel. Accurate characterization of jet noise can assist in noise prediction and noise reduction techniques. In this work, sound pressure measurements were made in the near field of an F-22 Raptor. With more than 6000 measurement points, this is the most extensive near-field measurement of a high-performance jet to date. A technique called near-field acoustical holography has been used to propagate the complex pressure from a two- dimensional plane to a three-dimensional region in the jet vicinity. Results will be shown and what they reveal about jet noise characteristics will be discussed.

  17. Trailing Edge Noise Prediction Based on a New Acoustic Formulation

    NASA Technical Reports Server (NTRS)

    Casper, J.; Farassat, F.

    2002-01-01

    A new analytic result in acoustics called 'Formulation 1B,' proposed by Farassat, is used to compute broadband trailing edge noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term, and has been shown in previous research to provide time domain predictions of broadband noise that are in excellent agreement with experiment. Furthermore, this formulation lends itself readily to rotating reference frames and statistical analysis of broadband trailing edge noise. Formulation 1B is used to calculate the far field noise radiated from the trailing edge of a NACA 0012 airfoil in low Mach number flows, using both analytical and experimental data on the airfoil surface. The results are compared to analytical results and experimental measurements that are available in the literature. Good agreement between predictions and measurements is obtained.

  18. Combined effect of noise and room acoustics on vocal effort in simulated classrooms.

    PubMed

    Cipriano, Marcella; Astolfi, Arianna; Pelegrín-García, David

    2017-01-01

    This work investigated the relationships between room acoustics, background noise level, and vocal effort of a speaker in simulated classrooms of various volumes. Under simulated acoustic environments, talkers adjusted their vocal effort linearly with the voice support, i.e., the degree of amplification offered by the room to the voice of a speaker, at his own ears. The slope of this relationship, called the room effect, of -0.24 dB/dB was significant only in the case of the highest noise levels of 62 dB. The vocal comfort for the speaker, however, was found to be more closely related to noise annoyance than to room reverberance.

  19. Computer program to predict aircraft noise levels

    NASA Technical Reports Server (NTRS)

    Clark, B. J.

    1981-01-01

    Methods developed at the NASA Lewis Research Center for predicting the noise contributions from various aircraft noise sources were programmed to predict aircraft noise levels either in flight or in ground tests. The noise sources include fan inlet and exhaust, jet, flap (for powered lift), core (combustor), turbine, and airframe. Noise propagation corrections are available for atmospheric attenuation, ground reflections, extra ground attenuation, and shielding. Outputs can include spectra, overall sound pressure level, perceived noise level, tone-weighted perceived noise level, and effective perceived noise level at locations specified by the user. Footprint contour coordinates and approximate footprint areas can also be calculated. Inputs and outputs can be in either System International or U.S. customary units. The subroutines for each noise source and propagation correction are described. A complete listing is given.

  20. Noise transmission through an acoustically treated and honeycomb stiffened aircraft sidewall

    NASA Astrophysics Data System (ADS)

    Grosveld, F. W.; Mixson, J. S.

    1984-10-01

    The noise transmission characteristics of test panels and acoustic treatments representative of an aircraft sidewall are experimentally investigated in the NASA Langley Research Center transmission loss apparatus. The test panels were built to represent a segment sidewall in the propeller plane of a twin-engine, turboprop light aircraft. It is shown that an advanced treatment, which uses honeycomb for structural stiffening of skin panels, has better noise transmission loss characteristics than a conventional treatment. An alternative treatment, using the concept of limp mass and vibration isolation, provides more transmission loss than the advanced treatment for the same total surface mass. Effects on transmission loss of a variety of acoustic treatment materials (acoustic blankets, septa, damping tape, and trim panels) are presented. Damping tape does not provide additional benefit when the other treatment provides a high level of damping. Window units representative of aircraft installations are shown to have low transmission loss relative to a completely treated sidewall.

  1. Propagation and Ambient Noise Studies for Ocean Acoustics Applications

    DTIC Science & Technology

    2010-09-30

    using the OASN tool based on the OASES propagation codes [6] with details of the results in publication [3] and summarized in the next sections...reason for this poor performance was investigated through simulation by applying the BF algorithms to CSD matrices produced by OASN (from the OASES ...ambient noise sub- bottom profiling”, J. Acoust. Soc. Am., 118 (5), 2913–2923, 2005. 6. H. Schmidt, “ OASES user’s guide and reference manual”, MIT

  2. Assessment Of Acoustic Adaptations For Noise Compensation In Marine Mammals

    DTIC Science & Technology

    2009-09-30

    sounds on the use of sound by marine mammals. OBJECTIVES The primary objectives of this project are to: 1) generate testable hypotheses of...general vocal responses of marine mammals to particular noise types; and 2) test these hypotheses with data from two low-frequency baleen whale species...in coastal shallow water environments using existing data from North Atlantic right whale (Eubalaena glacialis) acoustic tag recordings (Digital

  3. Assessment of Acoustic Adaptations for Noise Compensation in Marine Mammals

    DTIC Science & Technology

    2012-09-30

    made sounds on the use of sound by marine mammals. OBJECTIVES The primary objectives of this project are to: 1) generate testable hypotheses...of general vocal responses of marine mammals to particular noise types; and 2) test these hypotheses with data from two low-frequency baleen whale ...species in coastal shallow water environments using existing data from North Atlantic right whale (Eubalaena glacialis) acoustic tag recordings

  4. Assessment of Acoustic Adaptations for Noise Compensation in Marine Mammals

    DTIC Science & Technology

    2011-09-30

    made sounds on the use of sound by marine mammals. OBJECTIVES The primary objectives of this project are to: 1) generate testable hypotheses...of general vocal responses of marine mammals to particular noise types; and 2) test these hypotheses with data from two low-frequency baleen whale ...species in coastal shallow water environments using existing data from North Atlantic right whale (Eubalaena glacialis) acoustic tag recordings

  5. Prediction of jet mixing noise with Lighthill's Acoustic Analogy and geometrical acoustics.

    PubMed

    Ilário, Carlos R S; Azarpeyvand, Mahdi; Rosa, Victor; Self, Rod H; Meneghini, Júlio R

    2017-02-01

    A computational aeroacoustics prediction tool based on the application of Lighthill's theory is presented to compute noise from subsonic turbulent jets. The sources of sound are modeled by expressing Lighthill's source term as two-point correlations of the velocity fluctuations and the sound refraction effects are taken into account by a ray tracing methodology. Both the source and refraction models use the flow information collected from a solution of the Reynolds Averaged Navier-Stokes equations with a standard k-epsilon turbulence model. By adopting the ray tracing method to compute the refraction effects a high-frequency approximation is implied, while no assumption about the mean flow is needed, enabling the application of the method to jet noise problems with inherently three-dimensional propagation effects. Predictions show good agreement with narrowband measurements for the overall sound pressure levels and spectrum shape in polar angles between 60° and 110° for isothermal and hot jets with acoustic Mach number ranging from 0.5 to 1.0. The method presented herein can be applied as a relatively low cost and robust engineering tool for industrial optimization purposes.

  6. Noise correction of turbulent spectra obtained from Acoustic Doppler Velocimeters

    SciTech Connect

    Durgesh, Vibhav; Thomson, Jim; Richmond, Marshall C.; Polagye, Brian

    2014-03-02

    Accurately estimated auto-spectral density functions are essential for characterization of turbulent flows, and they also have applications in computational fluid dynamics modeling, site and inflow characterization for hydrokinetic turbines, and inflow turbulence generation. The Acoustic Doppler Velocimeter (ADV) provides single-point temporally resolved data, that are used to characterize turbulent flows in rivers, seas, and oceans. However, ADV data are susceptible to contamination from various sources, including instrument noise, which is the intrinsic limit to the accuracy of acoustic velocity measurements. Due to the presence of instrument noise, the spectra obtained are altered at high frequencies. The focus of this study is to develop a robust and effective method for accurately estimating auto-spectral density functions from ADV data by reducing or removing the spectral contribution derived from instrument noise. For this purpose, the “Noise Auto-Correlation” (NAC) approach was developed, which exploits the correlation properties of instrument noise to identify and remove its contribution from spectra. The spectra estimated using the NAC approach exhibit increased fidelity and a slope of -5/3 in the inertial range, which is typically observed for turbulent flows. Finally, this study also compares the effectiveness of low-pass Gaussian filters in removing instrument noise with that of the NAC approach. For the data used in this study, both the NAC and Gaussian filter approaches are observed to be capable of removing instrument noise at higher frequencies from the spectra. However, the NAC results are closer to the expected frequency power of -5/3 in the inertial sub-range.

  7. Topography and biological noise determine acoustic detectability on coral reefs

    NASA Astrophysics Data System (ADS)

    Cagua, E. F.; Berumen, M. L.; Tyler, E. H. M.

    2013-12-01

    Acoustic telemetry is an increasingly common tool for studying the movement patterns, behavior and site fidelity of marine organisms, but to accurately interpret acoustic data, the variability, periodicity and range of detectability between acoustic tags and receivers must be understood. The relative and interactive effects of topography with biological and environmental noise have not been quantified on coral reefs. We conduct two long-term range tests (1- and 4-month duration) on two different reef types in the central Red Sea to determine the relative effect of distance, depth, topography, time of day, wind, lunar phase, sea surface temperature and thermocline on detection probability. Detectability, as expected, declines with increasing distance between tags and receivers, and we find average detection ranges of 530 and 120 m, using V16 and V13 tags, respectively, but the topography of the reef can significantly modify this relationship, reducing the range by ~70 %, even when tags and receivers are in line-of-sight. Analyses that assume a relationship between distance and detections must therefore be used with care. Nighttime detection range was consistently reduced in both locations, and detections varied by lunar phase in the 4-month test, suggesting a strong influence of biological noise (reducing detection probability up to 30 %), notably more influential than other environmental noises, including wind-driven noise, which is normally considered important in open-water environments. Analysis of detections should be corrected in consideration of the diel patterns we find, and range tests or sentinel tags should be used for more than 1 month to quantify potential changes due to lunar phase. Some studies assume that the most usual factor limiting detection range is weather-related noise; this cannot be extrapolated to coral reefs.

  8. A study of interior noise levels, noise sources and transmission paths in light aircraft

    NASA Technical Reports Server (NTRS)

    Hayden, R. E.; Murray, B. S.; Theobald, M. A.

    1983-01-01

    The interior noise levels and spectral characteristics of 18 single-and twin-engine propeller-driven light aircraft, and source-path diagnosis of a single-engine aircraft which was considered representative of a large part of the fleet were studied. The purpose of the flight surveys was to measure internal noise levels and identify principal noise sources and paths under a carefully controlled and standardized set of flight procedures. The diagnostic tests consisted of flights and ground tests in which various parts of the aircraft, such as engine mounts, the engine compartment, exhaust pipe, individual panels, and the wing strut were instrumented to determine source levels and transmission path strengths using the transfer function technique. Predominant source and path combinations are identified. Experimental techniques are described. Data, transfer function calculations to derive source-path contributions to the cabin acoustic environment, and implications of the findings for noise control design are analyzed.

  9. Effects of noise and acoustics in schools on vocal health in teachers.

    PubMed

    Cutiva, Lady Catherine Cantor; Burdorf, Alex

    2015-01-01

    Previous studies on the influence of noise and acoustics in the classroom on voice symptoms among teachers have exclusively relied on self-reports. Since self-reported physical conditions may be biased, it is important to determine the role of objective measurements of noise and acoustics in the presence of voice symptoms. To assess the association between objectively measured and self-reported physical conditions at school with the presence of voice symptoms among teachers. In 12 public schools in Bogotα, we conducted a cross-sectional study among 682 Colombian school workers at 377 workplaces. After signed the informed consent, participants filled out a questionnaire on individual and work-related conditions and the nature and severity of voice symptoms in the past month. Short-term environmental measurements of sound levels, temperature, humidity, and reverberation time were conducted during visits at the workplaces, such as classrooms and offices. Logistic regression analysis was used to determine associations between work-related factors and voice symptoms. High noise levels outside schools (odds ratio [OR] = 1.83; 95% confidence interval [CI]: 1.12-2.99) and self-reported poor acoustics at the workplace (OR = 2.44; 95% CI: 1.88-3.53) were associated with voice symptoms. We found poor agreement between the objective measurements and self-reports of physical conditions at the workplace. This study indicates that noise and acoustics may play a role in the occurrence of voice symptoms among teachers. The poor agreement between objective measurements and self-reports of physical conditions indicate that these are different entities, which argue for inclusion of physical measurements of the working environment in studies on the influence of noise and acoustics on vocal health.

  10. Acoustical Testing Laboratory Developed to Support the Low-Noise Design of Microgravity Space Flight Hardware

    NASA Technical Reports Server (NTRS)

    Cooper, Beth A.

    2001-01-01

    The NASA John H. Glenn Research Center at Lewis Field has designed and constructed an Acoustical Testing Laboratory to support the low-noise design of microgravity space flight hardware. This new laboratory will provide acoustic emissions testing and noise control services for a variety of customers, particularly for microgravity space flight hardware that must meet International Space Station limits on noise emissions. These limits have been imposed by the space station to support hearing conservation, speech communication, and safety goals as well as to prevent noise-induced vibrations that could impact microgravity research data. The Acoustical Testing Laboratory consists of a 23 by 27 by 20 ft (height) convertible hemi/anechoic chamber and separate sound-attenuating test support enclosure. Absorptive 34-in. fiberglass wedges in the test chamber provide an anechoic environment down to 100 Hz. A spring-isolated floor system affords vibration isolation above 3 Hz. These criteria, along with very low design background levels, will enable the acquisition of accurate and repeatable acoustical measurements on test articles, up to a full space station rack in size, that produce very little noise. Removable floor wedges will allow the test chamber to operate in either a hemi/anechoic or anechoic configuration, depending on the size of the test article and the specific test being conducted. The test support enclosure functions as a control room during normal operations but, alternatively, may be used as a noise-control enclosure for test articles that require the operation of noise-generating test support equipment.

  11. Analysis of Vibration and Acoustic Noise in Permanent Magnet Motors.

    NASA Astrophysics Data System (ADS)

    Hwang, Sangmoon

    The drive motor is a frequent source of vibration and acoustic noise in many precision spindle motors. One of the electromagnetic sources of vibration in permanent magnet motors is the torque ripple, consisting of the reluctance torque and electromagnetic torque fluctuation. This type of vibration is becoming more serious with the advent of new high-grade magnets with increased flux density. Acoustic noise of electromagnetic origin is difficult to predict and its exact mechanism is unclear. The mechanism of noise generation should be revealed to design a quieter motor which is the modern customer's demand. For motor operation at low speeds and loads, torque ripple due to the reluctance torque is often a source of vibration and control difficulty. The reluctance torque in a motor was calculated from the flux density by a finite element method and the Maxwell stress method. Effects of design parameters, such as stator slot width, permanent slot width, airgap length and magnetization direction, were investigated. Magnet pole shaping, by gradually decreasing the magnet thickness toward edges, yields a sinusoidal shape of the reluctance torque with reduced harmonics, thus reducing the vibration. This dissertation also presents two motor design techniques: stator tooth notching and rotor pole skewing with magnet pole shaping, and the effect of each method on the output torque. The analysis shows that the reluctance torque can be nearly eliminated by the suggested designs, with minimal sacrifice of the output torque. In permanent magnet DC motors, the most popular design type is the trapezoidal back electro-motive force (BEMF), for switched DC controllers. It is demonstrated that the output torque profile of one phase energized is qualitatively equivalent to the BEMF profile for motors with reduced reluctance torque. It implies that design of BEMF profile is possible by magnetic modeling of a motor, without expensive and time-consuming experiments for different designs

  12. A numerical model for ocean ultra-low frequency noise: wave-generated acoustic-gravity and Rayleigh modes.

    PubMed

    Ardhuin, Fabrice; Lavanant, Thibaut; Obrebski, Mathias; Marié, Louis; Royer, Jean-Yves; d'Eu, Jean-François; Howe, Bruce M; Lukas, Roger; Aucan, Jerome

    2013-10-01

    The generation of ultra-low frequency acoustic noise (0.1 to 1 Hz) by the nonlinear interaction of ocean surface gravity waves is well established. More controversial are the quantitative theories that attempt to predict the recorded noise levels and their variability. Here a single theoretical framework is used to predict the noise level associated with propagating pseudo-Rayleigh modes and evanescent acoustic-gravity modes. The latter are dominant only within 200 m from the sea surface, in shallow or deep water. At depths larger than 500 m, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and the Kerguelen islands reveal: (a) Deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, in which the presence of the ocean bottom amplifies the noise by 10 to 20 dB; (b) in agreement with previous results, the local maxima in the noise spectrum support the theoretical prediction for the vertical structure of acoustic modes; and (c) noise level and variability are well predicted for frequencies up to 0.4 Hz. Above 0.6 Hz, the model results are less accurate, probably due to the poor estimation of the directional properties of wind-waves with frequencies higher than 0.3 Hz.

  13. Structural Acoustic Prediction and Interior Noise Control Technology

    NASA Technical Reports Server (NTRS)

    Mathur, G. P.; Chin, C. L.; Simpson, M. A.; Lee, J. T.; Palumbo, Daniel L. (Technical Monitor)

    2001-01-01

    This report documents the results of Task 14, "Structural Acoustic Prediction and Interior Noise Control Technology". The task was to evaluate the performance of tuned foam elements (termed Smart Foam) both analytically and experimentally. Results taken from a three-dimensional finite element model of an active, tuned foam element are presented. Measurements of sound absorption and sound transmission loss were taken using the model. These results agree well with published data. Experimental performance data were taken in Boeing's Interior Noise Test Facility where 12 smart foam elements were applied to a 757 sidewall. Several configurations were tested. Noise reductions of 5-10 dB were achieved over the 200-800 Hz bandwidth of the controller. Accelerometers mounted on the panel provided a good reference for the controller. Configurations with far-field error microphones outperformed near-field cases.

  14. An investigation of acoustic noise requirements for the Space Station centrifuge facility

    NASA Technical Reports Server (NTRS)

    Castellano, Timothy

    1994-01-01

    Acoustic noise emissions from the Space Station Freedom (SSF) centrifuge facility hardware represent a potential technical and programmatic risk to the project. The SSF program requires that no payload exceed a Noise Criterion 40 (NC-40) noise contour in any octave band between 63 Hz and 8 kHz as measured 2 feet from the equipment item. Past experience with life science experiment hardware indicates that this requirement will be difficult to meet. The crew has found noise levels on Spacelab flights to be unacceptably high. Many past Ames Spacelab life science payloads have required waivers because of excessive noise. The objectives of this study were (1) to develop an understanding of acoustic measurement theory, instruments, and technique, and (2) to characterize the noise emission of analogous Facility components and previously flown flight hardware. Test results from existing hardware were reviewed and analyzed. Measurements of the spectral and intensity characteristics of fans and other rotating machinery were performed. The literature was reviewed and contacts were made with NASA and industry organizations concerned with or performing research on noise control.

  15. Background Noise in Underwater Acoustic Listening Systems

    DTIC Science & Technology

    1979-01-15

    on this subject in a subsequent paper. 20 Lomask and Frassetto, using the bathyscaph TRIESTE, made a series of experiments in the Tyrrhenian Sea where...8217 , I TiON 2o- "APR JUL 0I S10 102 103 10 A I FREQUENCY (H) m I "i-ne ean spctrum evelsartemienaBemuawihheATMSary I SOUTH NORWEGIAN SEA ...MEASUREMENTS 40- 0 101 10 FREQUENCY NHz) Also compared were the mean levels measured in the Southern Norwegian Sea by Walkinshaw and Vidale. This shows

  16. Acoustic Investigation of Jet Mixing Noise in Dual Stream Nozzles

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas; Dahl, Milo D.

    2012-01-01

    In an earlier study, a prediction model for jet noise in dual stream jets was proposed that is founded on velocity scaling laws in single stream jets and similarity features of the mean velocity and turbulent kinetic energy in dual stream flows. The model forms a composite spectrum from four component single-stream jets each believed to represent noise-generation from a distinct region in the actual flow. While the methodology worked effectively at conditions considered earlier, recent examination of acoustic data at some unconventional conditions indicate that further improvements are necessary in order to expand the range of applicability of the model. The present work demonstrates how these predictions compare with experimental data gathered by NASA and industry for the purpose of examining the aerodynamic and acoustic performance of such nozzles for a wide range of core and fan stream conditions. Of particular interest are jets with inverted velocity and temperature profiles and the appearance of a second spectral peak at small aft angles to the jet under such conditions. It is shown that a four-component spectrum succeeds in modeling the second peak when the aft angle refraction effects are properly incorporated into the model. A tradeoff of noise emission takes place between two turbulent regions identified as transition and fully mixed regions as the fan stream velocity exceeds that of the core stream. The effect of nozzle discharge coefficients will also be discussed.

  17. Nonlinear Transport and Noise Properties of Acoustic Phonons

    NASA Astrophysics Data System (ADS)

    Walczak, Kamil

    We examine heat transport carried by acoustic phonons in molecular junctions composed of organic molecules coupled to two thermal baths of different temperatures. The phononic heat flux and its dynamical noise properties are analyzed within the scattering (Landauer) formalism with transmission probability function for acoustic phonons calculated within the method of atomistic Green's functions (AGF technique). The perturbative computational scheme is used to determine nonlinear corrections to phononic heat flux and its noise power spectral density with up to the second order terms with respect to temperature difference. Our results show the limited applicability of ballistic Fourier's law and fluctuation-dissipation theorem to heat transport in quantum systems. We also derive several noise-signal relations applicable to nanoscale heat flow carried by phonons, but valid for electrons as well. We also discuss the extension of the perturbative transport theory to higher order terms in order to address a huge variety of problems related to nonlinear thermal effects which may occur at nanoscale and at strongly non-equilibrium conditions with high-intensity heat fluxes. This work was supported by Pace University Start-up Grant.

  18. Propagation of high frequency jet noise using geometric acoustics

    NASA Technical Reports Server (NTRS)

    Khavaran, A.; Krejsa, E. A.

    1993-01-01

    Spherical directivity of noise radiated from a convecting quadrupole source embedded in an arbitrary spreading jet is obtained by ray-tracing methods of geometrical acoustics. The six propagation equations are solved in their general form in a rectangular coordinate system. The noise directivity in the far field is calculated by applying an iteration scheme that finds the required radiation angles at the source resulting in propagation through a given observer point. Factors influencing the zone of silence are investigated. The caustics of geometrical acoustics and the exact locations where it forms is demonstrated by studying the variation in ray tube area obtained from transport equation. For a ring source convecting along the center-axis of an axisymmetric jet, the polar directivity of the radiated noise is obtained by an integration with respect to azimuthal directivity of compact quadrupole sources distributed on the ring. The Doppler factor is shown to vary slightly from point to point on the ring. Finally the scaling of the directivity pattern with power -3 of Doppler factor is investigated and compared with experimental data.

  19. Considerations on the acoustic energy radiated by toothed gears. [model for calculating noise intensity

    NASA Technical Reports Server (NTRS)

    Popinceanu, N. G.; Kremmer, I.

    1974-01-01

    A mechano-acoustic model is reported for calculating acoustic energy radiated by a working gear. According to this model, a gear is an acoustic coublet formed of the two wheels. The wheel teeth generate cylindrical acoustic waves while the front surfaces of the teeth behave like vibrating pistons. Theoretical results are checked experimentally and good agreement is obtained with open gears. The experiments show that the air noise effect is negligible as compared with the structural noise transmitted to the gear box.

  20. Real-time vehicle noise cancellation techniques for gunshot acoustics

    NASA Astrophysics Data System (ADS)

    Ramos, Antonio L. L.; Holm, Sverre; Gudvangen, Sigmund; Otterlei, Ragnvald

    2012-06-01

    Acoustical sniper positioning systems rely on the detection and direction-of-arrival (DOA) estimation of the shockwave and the muzzle blast in order to provide an estimate of a potential snipers location. Field tests have shown that detecting and estimating the DOA of the muzzle blast is a rather difficult task in the presence of background noise sources, e.g., vehicle noise, especially in long range detection and absorbing terrains. In our previous work presented in the 2011 edition of this conference we highlight the importance of improving the SNR of the gunshot signals prior to the detection and recognition stages, aiming at lowering the false alarm and miss-detection rates and, thereby, increasing the reliability of the system. This paper reports on real-time noise cancellation techniques, like Spectral Subtraction and Adaptive Filtering, applied to gunshot signals. Our model assumes the background noise as being short-time stationary and uncorrelated to the impulsive gunshot signals. In practice, relatively long periods without signal occur and can be used to estimate the noise spectrum and its first and second order statistics as required in the spectral subtraction and adaptive filtering techniques, respectively. The results presented in this work are supported with extensive simulations based on real data.

  1. Noise Levels in the Operating Room

    DTIC Science & Technology

    2001-10-01

    59-63. Hodge, B., & Thompson , J . F . (1990). Noise pollution in the operating theatre. The Lancet, 335, 891-894. Noise Levels 41...Kam, P. C. A., Kam A. C., & Thompson , J . F . (1994). Noise pollution in the anaesthetic and intensive care environment. Anaesthesia, 49, 982-986

  2. A Numerical Method of Calculating Propeller Noise Including Acoustic Nonlinear Effects

    NASA Technical Reports Server (NTRS)

    Korkan, K. D.

    1985-01-01

    Using the transonic flow fields(s) generated by the NASPROP-E computer code for an eight blade SR3-series propeller, a theoretical method is investigated to calculate the total noise values and frequency content in the acoustic near and far field without using the Ffowcs Williams - Hawkings equation. The flow field is numerically generated using an implicit three dimensional Euler equation solver in weak conservation law form. Numerical damping is required by the differencing method for stability in three dimensions, and the influence of the damping on the calculated acoustic values is investigated. The acoustic near field is solved by integrating with respect to time the pressure oscillations induced at a stationary observer location. The acoustic far field is calculated from the near field primitive variables as generated by NASPROP-E computer code using a method involving a perturbation velocity potential as suggested by Hawkings in the calculation of the acoustic pressure time-history at a specified far field observed location. the methodologies described are valid for calculating total noise levels and are applicable to any propeller geometry for which a flow field solution is available.

  3. Preliminary Analysis of Acoustic Measurements from the NASA-Gulfstream Airframe Noise Flight Test

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Lockhard, David D.; Humphreys, Willliam M.; Choudhari, Meelan M.; Van De Ven, Thomas

    2008-01-01

    The NASA-Gulfstream joint Airframe Noise Flight Test program was conducted at the NASA Wallops Flight Facility during October, 2006. The primary objective of the AFN flight test was to acquire baseline airframe noise data on a regional jet class of transport in order to determine noise source strengths and distributions for model validation. To accomplish this task, two measuring systems were used: a ground-based microphone array and individual microphones. Acoustic data for a Gulfstream G550 aircraft were acquired over the course of ten days. Over twenty-four test conditions were flown. The test matrix was designed to provide an acoustic characterization of both the full aircraft and individual airframe components and included cruise to landing configurations. Noise sources were isolated by selectively deploying individual components (flaps, main landing gear, nose gear, spoilers, etc.) and altering the airspeed, glide path, and engine settings. The AFN flight test program confirmed that the airframe is a major contributor to the noise from regional jets during landing operations. Sound pressure levels from the individual microphones on the ground revealed the flap system to be the dominant airframe noise source for the G550 aircraft. The corresponding array beamform maps showed that most of the radiated sound from the flaps originates from the side edges. Using velocity to the sixth power and Strouhal scaling of the sound pressure spectra obtained at different speeds failed to collapse the data into a single spectrum. The best data collapse was obtained when the frequencies were left unscaled.

  4. Noise in restaurants: levels and mathematical model.

    PubMed

    To, Wai Ming; Chung, Andy

    2014-01-01

    Noise affects the dining atmosphere and is an occupational hazard to restaurant service employees worldwide. This paper examines the levels of noise in dining areas during peak hours in different types of restaurants in Hong Kong SAR, China. A mathematical model that describes the noise level in a restaurant is presented. The 1-h equivalent continuous noise level (L(eq,1-h)) was measured using a Type-1 precision integral sound level meter while the occupancy density, the floor area of the dining area, and the ceiling height of each of the surveyed restaurants were recorded. It was found that the measured noise levels using Leq,1-h ranged from 67.6 to 79.3 dBA in Chinese restaurants, from 69.1 to 79.1 dBA in fast food restaurants, and from 66.7 to 82.6 dBA in Western restaurants. Results of the analysis of variance show that there were no significant differences between means of the measured noise levels among different types of restaurants. A stepwise multiple regression analysis was employed to determine the relationships between geometrical and operational parameters and the measured noise levels. Results of the regression analysis show that the measured noise levels depended on the levels of occupancy density only. By reconciling the measured noise levels and the mathematical model, it was found that people in restaurants increased their voice levels when the occupancy density increased. Nevertheless, the maximum measured hourly noise level indicated that the noise exposure experienced by restaurant service employees was below the regulated daily noise exposure value level of 85 dBA.

  5. The ecological and evolutionary consequences of noise-induced acoustic habitat loss

    NASA Astrophysics Data System (ADS)

    Tennessen, Jennifer Beissinger

    negative physiological consequences, and that populations have adapted over short timescales to minimize the detrimental impacts of this novel pressure. Finally, I present results from a field acoustic playback experiment that show that noise from the invasive Cuban treefrog (Osteopilus septentrionalis ) differentially affects the vocal behavior of native anurans, with those with more similar calls being disproportionally more affected. Green treefrogs (Hyla cinerea) shortened their calls, called louder, and maintained call spacing (e.g. continued actively calling) during noise stimuli whereas pine woods treefrogs (H. femoralis) did not modify vocal behavior in response to any noise stimuli. Collectively, the results of these investigations (1) provide insight into the extent of noise-induced acoustic habitat loss in space and time, (2) reveal fitness-relevant individual- and population-level consequences of this form of habitat loss, and (3) show resiliency within ecological systems through the individual- and population-level responses to this novel pressure over short time-scales. These findings advance the field by illustrating how the spatiotemporal extent of anthropogenic noise impacts important ecological processes, and by demonstrating the resiliency of some species in responding rapidly to novel pressures.

  6. Ocean Basin Impact of Ambient Noise on Marine Mammal Detectability, Distribution, and Acoustic Communication - YIP

    DTIC Science & Technology

    2013-09-30

    an additional southern hemisphere site for comparing noise trends to the Wake Island site in the northern hemisphere (Figure 1, Table 1). CTBTO...third- octave band sound levels over 42 months recorded at four deep-ocean observatories . Journal of Marine Systems (in press). Available online 29... European Conference on Underwater Acoustics 34: 1583- 1587. ISBN 978-1-906913-13-7. Hawkins RS, Miksis-Olds JL, Bradley DL and Smith CM (2012

  7. Effects of acoustic hood on noise, CFC-11, and particulate matter in a recycling system for waste refrigerator cabinet.

    PubMed

    Guo, Jie; Fang, Wenxiong; Yang, Yichen; Xu, Zhenming

    2014-11-01

    The mechanical-physical process was proven to be technologically feasible for waste refrigerator recycling and has been widely used in the typical e-waste recycling factories in China. In this study, effects of the acoustic hood on the reduction of noise level, CFC-11, and heavy metals (Cr, Ni, Cu, Cd, and Pb) in particulate matter (PM) were evaluated. For noise pollution, the noise level inside and outside the acoustic hood was 96.4 and 78.9 dB, respectively. Meanwhile, it had a significant effect on A-weighted sound level with a reduction from 98.3 to 63.6 dB. For CFC-11 exposure, abundant CFC-11 (255 mg/m(3)) was detected in the acoustic hood. However, the mean concentration of CFC-11 at the outline of polyurethane foam collection was obviously diminished to 14 mg/m(3), and no CFC-11 was monitored around the acoustic hood. The concentrations of PM and heavy metals in PM outside the acoustic hood were lower than those inside the acoustic hood due to the physical barriers of the acoustic hood. Based on the risk assessment, only adverse health effect caused by Pb might likely appear. All the results can provide the basic data for pollution control and risk assessment in waste refrigerator recycling system.

  8. On Acoustic Source Specification for Rotor-Stator Interaction Noise Prediction

    NASA Technical Reports Server (NTRS)

    Nark, Douglas M.; Envia, Edmane; Burley, Caesy L.

    2010-01-01

    This paper describes the use of measured source data to assess the effects of acoustic source specification on rotor-stator interaction noise predictions. Specifically, the acoustic propagation and radiation portions of a recently developed coupled computational approach are used to predict tonal rotor-stator interaction noise from a benchmark configuration. In addition to the use of full measured data, randomization of source mode relative phases is also considered for specification of the acoustic source within the computational approach. Comparisons with sideline noise measurements are performed to investigate the effects of various source descriptions on both inlet and exhaust predictions. The inclusion of additional modal source content is shown to have a much greater influence on the inlet results. Reasonable agreement between predicted and measured levels is achieved for the inlet, as well as the exhaust when shear layer effects are taken into account. For the number of trials considered, phase randomized predictions follow statistical distributions similar to those found in previous statistical source investigations. The shape of the predicted directivity pattern relative to measurements also improved with phase randomization, having predicted levels generally within one standard deviation of the measured levels.

  9. Noise-robust acoustic signature recognition using nonlinear Hebbian learning.

    PubMed

    Lu, Bing; Dibazar, Alireza; Berger, Theodore W

    2010-12-01

    We propose using a new biologically inspired approach, nonlinear Hebbian learning (NHL), to implement acoustic signal recognition in noisy environments. The proposed learning processes both spectral and temporal features of input acoustic data. The spectral analysis is realized by using auditory gammatone filterbanks. The temporal dynamics is addressed by analyzing gammatone-filtered feature vectors over multiple temporal frames, which is called a spectro-temporal representation (STR). Given STR features, the exact acoustic signatures of signals of interest and the mixing property between signals of interest and noises are generally unknown. The nonlinear Hebbian learning is then employed to extract representative independent features from STRs, and to reduce their dimensionality. The extracted independent features of signals of interest are called signatures. In the meantime of learning, the synaptic weight vectors between input and output neurons are adaptively updated. These weight vectors project data into a feature subspace, in which signals of interest are selected, while noises are attenuated. Compared with linear Hebbian learning (LHL) which explores the second-order moment of data, the applied NHL involves the higher-order statistics of data. Therefore, NHL can capture representative features that are more statistically independent than LHL can. Besides, the nonlinear activation function of NHL can be chosen to refer to the implicit distribution of many acoustic sounds, and thus making the learning optimized in an aspect of mutual information. Simulation results show that the whole proposed system can more accurately recognize signals of interest than other conventional methods in severely noisy circumstances. One applicable project is detecting moving vehicles. Noise-contaminated vehicle sound is recognized while other non-vehicle sounds are rejected. When vehicle is contaminated by human vowel, bird chirp, or additive white Gaussian noise (AWGN) at SNR=0

  10. Publications in acoustics and noise control from the NASA Langley Research Center during 1940-1976

    NASA Technical Reports Server (NTRS)

    Fryer, B. A. (Compiler)

    1977-01-01

    Reference lists are presented of published research papers in various areas of acoustics and noise control for the period 1940-1976. The references are listed chronologically and are grouped under the following general headings: (1) Duct acoustics; (2) propagation and operations; (3) rotating blade noise; (4) jet noise; (5) sonic boom; (6) flow-surface interaction noise; (7) human response; (8) structural response; (9) prediction; and (10) miscellaneous.

  11. Nuisance levels of noise effects radiologists' performance

    NASA Astrophysics Data System (ADS)

    McEntee, Mark F.; Coffey, Amina; Ryan, John; O'Beirne, Aaron; Toomey, Rachel; Evanoff, Micheal; Manning, David; Brennan, Patrick C.

    2010-02-01

    This study aimed to measure the sound levels in Irish x-ray departments. The study then established whether these levels of noise have an impact on radiologists performance Noise levels were recorded 10 times within each of 14 environments in 4 hospitals, 11 of which were locations where radiologic images are judged. Thirty chest images were then presented to 26 senior radiologists, who were asked to detect up to three nodular lesions within 30 posteroanterior chest x-ray images in the absence and presence of noise at amplitude demonstrated in the clinical environment. The results demonstrated that noise amplitudes rarely exceeded that encountered with normal conversation with the maximum mean value for an image-viewing environment being 56.1 dB. This level of noise had no impact on the ability of radiologists to identify chest lesions with figure of merits of 0.68, 0.69, and 0.68 with noise and 0.65, 0.68, and 0.67 without noise for chest radiologists, non-chest radiologists, and all radiologists, respectively. the difference in their performance using the DBM MRMC method was significantly better with noise than in the absence of noise at the 90% confidence interval (p=0.077). Further studies are required to establish whether other aspects of diagnosis are impaired such as recall and attention and the effects of more unexpected noise on performance.

  12. [Effect of noise on changes in the acoustic reflex].

    PubMed

    Zivić, Ljubica; Zivić, Djordje

    2003-01-01

    Acoustic, stapedial reflex represents a response of the m. stapedius to a sonic excitation of supra speech intensity. It is the constitutive part of impendancmetric investigations, it is performed on the same apparatus after tympanometry, and it is the inseparable part in representation of impendancmetric findings. Until now, the most frequently monitored parameters of acoustic reflex of clinical importance are: threshold, amplitude, output and input angle of the reflex curve. The aim of this work was to performed detailed analysis of mentioned parameters in workers exposed to extensive action of industrial noise of known physical characteristics (of different durations) and to establish which changes occurred in these workers, to what extent and under which conditions. Investigations included 173 industrial workers (346 ears), which work in working unit "Forge", where during the working process noise is produced which is above permissible limits and of the unfavorable frequency content. Workers were divided into two groups. The first group consisted of workers who were spending the whole working time in the workroom with noise above permissible limits, the second group consisted of workers who were spending 3 hours of the working time in that workroom, while the control group consisted of workers who were spending the whole working time in that workroom but they did not have any hearing impairment. Workers of the first and the second group had the hearing impairment, which occurred exclusively as a consequence of chronical acoustic trauma. For all the workers the anamnesis was taken, as well as ORL status and audiometric and impendancmetric investigations were performed, namely the tympanometry and acoustic reflex. Results have shown that the acoustic reflex threshold at 500 Hz and at 1000 Hz for the first group (95.10 dB) was increased with respect to the reflex threshold of the second and the control group (84 dB). At higher frequencies of 2000 Hz and 4000 Hz an

  13. Characterization of the Acoustic Field in Marine Environments with Anthropogenic Noise

    NASA Astrophysics Data System (ADS)

    Guan, Shane

    Most animals inhabit the aquatic environment are acoustical-oriented, due to the physical characteristics of water that favors sound transmission. Many aquatic animals depend on underwater sound to navigate, communicate, find prey, and avoid predators. The degradation of underwater acoustic environment due to human activities is expected to affected these animals' well-being and survival at the population level. This dissertation presents three original studies on the characteristics and behavior of underwater sound fields in three unique marine environments with anthropogenic noises. The first study examines the soundscape of the Chinese white dolphin habitat in Taiwan. Acoustic recordings were made at two coastal shallow water locations, Yunlin and Waisanding, in 2012. Results show that croaker choruses are dominant sound sources in the 1.2--2.4 kHz frequency band for both locations at night, and noises from container ships in the 150--300 Hz frequency band define the relative higher broadband sound levels at Yunlin. Results also illustrate interrelationships among different biotic, abiotic, and anthropogenic elements that shape the fine-scale soundscape in a coastal environment. The second study investigates the inter-pulse sound field during an open-water seismic survey in coastal shallow waters of the Arctic. The research uses continuous acoustic recordings collected from one bottom-mounted hydrophone deployed in the Beaufort Sea in summer 2012. Two quantitative methods were developed to examine the inter-pulse sound field characteristics and its dependence on source distances. Results show that inter-pulse sound field could raise the ambient noise floor by as much as 9 dB, depending on ambient condition and source distance. The third study examines the inter-ping sound field of simulated mid-frequency active sonar in deep waters off southern California in 2013 and 2014. The study used drifting acoustic recorder buoys to collect acoustic data during sonar

  14. Effects of Classroom Acoustics and Self-Reported Noise Exposure on Teachers' Well-Being

    ERIC Educational Resources Information Center

    Kristiansen, Jesper; Persson, Roger; Lund, Soren Peter; Shibuya, Hitomi; Nielsen, Per Moberg

    2013-01-01

    Beyond noise annoyance and voice problems, little is known about the effects that noise and poor classroom acoustics have on teachers' health and well-being. The aim of this field study was therefore to investigate the effects of perceived noise exposure and classroom reverberation on measures of well-being. Data on self-reported noise exposure,…

  15. Practical ranges of loudness levels of various types of environmental noise, including traffic noise, aircraft noise, and industrial noise.

    PubMed

    Salomons, Erik M; Janssen, Sabine A

    2011-06-01

    In environmental noise control one commonly employs the A-weighted sound level as an approximate measure of the effect of noise on people. A measure that is more closely related to direct human perception of noise is the loudness level. At constant A-weighted sound level, the loudness level of a noise signal varies considerably with the shape of the frequency spectrum of the noise signal. In particular the bandwidth of the spectrum has a large effect on the loudness level, due to the effect of critical bands in the human hearing system. The low-frequency content of the spectrum also has an effect on the loudness level. In this note the relation between loudness level and A-weighted sound level is analyzed for various environmental noise spectra, including spectra of traffic noise, aircraft noise, and industrial noise. From loudness levels calculated for these environmental noise spectra, diagrams are constructed that show the relation between loudness level, A-weighted sound level, and shape of the spectrum. The diagrams show that the upper limits of the loudness level for broadband environmental noise spectra are about 20 to 40 phon higher than the lower limits for narrowband spectra, which correspond to the loudness levels of pure tones. The diagrams are useful for assessing limitations and potential improvements of environmental noise control methods and policy based on A-weighted sound levels.

  16. Practical Ranges of Loudness Levels of Various Types of Environmental Noise, Including Traffic Noise, Aircraft Noise, and Industrial Noise

    PubMed Central

    Salomons, Erik M.; Janssen, Sabine A.

    2011-01-01

    In environmental noise control one commonly employs the A-weighted sound level as an approximate measure of the effect of noise on people. A measure that is more closely related to direct human perception of noise is the loudness level. At constant A-weighted sound level, the loudness level of a noise signal varies considerably with the shape of the frequency spectrum of the noise signal. In particular the bandwidth of the spectrum has a large effect on the loudness level, due to the effect of critical bands in the human hearing system. The low-frequency content of the spectrum also has an effect on the loudness level. In this note the relation between loudness level and A-weighted sound level is analyzed for various environmental noise spectra, including spectra of traffic noise, aircraft noise, and industrial noise. From loudness levels calculated for these environmental noise spectra, diagrams are constructed that show the relation between loudness level, A-weighted sound level, and shape of the spectrum. The diagrams show that the upper limits of the loudness level for broadband environmental noise spectra are about 20 to 40 phon higher than the lower limits for narrowband spectra, which correspond to the loudness levels of pure tones. The diagrams are useful for assessing limitations and potential improvements of environmental noise control methods and policy based on A-weighted sound levels. PMID:21776205

  17. Spin noise spectroscopy from acoustic to GHz frequencies

    NASA Astrophysics Data System (ADS)

    Hübner, Jens

    2010-03-01

    Performing perturbation free measurements on semiconductor quantum systems has long been banished to textbooks on quantum mechanics. The emergent technique of spin noise spectroscopy is challenging this restriction. Empowered only by the ever present intrinsic spin fluctuation dynamics in thermal equilibrium, spin noise spectroscopy is capable to directly deduce several physical properties of carriers spins in semiconductors from these fluctuations. Originating from spin noise measurements on alkali metal vapors in quantum optics [1] the method has become a powerful technique to unravel the intrinsic spin dynamics in semiconductors [2]. In this talk I will present the recent progress of spin noise spectroscopy and how it is used to monitor the spin dynamic in semiconductor quantum wells at thermal equilibrium and as a consequence thereof directly detect the spatial dynamics of the carriers being marked with their own spin on a microscopic scale [3]. Further I will present measurements of how the non-perturbative nature of spin noise spectroscopy gives valuable insight into the delicate dependence of the spin relaxation time of electrons on doping density and temperature in semiconductors n-doped in the vicinity of the metal-insulator transition where hyperfine and intra-band depolarization compete [4]. Also the measurement bandwidth can be extended to GHz frequencies by ultrafast optical probing [5] yielding in conjunction with depth resolved spin noise measurements insights into the origin of inhomogeneous spin dephasing effects at high magnetic fields [5]. Additionally I will present how spin noise spectroscopy can be employed to spatially depth resolve doping profiles with optical resolution [6] and give a summary on easy to implement techniques of spin noise spectroscopy at acoustic frequencies in alkali metal vapors. [4pt] [1] E. Aleksandrov and V. Zapassky, Zh. Eksp. Teor. Fiz. 81, 132 (1981); S. A. Crooker, D. G. Rickel, A. V. Balatsky, and D. L. Smith

  18. Acoustical and perceptual assessment of water sounds and their use over road traffic noise.

    PubMed

    Galbrun, Laurent; Ali, Tahrir T

    2013-01-01

    This paper examines physical and perceptual properties of water sounds generated by small to medium sized water features that have applications for road traffic noise masking. A large variety of water sounds were produced in the laboratory by varying design parameters. Analysis showed that estimations can be made on how these parameters affect sound pressure levels, frequency content, and psychoacoustic properties. Comparisons with road traffic noise showed that there is a mismatch between the frequency responses of traffic noise and water sounds, with the exception of waterfalls with high flow rates, which can generate large low frequency levels comparable to traffic noise. Perceptual assessments were carried out in the context of peacefulness and relaxation, where both water sounds and noise from dense road traffic were audible. Results showed that water sounds should be similar or not less than 3 dB below the road traffic noise level (confirming previous research), and that stream sounds tend to be preferred to fountain sounds, which are in turn preferred to waterfall sounds. Analysis made on groups of sounds also indicated that low sharpness and large temporal variations were preferred on average, although no acoustical or psychoacoustical parameter correlated well with the individual sound preferences.

  19. Acoustics of Jet Surface Interaction-Scrubbing Noise

    NASA Technical Reports Server (NTRS)

    Khavaran, Abbas

    2014-01-01

    Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity of the structure or embedded in the airframe. While such integrated systems are intended to shield noise from community, they also introduce new sources of sound. Sound generation due to interaction of a jet flow past a nearby solid surface is investigated here using the generalized acoustic analogy theory. The analysis applies to the boundary layer noise generated at and near a wall, and excludes the scattered noise component that is produced at the leading or the trailing edge. While compressibility effects are relatively unimportant at very low Mach numbers, frictional heat generation and thermal gradient normal to the surface could play important roles in generation and propagation of sound in high speed jets of practical interest. A general expression is given for the spectral density of the far field sound as governed by the variable density Pridmore-Brown equation. The propagation Greens function is solved numerically for a high aspect-ratio rectangular jet starting with the boundary conditions on the surface and subject to specified mean velocity and temperature profiles between the surface and the observer. It is shown the magnitude of the Greens function decreases with increasing source frequency andor jet temperature. The phase remains constant for a rigid surface, but varies with source location when subject to an impedance type boundary condition. The Greens function in the absence of the surface, and flight effect are also investigated.

  20. Acoustic Array Development for Wind Turbine Noise Characterization

    SciTech Connect

    Buck, S.; Roadman, J.; Moriarty, P.; Palo, S.

    2013-11-01

    This report discusses the design and use of a multi-arm, logarithmic spiral acoustic array by the National Renewable Energy Laboratory (NREL) for measurement and characterization of wind turbine-generated noise. The array was developed in collaboration with a team from the University of Colorado Boulder. This design process is a continuation of the elliptical array design work done by Simley. A description of the array system design process is presented, including array shape design, mechanical design, design of electronics and the data acquisition system, and development of post-processing software. System testing and calibration methods are detailed. Results from the initial data acquisition campaign are offered and discussed. Issues faced during this initial deployment of the array are presented and potential remedies discussed.

  1. Acoustic Noise Prediction of the Amine Swingbed ISS ExPRESS Rack Payload

    NASA Technical Reports Server (NTRS)

    Welsh, David; Smith, Holly; Wang, Shuo

    2010-01-01

    Acoustics plays a vital role in maintaining the health, safety, and comfort of crew members aboard the International Space Station (ISS). In order to maintain this livable and workable environment, acoustic requirements have been established to ensure that ISS hardware and payload developers account for the acoustic emissions of their equipment and develop acoustic mitigations as necessary. These requirements are verified by an acoustic emissions test of the integrated hardware. The Amine Swingbed ExPRESS (Expedite the PRocessing of ExperimentS to Space) rack payload creates a unique challenge to the developers in that the payload hardware is transported to the ISS in phases, making an acoustic emissions test on the integrated flight hardware impossible. In addition, the payload incorporates a high back pressure fan and a diaphragm vacuum pump, which are recognized as significant and complex noise sources. In order to accurately predict the acoustic emissions of the integrated payload, the individual acoustic noise sources and paths are first characterized. These characterizations are conducted though a series of acoustic emissions tests on the individual payload components. Secondly, the individual acoustic noise sources and paths are incorporated into a virtual model of the integrated hardware. The virtual model is constructed with the use of hybrid method utilizing the Finite Element Acoustic (FEA) and Statistical Energy Analysis (SEA) techniques, which predict the overall acoustic emissions. Finally, the acoustic model is validated though an acoustic characterization test performed on an acoustically similar mock-up of the flight unit. The results of the validated acoustic model are then used to assess the acoustic emissions of the flight unit and define further acoustic mitigation efforts.

  2. Channel noise enhances signal detectability in a model of acoustic neuron through the stochastic resonance paradigm.

    PubMed

    Liberti, M; Paffi, A; Maggio, F; De Angelis, A; Apollonio, F; d'Inzeo, G

    2009-01-01

    A number of experimental investigations have evidenced the extraordinary sensitivity of neuronal cells to weak input stimulations, including electromagnetic (EM) fields. Moreover, it has been shown that biological noise, due to random channels gating, acts as a tuning factor in neuronal processing, according to the stochastic resonant (SR) paradigm. In this work the attention is focused on noise arising from the stochastic gating of ionic channels in a model of Ranvier node of acoustic fibers. The small number of channels gives rise to a high noise level, which is able to cause a spike train generation even in the absence of stimulations. A SR behavior has been observed in the model for the detection of sinusoidal signals at frequencies typical of the speech.

  3. Weather observations through oceanic acoustic noise recorded by gliders

    NASA Astrophysics Data System (ADS)

    Cauchy, Pierre; Testor, Pierre; Guinet, Christophe; Gervaise, Cedric; Di Oro, Lucia; Ioana, Cornel; Mortier, Laurent; Bouin, Marie-Noelle; Beguery, Laurent; Klein, Patrice

    2013-04-01

    Offshore estimates of the meteorological parameters are unfortunately spurious when considering in-situ observtions only due to obvious observational limitations while their use would allow to calibrate satellite observations and to have better weather forecasts, if assimilated in numerical weather forecasting systems. The WOTAN (Weather Observations through Acoustic Noise) approach may be used to fill these gaps if coupled to the Global Ocean Observing Sytem which has now a global coverage thanks to many autonomous observing platforms. In this study we show first results from acoustic records collected by gliders deployed in the northwestern Mediterranean Sea in the framework of MOOSE. We show that using 3 descriptors at 5kHz, 8kHz, and 20kHz allows to extract the intensity of the wind and the precipitation when the glider is at depth. This approach based on the method presented by Barry & Nuysten (2004) is compared with meterological data from coastal weather stations and the offshore meteorological buoys from Meteo-France. We also show that there is a vane effect with the tail of the glider while at surface which allows to estimate the direction of the wind every so often. These observations coupled with the in-situ profiles on temperature and salinity profiles can allow to better study air-sea interactions.

  4. Adaptive Noise Reduction Techniques for Airborne Acoustic Sensors

    DTIC Science & Technology

    2012-01-01

    25 4.3 Super Kraft Monocoupe 90A RC airplane. . . . . . . . . . . . . . . . . . . . . . . 27 4.4 Access panel for fuselage of...begin clipping. This is an important consideration for airborne acoustic sensing, as the sound level aboard a UAV must not cause saturation of the...specifications of the Monocoupe used for this experiment are in Table 4.3. 26 Figure 4.3: Super Kraft Monocoupe 90A RC airplane. Figure 4.4: Access panel for

  5. Local oscillator phase noise limitation on the resolution of acoustic delay line wireless passive sensor measurement

    NASA Astrophysics Data System (ADS)

    Chrétien, N.; Friedt, J.-M.; Martin, G.

    2014-06-01

    The role of the phase noise of a local oscillator driving a pulsed-mode RADAR used for probing surface acoustic wave sensors is investigated. The echo delay, representative of the acoustic velocity, and hence the physical quantity probed by the sensor, is finely measured as a phase. Considering that the intrinsic oscillator phase fluctuation defines the phase noise measurement resolution, we experimentally and theoretically assess the relation between phase noise, measurement range, and measurand resolution.

  6. Background noise cancellation for improved acoustic detection of manatee vocalizations

    NASA Astrophysics Data System (ADS)

    Yan, Zheng; Niezrecki, Christopher; Beusse, Diedrich O.

    2005-06-01

    The West Indian manatee (Trichechus manatus latirostris) has become endangered partly because of an increase in the number of collisions with boats. A device to alert boaters of the presence of manatees, so that a collision can be avoided, is desired. A practical implementation of the technology is dependent on the hydrophone spacing and range of detection. These parameters are primarily dependent on the manatee vocalization strength, the decay of the signal's strength with distance, and the background noise levels. An efficient method to extend the detection range by using background noise cancellation is proposed in this paper. An adaptive line enhancer (ALE) that can detect and track narrow band signals buried in broadband noise is implemented to cancel the background noise. The results indicate that the ALE algorithm can efficiently extract the manatee calls from the background noise. The improved signal-to-noise ratio of the signal can be used to extend the range of detection of manatee vocalizations and reduce the false alarm and missing detection rate in their natural habitat. .

  7. Background noise cancellation for improved acoustic detection of manatee vocalizations

    NASA Astrophysics Data System (ADS)

    Yan, Zheng; Niezrecki, Christopher; Beusse, Diedrich O.

    2005-04-01

    The West Indian manatee (Trichechus manatus latirostris) has become endangered partly because of an increase in the number of collisions with boats. A device to alert boaters of the presence of manatees, so that a collision can be avoided, is desired. Practical implementation of the technology is dependent on the hydrophone spacing and range of detection. These parameters are primarily dependent on the manatee vocalization strength, the decay of the signal strength with distance, and the background noise levels. An efficient method to extend the detection range by using background noise cancellation is proposed in this paper. An adaptive line enhancer (ALE) that can detect and track narrowband signals buried in broadband noise is implemented to cancel the background noise. The results indicate that the ALE algorithm can efficiently extract the manatee calls from the background noise. The improved signal-to-noise ratio of the signal can be used to extend the range of detection of manatee vocalizations and reduce the false alarm and missing detection rate in their natural habitat.

  8. Initial Integration of Noise Prediction Tools for Acoustic Scattering Effects

    NASA Technical Reports Server (NTRS)

    Nark, Douglas M.; Burley, Casey L.; Tinetti, Ana; Rawls, John W.

    2008-01-01

    This effort provides an initial glimpse at NASA capabilities available in predicting the scattering of fan noise from a non-conventional aircraft configuration. The Aircraft NOise Prediction Program, Fast Scattering Code, and the Rotorcraft Noise Model were coupled to provide increased fidelity models of scattering effects on engine fan noise sources. The integration of these codes led to the identification of several keys issues entailed in applying such multi-fidelity approaches. In particular, for prediction at noise certification points, the inclusion of distributed sources leads to complications with the source semi-sphere approach. Computational resource requirements limit the use of the higher fidelity scattering code to predict radiated sound pressure levels for full scale configurations at relevant frequencies. And, the ability to more accurately represent complex shielding surfaces in current lower fidelity models is necessary for general application to scattering predictions. This initial step in determining the potential benefits/costs of these new methods over the existing capabilities illustrates a number of the issues that must be addressed in the development of next generation aircraft system noise prediction tools.

  9. Acoustic Barrier Facilitates Inlet Noise Measurements for Aft-Dominated Fans

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Noise levels for modern high-bypass-ratio subsonic turbofans tend to be aft dominated. That is, the highest flyover noise levels radiate from the fan exit. Measuring fan inlet sound radiation without aft radiation contamination requires selective suppression of the aft noise. In NASA Lewis Research Center's 9- by 15-Foot Low-Speed Wind Tunnel, an acoustic barrier was used to effectively isolate the inlet noise field for a model of an advanced turbofan. This proof-of-concept test was performed on a model turbofan manufactured for NASA Lewis by the Allison Engine Company as part of the Advanced Subsonic Technology program. The 8-cm-thick acoustic barrier was constructed in sections that were joined upon installation. These sections, which were composed of a wood frame with typically 0.64-cm tempered fiberboard skins, extended from the tunnel's floor to its ceiling and had an axial length of 61 cm. On the fan side of the barrier just downstream of the leading edge, the upstream section had an acoustic treatment--a bulk absorber with a perforated metal skin. It had a nominal full height and an axial length of 46 cm. In addition, an elliptical leading edge was faired into the upstream barrier section. The barrier was mounted on tracks on the tunnel floor and ceiling at a sideline distance of 15 cm from the fan nacelle. Tests were made with the barrier leading edge at the fan inlet highlight plane and 15 cm further aft. The barrier extended downstream essentially to the end of the treated tunnel test section.

  10. Noise generated by quiet engine fans. 2: Fan A. [measurement of power spectra and sideline perceived noise levels

    NASA Technical Reports Server (NTRS)

    Montegani, F. J.; Schaefer, J. W.; Stakolich, E. G.

    1974-01-01

    A significant effort within the NASA Quiet Engine Program has been devoted to acoustical evaluation at the Lewis Research Center noise test facility of a family of full-scale fans. This report, documents the noise results obtained with fan A - a 1.5-pressure-ratio, 1160-ft/sec-tip-speed fan. The fan is described and some aerodynamic operating data are given. Far-field noise around the fan was measured for a variety of configurations pertaining to acoustical treatment and over a range of operating conditions. Complete results of 1/3-octave band analysis of the data are presented in tabular form. Included also are power spectra and sideline perceived noise levels. Some representative 1/3-octave band data are presented graphically, and sample graphs of continuous narrow-band spectra are also provided.

  11. Acoustic noise generation by the DOE/NASA MOD-1 wind turbine

    NASA Technical Reports Server (NTRS)

    Kelley, N. D.

    1981-01-01

    The results of a series of measurements taken over the past year of the acoustic emissions from the DOE/NASA MOD-1 Wind Turbine show the maximum acoustic energy is concentrated in the low frequency range, often below 100 Hz. The temporal as well as the frequency characteristics of the turbine sounds have been shown to be important since the MOD-1 is capable of radiating both coherent and incoherent noise. The coherent sounds are usually impulsive and are manifested in an averaged frequency domain plot as large numbers of discrete energy bands extending from the blade passage frequency to beyond 50 Hz on occasion. It is these impulsive sounds which are identified as the principal source of the annoyance to a dozen families living within 3 km of the turbine. The source of the coherent noise appears to be the rapid, unsteady blade loads encountered as the blade passes through the wake of the tower structure. Annoying levels are occasionally reached at nearby homes due to the interaction of the low frequency, high energy peaks in the acoustic impulses and the structural modes of the homes as well as by direct radiation outdoors. The peak levels of these impulses can be enhanced or subdued through complete propagation.

  12. Fluids and Combustion Facility Acoustic Emissions Controlled by Aggressive Low-Noise Design Process

    NASA Technical Reports Server (NTRS)

    Cooper, Beth A.; Young, Judith A.

    2004-01-01

    The Fluids and Combustion Facility (FCF) is a dual-rack microgravity research facility that is being developed by Northrop Grumman Information Technology (NGIT) for the International Space Station (ISS) at the NASA Glenn Research Center. As an on-orbit test bed, FCF will host a succession of experiments in fluid and combustion physics. The Fluids Integrated Rack (FIR) and the Combustion Integrated Rack (CIR) must meet ISS acoustic emission requirements (ref. 1), which support speech communication and hearing-loss-prevention goals for ISS crew. To meet these requirements, the NGIT acoustics team implemented an aggressive low-noise design effort that incorporated frequent acoustic emission testing for all internal noise sources, larger-scale systems, and fully integrated racks (ref. 2). Glenn's Acoustical Testing Laboratory (ref. 3) provided acoustical testing services (see the following photograph) as well as specialized acoustical engineering support as part of the low-noise design process (ref. 4).

  13. Detection and classification of underwater targets in background noise acoustic daylight

    NASA Astrophysics Data System (ADS)

    Goo, Gee-In

    2003-09-01

    It has been reported that underwater target models, spheres and cylinders can be detected and classified in background acoustic noise. In this paper, the author presents his recent finding that underwater target is detectable in acoustic background noise in open waters. Using a resonance detection technique, G-Transform, the noise background of a number of AUTEC sample data files with mammal clicks were analyzed. From the noise backgrounds in these data files, a number of possible target signatures were observed. It suggests that real underwater targets may be detected and classified passively in background noise.

  14. Acoustic communication in two freshwater gobies: the relationship between ambient noise, hearing thresholds and sound spectrum.

    PubMed

    Lugli, M; Yan, H Y; Fine, M L

    2003-04-01

    Two freshwater gobies Padogobius martensii and Gobius nigricans live in shallow (5-70 cm) stony streams, and males of both species produce courtship sounds. A previous study demonstrated high noise levels near waterfalls, a quiet window in the noise around 100 Hz at noisy locations, and extremely short-range propagation of noise and goby signals. To investigate the relationship of this acoustic environment to communication, we determined audiograms for both species and measured parameters of courtship sounds produced in the streams. We also deflated the swimbladder in P. martensii to determine its effect on frequency utilization in sound production and hearing. Both species are maximally sensitive at 100 Hz and produce low-frequency sounds with main energy from 70 to 100-150 Hz. Swimbladder deflation does not affect auditory threshold or dominant frequency of courtship sounds and has no or minor effects on sound amplitude. Therefore, both species utilize frequencies for hearing and sound production that fall within the low-frequency quiet region, and the equivalent relationship between auditory sensitivity and maximum ambient noise levels in both species further suggests that ambient noise shapes hearing sensitivity.

  15. Characterizing response to elemental unit of acoustic imaging noise: an FMRI study.

    PubMed

    Tamer, Gregory G; Luh, Wen-Ming; Talavage, Thomas M

    2009-07-01

    Acoustic imaging noise produced during functional magnetic resonance imaging (fMRI) studies can hinder auditory fMRI research analysis by altering the properties of the acquired time-series data. Acoustic imaging noise can be especially confounding when estimating the time course of the hemodynamic response (HDR) in auditory event-related fMRI (fMRI) experiments. This study is motivated by the desire to establish a baseline function that can serve not only as a comparison to other quantities of acoustic imaging noise for determining how detrimental is one's experimental noise, but also as a foundation for a model that compensates for the response to acoustic imaging noise. Therefore, the amplitude and spatial extent of the HDR to the elemental unit of acoustic imaging noise (i.e., a single ping) associated with echoplanar acquisition were characterized and modeled. Results from this fMRI study at 1.5 T indicate that the group-averaged HDR in left and right auditory cortex to acoustic imaging noise (duration of 46 ms) has an estimated peak magnitude of 0.29% (right) to 0.48% (left) signal change from baseline, peaks between 3 and 5 s after stimulus presentation, and returns to baseline and remains within the noise range approximately 8 s after stimulus presentation.

  16. Noise disturbance in open-plan study environments: a field study on noise sources, student tasks and room acoustic parameters.

    PubMed

    Braat-Eggen, P Ella; van Heijst, Anne; Hornikx, Maarten; Kohlrausch, Armin

    2017-04-03

    The aim of this study is to gain more insight in the assessment of noise in open-plan study environments and to reveal correlations between noise disturbance experienced by students and the noise sources they perceive, the tasks they perform and the acoustic parameters of the open-plan study environment they work in. Data were collected in five open-plan study environments at universities in the Netherlands. A questionnaire was used to investigate student tasks, perceived sound sources and their perceived disturbance, and sound measurements were performed to determine the room acoustic parameters. This study shows that 38% of the surveyed students are disturbed by background noise in an open-plan study environment. Students are mostly disturbed by speech when performing complex cognitive tasks like studying for an exam, reading and writing. Significant but weak correlations were found between the room acoustic parameters and noise disturbance of students. Practitioner Summary: A field study was conducted to gain more insight in the assessment of noise in open-plan study environments at universities in the Netherlands. More than one third of the students was disturbed by noise. An interaction effect was found for task type, source type and room acoustic parameters.

  17. Influences of noise-interruption and information-bearing acoustic changes on understanding simulated electric-acoustic speech.

    PubMed

    Stilp, Christian; Donaldson, Gail; Oh, Soohee; Kong, Ying-Yee

    2016-11-01

    In simulations of electrical-acoustic stimulation (EAS), vocoded speech intelligibility is aided by preservation of low-frequency acoustic cues. However, the speech signal is often interrupted in everyday listening conditions, and effects of interruption on hybrid speech intelligibility are poorly understood. Additionally, listeners rely on information-bearing acoustic changes to understand full-spectrum speech (as measured by cochlea-scaled entropy [CSE]) and vocoded speech (CSECI), but how listeners utilize these informational changes to understand EAS speech is unclear. Here, normal-hearing participants heard noise-vocoded sentences with three to six spectral channels in two conditions: vocoder-only (80-8000 Hz) and simulated hybrid EAS (vocoded above 500 Hz; original acoustic signal below 500 Hz). In each sentence, four 80-ms intervals containing high-CSECI or low-CSECI acoustic changes were replaced with speech-shaped noise. As expected, performance improved with the preservation of low-frequency fine-structure cues (EAS). This improvement decreased for continuous EAS sentences as more spectral channels were added, but increased as more channels were added to noise-interrupted EAS sentences. Performance was impaired more when high-CSECI intervals were replaced by noise than when low-CSECI intervals were replaced, but this pattern did not differ across listening modes. Utilizing information-bearing acoustic changes to understand speech is predicted to generalize to cochlear implant users who receive EAS inputs.

  18. Lobed Mixer Design for Noise Suppression: Plume, Aerodynamic and Acoustic Data. Volume 2

    NASA Technical Reports Server (NTRS)

    Mengle, Vinod G.; Baker, V. David; Dalton, William N.; Bridges, James (Technical Monitor)

    2002-01-01

    A comprehensive database for the acoustic and aerodynamic characteristics of several model-scale lobe mixers of bypass ratio 5 to 6 has been created for mixed jet speeds up to 1080 ft per s at typical take-off (TO) conditions of small-to-medium turbofan engines. The flight effect was simulated for Mach numbers up to 0.3. The static thrust performance and plume data were also obtained at typical TO and cruise conditions. The tests were done at NASA Lewis anechoic dome and ASE's FluiDyne Laboratories. The effect of several lobe mixer and nozzle parameters, such as, lobe scalloping, lobe count, lobe penetration and nozzle length was examined in terms of flyover noise at constant altitude and also noise in the reference frame of the nozzle. This volume is divided into three parts: in the first two parts, we collate the plume survey data in graphical form (line, contour and surface plots) and analyze it; in part 3, we tabulate the aerodynamic data for the acoustics tests and the acoustic data in one-third octave band levels.

  19. Acoustic vector sensor beamforming reduces masking from underwater industrial noise during passive monitoring.

    PubMed

    Thode, Aaron M; Kim, Katherine H; Norman, Robert G; Blackwell, Susanna B; Greene, Charles R

    2016-04-01

    Masking from industrial noise can hamper the ability to detect marine mammal sounds near industrial operations, whenever conventional (pressure sensor) hydrophones are used for passive acoustic monitoring. Using data collected from an autonomous recorder with directional capabilities (Directional Autonomous Seafloor Acoustic Recorder), deployed 4.1 km from an arctic drilling site in 2012, the authors demonstrate how conventional beamforming on an acoustic vector sensor can be used to suppress noise arriving from a narrow sector of geographic azimuths. Improvements in signal-to-noise ratio of up to 15 dB are demonstrated on bowhead whale calls, which were otherwise undetectable using conventional hydrophones.

  20. Measurement and evaluation of the acoustic noise of a 3 Tesla MR scanner.

    PubMed

    Hattori, Yoko; Fukatsu, Hiroshi; Ishigaki, Takeo

    2007-01-01

    We measured the sound level and frequencies of the acoustic noise generated by a 3 Tesla (T) MR scanner, and investigated the subjective sound level for 30 healthy volunteers with either earplugs, headphones or both. The sound level of 3T was found to be higher than that of 1.5T in all sequences. The peak sound pressure level of 3T ranged from 125.7 dB for MR angiography to 130.7 dB for single shot EPI on the linear scale. The equivalent noise level was from 110.0 dB for FLAIR to 115.8 dB for T1-IR on the A-weighted scale, which exceeded 99 dB, the level regulated by the International Electrotechnical Commission (IEC). The study of the subjective sound level showed that the effect of noise reduction was not significantly different between earplugs and headphones. However, the use of both devices could reduce the subjective sound level significantly better than either one alone (P < 0.01). Thus we propose wearing both devices for ear-protection during 3T examinations.

  1. Numerical wave modelling for seismo-acoustic noise sources: wave model accuracy issues and evidence for variable seismic attenuation

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Lavanant, T.; Obrebski, M. J.; Marié, L.; Royer, J.

    2012-12-01

    Nonlinear wave-wave interactions generate noise that numerical ocean wave models may simulate. The accuracy of the noise source predicted by the theory of Longuet-Higgins (1950) and Hasselmann (1963) depends on the realism of the directional wave distribution, which is generally not very well known. Numerical noise models developed by Kedar et al. (2008) and Ardhuin et al. (2010) also suffer from poorly known seismic wave propagation and attenuation properties. Here, several seismic and ocean pressure records are used here to assess the effects of wave modelling errors on the magnitude of noise sources. Measurements within 200~m from the sea surface are dominated by acoustic-gravity modes, for which bottom effects are negligible. These data show that directional wave spectra are well enough reproduced to estimate seismo-acoustic noise sources at frequencies below 0.3~Hz, whith an underestimation of the noise level by about 50%. In larger water depths, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and Kerguelen islands reveal that a) deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, and is well predicted up to 0.4~Hz. b) In particular, evidence of the vertical modes expected theoretically is given by the local maxima in the noise spectrum. c) noise above 0.6 Hz is not well modeled probably due to a poor estimate of the directional properties of high frequency wind-waves, d) the noise level is strongly influenced by bottom properties, in particular the presence of sediments. Further, for continental coastal seismic stations, an accurate model of noise level variability near the noise spectral peak requires an accurate modelling of coastal reflection (Ardhuin and Roland JGR 2012). In cases where noise sources are confined to a small area (e.g. Obrebski et al. GRL 2012), the source amplitude may be factored out, allowing an estimate of seismic attenuation rates

  2. JAPE 91: Influence of terrain masking of the acoustic propagation of helicopter noise

    NASA Technical Reports Server (NTRS)

    Naz, P.

    1993-01-01

    The acoustic propagation in the case of a noise source masked by a small element of terrain has been investigated experimentally. These data have been measured during the 'terrain masking' experiment of the NATO JAPE 91 experimental campaign. The main objective of that experiment was to study the acoustic detection of a helicopter masked by a small hill. Microphones have been placed at different locations on the shadow zone of the hill to study the effect of the terrain obstruction on sound propagation. The results presented come from data measured by Atlas Elektronik and by ISL, and have been processed together. The terrain obstruction causes an excess attenuation of the SPL (Sound Pressure Level) for all the frequencies, but this attenuation is more effective for the high frequencies than for the low frequencies. Results typical of diffraction phenomena have been observed; the SPL is minimal at the foot of the hill and is relatively constant beyond it.

  3. Acoustic emissions of digital data video projectors- Investigating noise sources and their change during product aging

    NASA Astrophysics Data System (ADS)

    White, Michael Shane

    2005-09-01

    Acoustic emission testing continues to be a growing part of IT and telecommunication product design, as product noise is increasingly becoming a differentiator in the marketplace. This is especially true for digital/video display companies, such as InFocus Corporation, considering the market shift of these products to the home entertainment consumer as retail prices drop and performance factors increase. Projectors and displays using Digital Light Processing(tm) [DLP(tm)] technology incorporate a device known as a ColorWheel(tm) to generate the colors displayed at each pixel in the image. These ColorWheel(tm) devices spin at very high speeds and can generate high-frequency tones not typically heard in liquid crystal displays and other display technologies. Also, acoustic emission testing typically occurs at the beginning of product life and is a measure of acoustic energy emitted at this point in the lifecycle. Since the product is designed to be used over a long period of time, there is concern as to whether the acoustic emissions change over the lifecycle of the product, whether these changes will result in a level of nuisance to the average customer, and does this nuisance begin to develop prior to the intended lifetime of the product.

  4. Noise testing of an advanced design propeller in the Boeing transonic wind tunnel with and without test section acoustic treatment

    NASA Astrophysics Data System (ADS)

    Glover, B. M., Jr.; Plunkett, E. I.; Simcox, C. D.

    1984-10-01

    Noise tests using the NASA SR-6 advanced design propeller in the Boeing Transonic Wind Tunnel have recently been completed. Measurements were taken both with and without an acoustically treated test section. A wide range of helical tip speeds and power loadings were explored. Noise test techniques, previously not applied to advanced design propeller testing, have shown results indicating an increased level of confidence in the measured signatures. Typical results are presented along with recommendations for future noise tests and elementary empirical prediction methods for the SR-6.

  5. Location optimization of a long T-shaped acoustic resonator array in noise control of enclosures

    NASA Astrophysics Data System (ADS)

    Yu, Ganghua; Cheng, Li

    2009-11-01

    Acoustic resonators are widely used in various noise control applications. In the pursuit of better performance and broad band control, multiple resonators or a resonator array are usually needed. The interaction among resonators significantly impacts on the control performance and leads to the requirement for a systematic design tool to determine their locations. In this work, simulated annealing (SA) algorithm is employed to optimize the locations of a set of long T-shaped acoustic resonators (TARs) for noise control inside an enclosure. Multiple optimal configurations are shown to exist. The control performance in terms of sound pressure level reduction, however, seems to be independent of the initial resonator-locations. Optimal solutions obtained from the SA approach are shown to outperform other existing methods for a TAR array design. Numerical simulations are systematically verified by experiments. Optimal locations are then synthesized, leading to a set of criteria, applicable to the present configuration, to guide engineering applications. It is concluded that the proposed optimization approach provides a systematic and effective tool to optimize the locations of TARs in noise control inside enclosures.

  6. Effect of train type on annoyance and acoustic features of the rolling noise.

    PubMed

    Kasess, Christian H; Noll, Anton; Majdak, Piotr; Waubke, Holger

    2013-08-01

    This study investigated the annoyance associated with the rolling noise of different railway stock. Passbys of nine train types (passenger and freight trains) equipped with different braking systems were recorded. Acoustic features showed a clear distinction of the braking system with the A-weighted energy equivalent sound level (LAeq) showing a difference in the range of 10 dB between cast-iron braked trains and trains with disk or K-block brakes. Further, annoyance was evaluated in a psychoacoustic experiment where listeners rated the relative annoyance of the rolling noise for the different train types. Stimuli with and without the original LAeq differences were tested. For the original LAeq differences, the braking system significantly affected the annoyance with cast-iron brakes being most annoying, most likely as a consequence of the increased wheel roughness causing an increased LAeq. Contribution of the acoustic features to the annoyance was investigated revealing that the LAeq explained up to 94% of the variance. For the stimuli without differences in the LAeq, cast-iron braked train types were significantly less annoying and the spectral features explained up to 60% of the variance in the annoyance. The effect of these spectral features on the annoyance of the rolling noise is discussed.

  7. Relationship between container ship underwater noise levels and ship design, operational and oceanographic conditions

    PubMed Central

    McKenna, Megan F.; Wiggins, Sean M.; Hildebrand, John A.

    2013-01-01

    Low-frequency ocean ambient noise is dominated by noise from commercial ships, yet understanding how individual ships contribute deserves further investigation. This study develops and evaluates statistical models of container ship noise in relation to design characteristics, operational conditions, and oceanographic settings. Five-hundred ship passages and nineteen covariates were used to build generalized additive models. Opportunistic acoustic measurements of ships transiting offshore California were collected using seafloor acoustic recorders. A 5–10 dB range in broadband source level was found for ships depending on the transit conditions. For a ship recorded multiple times traveling at different speeds, cumulative noise was lowest at 8 knots, 65% reduction in operational speed. Models with highest predictive power, in order of selection, included ship speed, size, and time of year. Uncertainty in source depth and propagation affected model fit. These results provide insight on the conditions that produce higher levels of underwater noise from container ships.

  8. Timing vocal behavior: lack of temporal overlap avoidance to fluctuating noise levels in singing Eurasian wrens.

    PubMed

    Yang, Xiao-Jing; Slabbekoorn, Hans

    2014-10-01

    Many animals live in or near urban areas that have become increasingly widespread and noisy over the last century. Especially those species that rely heavily on acoustics for communication may be affected by these elevated anthropogenic noise levels. Many bird species that sing to defend their territories and to attract mates may have to exploit specific noise coping strategies to persist in such acoustically challenging conditions. Eurasian wrens (Troglodytes troglodytes), like several other bird species, have been shown in a previous experiment to time their vocalizations such that they avoid overlap with other singing birds. Here, we tested whether Eurasian wrens also time their songs to avoid overlap with fluctuating anthropogenic noise. However, we did not find any evidence in favor of this potential phenomenon. Territorial wrens persisted in singing without temporal adjustments in noisy territories with 'natural' fluctuations of traffic noise levels as well as during experimental exposure to intermittent white noise.

  9. System and method for characterizing voiced excitations of speech and acoustic signals, removing acoustic noise from speech, and synthesizing speech

    DOEpatents

    Burnett, Greg C.; Holzrichter, John F.; Ng, Lawrence C.

    2006-02-14

    The present invention is a system and method for characterizing human (or animate) speech voiced excitation functions and acoustic signals, for removing unwanted acoustic noise which often occurs when a speaker uses a microphone in common environments, and for synthesizing personalized or modified human (or other animate) speech upon command from a controller. A low power EM sensor is used to detect the motions of windpipe tissues in the glottal region of the human speech system before, during, and after voiced speech is produced by a user. From these tissue motion measurements, a voiced excitation function can be derived. Further, the excitation function provides speech production information to enhance noise removal from human speech and it enables accurate transfer functions of speech to be obtained. Previously stored excitation and transfer functions can be used for synthesizing personalized or modified human speech. Configurations of EM sensor and acoustic microphone systems are described to enhance noise cancellation and to enable multiple articulator measurements.

  10. System And Method For Characterizing Voiced Excitations Of Speech And Acoustic Signals, Removing Acoustic Noise From Speech, And Synthesizi

    DOEpatents

    Burnett, Greg C.; Holzrichter, John F.; Ng, Lawrence C.

    2006-04-25

    The present invention is a system and method for characterizing human (or animate) speech voiced excitation functions and acoustic signals, for removing unwanted acoustic noise which often occurs when a speaker uses a microphone in common environments, and for synthesizing personalized or modified human (or other animate) speech upon command from a controller. A low power EM sensor is used to detect the motions of windpipe tissues in the glottal region of the human speech system before, during, and after voiced speech is produced by a user. From these tissue motion measurements, a voiced excitation function can be derived. Further, the excitation function provides speech production information to enhance noise removal from human speech and it enables accurate transfer functions of speech to be obtained. Previously stored excitation and transfer functions can be used for synthesizing personalized or modified human speech. Configurations of EM sensor and acoustic microphone systems are described to enhance noise cancellation and to enable multiple articulator measurements.

  11. System and method for characterizing voiced excitations of speech and acoustic signals, removing acoustic noise from speech, and synthesizing speech

    DOEpatents

    Burnett, Greg C.; Holzrichter, John F.; Ng, Lawrence C.

    2004-03-23

    The present invention is a system and method for characterizing human (or animate) speech voiced excitation functions and acoustic signals, for removing unwanted acoustic noise which often occurs when a speaker uses a microphone in common environments, and for synthesizing personalized or modified human (or other animate) speech upon command from a controller. A low power EM sensor is used to detect the motions of windpipe tissues in the glottal region of the human speech system before, during, and after voiced speech is produced by a user. From these tissue motion measurements, a voiced excitation function can be derived. Further, the excitation function provides speech production information to enhance noise removal from human speech and it enables accurate transfer functions of speech to be obtained. Previously stored excitation and transfer functions can be used for synthesizing personalized or modified human speech. Configurations of EM sensor and acoustic microphone systems are described to enhance noise cancellation and to enable multiple articulator measurements.

  12. System and method for characterizing voiced excitations of speech and acoustic signals, removing acoustic noise from speech, and synthesizing speech

    DOEpatents

    Burnett, Greg C.; Holzrichter, John F.; Ng, Lawrence C.

    2006-08-08

    The present invention is a system and method for characterizing human (or animate) speech voiced excitation functions and acoustic signals, for removing unwanted acoustic noise which often occurs when a speaker uses a microphone in common environments, and for synthesizing personalized or modified human (or other animate) speech upon command from a controller. A low power EM sensor is used to detect the motions of windpipe tissues in the glottal region of the human speech system before, during, and after voiced speech is produced by a user. From these tissue motion measurements, a voiced excitation function can be derived. Further, the excitation function provides speech production information to enhance noise removal from human speech and it enables accurate transfer functions of speech to be obtained. Previously stored excitation and transfer functions can be used for synthesizing personalized or modified human speech. Configurations of EM sensor and acoustic microphone systems are described to enhance noise cancellation and to enable multiple articulator measurements.

  13. Industrial noise level study in a wheat processing factory in ilorin, nigeria

    NASA Astrophysics Data System (ADS)

    Ibrahim, I.; Ajao, K. R.; Aremu, S. A.

    2016-05-01

    An industrial process such as wheat processing generates significant noise which can cause adverse effects on workers and the general public. This study assessed the noise level at a wheat processing mill in Ilorin, Nigeria. A portable digital sound level meter HD600 manufactured by Extech Inc., USA was used to determine the noise level around various machines, sections and offices in the factory at pre-determined distances. Subjective assessment was also mode using a World Health Organization (WHO) standard questionnaire to obtain information regarding noise ratings, effect of noise on personnel and noise preventive measures. The result of the study shows that the highest noise of 99.4 dBA was recorded at a pressure blower when compared to other machines. WHO Class-4 hearing protector is recommended for workers on the shop floor and room acoustics should be upgraded to absorb some sounds transmitted to offices.

  14. Modification of computational auditory scene analysis (CASA) for noise-robust acoustic feature

    NASA Astrophysics Data System (ADS)

    Kwon, Minseok

    , the regulation of time constant update for filters in signal/control path as well as level-independent frequency glides with fixed frequency modulation. First, we scrutinized performance development in keyword recognition using the proposed methods in quiet and noise-corrupted environments. The results argue that multi-scale integration should be used along with CE in order to avoid ambiguous continuity in unvoiced segments. Moreover, the inclusion of the all modifications was observed to guarantee the noise-type-independent robustness particularly with severe interference. Moreover, the CASA with the auditory model was implemented into a single/dual-channel ASR using reference TIMIT corpus so as to get more general result. Hidden Markov model (HTK) toolkit was used for phone recognition in various environmental conditions. In a single-channel ASR, the results argue that unmasked acoustic features (unmasked GFCC) should combine with target estimates from the mask to compensate for missing information. From the observation of a dual-channel ASR, the combined GFCC guarantees the highest performance regardless of interferences within speech. Moreover, consistent improvement of noise robustness by GFCC (unmasked or combined) shows the validity of our proposed CASA implementation in dual microphone system. In conclusion, the proposed framework proves the robustness of the acoustic features in various background interferences via both direct distance evaluation and statistical assessment. In addition, the introduction of dual microphone system using the framework in this study shows the potential of the effective implementation of the auditory model-based CASA in ASR.

  15. Publications in acoustics and noise control from the NASA Langley Research Center during 1940 - 1974

    NASA Technical Reports Server (NTRS)

    Smith, G. C. (Compiler); Laneave, J. N. (Compiler)

    1975-01-01

    This document contains reference lists of published Langley Research Center papers in various areas of acoustics and noise control for the period 1940-1974. The research work was performed either in-house by the center staff or by other personnel supported entirely or in part by grants or contracts. The references are listed chronologically and are grouped under the following general headings: (1) Duct acoustics, (2) Propagation and operations, (3) Rotating blade noise, (4) Jet noise, (5) Sonic boom, (6) Flow-surface interaction noise, (7) Human response, and (8) Structural response.

  16. Noise levels associated with urban land use.

    PubMed

    King, Gavin; Roland-Mieszkowski, Marek; Jason, Timothy; Rainham, Daniel G

    2012-12-01

    Recent trends towards the intensification of urban development to increase urban densities and avoid sprawl should be accompanied by research into the potential for related health impacts from environmental exposure. The objective of the current study was to examine the effect of the built environment and land use on levels of environmental noise. Two different study areas were selected using a combination of small area census geography, land use information, air photography, and ground-truthing. The first study area represented residential land use and consisted of two- to three-story single-family homes. The second study area was characteristic of mixed-use urban planning with apartment buildings as well as commercial and institutional development. Study areas were subdivided into six grids, and a location was randomly selected within each grid for noise monitoring. Each location was sampled four times over a 24-h day, resulting in a total of 24 samples for each of the two areas. Results showed significant variability in noise within study areas and significantly higher levels of environmental noise in the mixed-use area. Both study areas exceeded recommended noise limits when evaluated against World Health Organization guidelines and yielded average noise events values in the moderate to serious annoyance range with the potential to obscure normal conversation and cause sleep disturbance.

  17. Measurement resolution of noise directivity patterns from acoustic flight tests

    NASA Technical Reports Server (NTRS)

    Conner, David A.

    1989-01-01

    The measurement resolution of noise directivity patterns from acoustic flight tests was investigated. Directivity angle resolution is affected by the data reduction parameters, the aircraft velocity and flyover altitude, and by deviations of the aircraft from the desired flight path. Equations are developed which determine bounds for the lateral and longitudinal directivity angle resolution as a function of the nominal directivity angle. The equations are applied to a flight test data base and the effects of several flight conditions and data reduction parameters on the directivity angle resolution are presented. The maximum directivity angle resolution typically occurs when the aircraft is at or near the overhead position. In general, directivity angle resolution improves with decreasing velocity, increasing altitude, increasing sampling rate, decreasing block size, and decreasing block averages. Deviations from the desired ideal flight path will increase the resolution. For the flight experiment considered in this study, an average of two flyovers were required at each test condition to obtain an acceptable flight path. The ability of the pilot to maintain the flight track improved with decreasing altitude, decreasing velocity, and practice. Due to the prevailing wind conditions, yaw angles of as much as 20 deg were required to maintain the desired flight path.

  18. Cylindrical acoustical holography applied to full-scale jet noise.

    PubMed

    Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; Krueger, David W; James, Michael M

    2014-09-01

    Near-field acoustical holography methods are used to predict sound radiation from an engine installed on a high-performance military fighter aircraft. Cylindrical holography techniques are an efficient approach to measure the large and complex sound fields produced by full-scale jets. It is shown that a ground-based, one-dimensional array of microphones can be used in conjunction with a cylindrical wave function field representation to provide a holographic reconstruction of the radiated sound field at low frequencies. In the current work, partial field decomposition methods and numerical extrapolation of data beyond the boundaries of the hologram aperture are required prior to holographic projection. Predicted jet noise source distributions and directionality are shown for four frequencies between 63 and 250 Hz. It is shown that the source distribution narrows and moves upstream, and that radiation directionality shifts toward the forward direction, with increasing frequency. A double-lobe feature of full-scale jet radiation is also demonstrated.

  19. Acoustic isolation vessel for measurement of the background noise in microphones

    NASA Technical Reports Server (NTRS)

    Ngo, Kim C. T.; Zuckerwar, Allan J.

    1993-01-01

    An acoustic isolation vessel has been developed to measure the background noise in microphones. The test microphone is installed in an inner vessel, which is suspended within an outer vessel, and the intervening air space is evacuated to a high vacuum. An analytical expression for the transmission coefficient is derived, based on a five-media model, and compared to experiment. At an isolation vacuum of 5 x 10 exp -6 Torr the experimental transmission coefficient was found to be lower than -155 dB at frequencies ranging from 40 to 1200 Hz. Measurements of the A-weighted noise levels of commercial condenser microphones of four different sizes show good agreement with published values.

  20. Noise control for a ChamberCore cylindrical structure using long T-shaped acoustic resonators

    NASA Astrophysics Data System (ADS)

    Li, Deyu; Vipperman, Jeffrey S.

    2003-10-01

    The Air Force Research Laboratory, Space Vehicles Directorate has developed a new advanced composite launch vehicle fairing (referred to as ``ChamberCore''). The ChamberCore is sandwich-type structure fabricated from multi-layered composite face sheets separated by channels that form passive acoustic chambers. These acoustic chambers have a potential to create an acoustic resonator network that can be used to attenuate noise inside the closed ChamberCore cylindrical structure. In this study, first, the feasibility of using cylindrical Helmholtz resonators to control noise in a mock-scale ChamberCore composite cylinder is investigated. The targeted frequencies for noise control are the first four acoustic cavity resonances of the ChamberCore cylinder. The optimal position of the Helmholtz resonators for controlling each targeted cavity mode is discussed, and the effects of resonator spacing on noise attenuation are also experimentally evaluated. Next, six long T-shaped acoustic resonators are designed and constructed within the acoustic chambers of the structure and investigated. Several tests are conducted to evaluate the noise control ability of the resonators in the ChamberCore cylinder. Reductions ranging from 3.2 to 6.0 dB were observed in the overall mean-square noise reduction spectrum at the targeted inner cavity resonance frequencies. [Work supported by AFRL/DV.

  1. A comparison of linear acoustic theory with experimental noise data for a small-scale hovering rotor

    NASA Technical Reports Server (NTRS)

    Farassat, F.; Morris, C. E. K., Jr.; Nystrom, P. A.

    1979-01-01

    Linear acoustic calculations based on full aerodynamic data as input are presented and compared with measured cases reported by Boxwell et al. (1978). The full aerodynamic data are obtained using three programs giving radial loading, chordwise loading, and chordwise position of transition. It is shown that in the theoretical results the most significant noise source mechanism is due to blade thickness. Thus the conclusions of Boxwell et al. as to the importance of nonlinearities around the blades are upheld. These conclusions concern the width, shape and the level of the acoustic pressure calculated from linear acoustic theory. Some of the approximations involved in the application of acoustic analogy using quadrupole sources are discussed. It is necessary that the near- and far-field problems of rotating blades be treated together as shown for the case of an oscillating sphere.

  2. Acoustic Noise Removal by Combining Wiener and Wavelet Filtering Techniques

    DTIC Science & Technology

    1998-06-01

    Noise 7 B. TRANSMISSION LOSS AND WATER MASS CHARACTERISTICS 8 C. NOISE MODEL 8 m. WIENER FILTERING 11 A. MODEL DESCRIPTION 11 B. FIR WIENER...measurements in this band in deep, quiet open ocean water appear to have been made until now. 2. Self Noise Self noise includes all noise created by...all- water direct path, all- water back scattered path from volume scatterers, and all- water bottom reflected path [2]. Machinery noise occurs

  3. The Uses and Abuses of the Acoustic Analogy in Helicopter Rotor Noise Prediction

    NASA Technical Reports Server (NTRS)

    Farassat, F.; Brentner, Kenneth S.

    1987-01-01

    This paper is theoretical in nature and addresses applications of the acoustic analogy in helicopter rotor noise prediction. It is argued that in many instances the acoustic analogy has not been used with care in rotor noise studies. By this it is meant that approximate or inappropriate formulations have been used. By considering various mechanisms of noise generation, such abuses are identified and the remedy is suggested. The mechanisms discussed are thickness, loading, quadrupole, and blade-vortex interaction noise. The quadrupole term of the Ffowcs Williams-Hawkings equation is written in a new form which separates the contributions of regions of high gradients such as shock surfaces. It is shown by order of magnitude studies that such regions are capable of producing noise with the same directivity as the thickness noise. The inclusion of this part of quadrupole sources in current acoustic codes is quite practical. Some of the difficulties with the use of loading noise formulations of the first author in predictions of blade-vortex interaction noise are discussed. It appears that there is a need for development of new theoretical results based on the acoustic analogy in this area. Because of the impulsive character of the blade surface pressure, a time scale of integration different from that used in loading and thickness computations must he used in a computer code for prediction of blade-vortex interaction noise.

  4. Noise measurements on the helicopter BK 117 design. Weighted noise levels and influence of airspeed

    NASA Astrophysics Data System (ADS)

    Splettstoesser, Wolf R.; Anders, Klaus P.; Spiegel, Karl-Heinz

    1986-11-01

    Noise measurements on the prototype helicopter BK 117 were performed in strict compliance with the proposed international Civil Aviation Organization regulations for noise certification of helicopters. Measurement procedure, noise data acquisition, analysis and reduction as well as applied correction procedures are described. Effective perceived noise levels (EPNL) and other noise descriptors were evaluated and related to the proposed noise limits. Additional level flyover tests with variable airspeed were conducted to investigate the resulting effect on the EPNL and other noise measures.

  5. Lobed Mixer Design for Noise Suppression Acoustic and Aerodynamic Test Data Analysis

    NASA Technical Reports Server (NTRS)

    Mengle, Vinod G.; Dalton, William N.; Boyd, Kathleen (Technical Monitor); Bridges, James (Technical Monitor)

    2002-01-01

    A comprehensive database for the acoustic and aerodynamic characteristics of several model-scale lobe mixers of bypass ratio 5 to 6 has been created for mixed jet speeds up to 1080 ft/s at typical take-off (TO) conditions of small-to-medium turbofan engines. The flight effect was simulated for Mach numbers up to 0.3. The static thrust performance and plume data were also obtained at typical TO and cruise conditions. The tests were done at NASA Lewis anechoic dome and ASK's FluiDyne Laboratories. The effect of several lobe mixer and nozzle parameters, such as, lobe scalloping, lobe count, lobe penetration and nozzle length was examined in terms of flyover noise at constant altitude. Sound in the nozzle reference frame was analyzed to understand the source characteristics. Several new concepts, mechanisms and methods are reported for such lobed mixers, such as, "boomerang" scallops, "tongue" mixer, detection of "excess" internal noise sources, and extrapolation of flyover noise data from one flight speed to different flight speeds. Noise reduction of as much as 3 EPNdB was found with a deeply scalloped mixer compared to annular nozzle at net thrust levels of 9500 lb for a 29 in. diameter nozzle after optimizing the nozzle length.

  6. Acoustical and Perceptual Comparison of Noise Reduction and Compression in Hearing Aids

    ERIC Educational Resources Information Center

    Brons, Inge; Houben, Rolph; Dreschler, Wouter A.

    2015-01-01

    Purpose: Noise reduction and dynamic-range compression are generally applied together in hearing aids but may have opposite effects on amplification. This study evaluated the acoustical and perceptual effects of separate and combined processing of noise reduction and compression. Design: Recordings of the output of 4 hearing aids for speech in…

  7. Noise levels in the learning-teaching activities in a dental medicine school

    NASA Astrophysics Data System (ADS)

    Matos, Andreia; Carvalho, Antonio P. O.; Fernandes, Joao C. S.

    2002-11-01

    The noise levels made by different clinical handpieces and laboratory engines are considered to be the main descriptors of acoustical comfort in learning spaces in a dental medicine school. Sound levels were measured in five types of classrooms and teaching laboratories at the University of Porto Dental Medicine School. Handpiece noise measurements were made while instruments were running free and during operations with cutting tools (tooth, metal, and acrylic). Noise levels were determined using a precision sound level meter, which was positioned at ear level and also at one-meter distance from the operator. Some of the handpieces were brand new and the others had a few years of use. The sound levels encountered were between 60 and 99 dB(A) and were compared with the noise limits in A-weighted sound pressure level for mechanical equipments installed in educational buildings included in the Portuguese Noise Code and in other European countries codes. The daily personal noise exposure levels (LEP,d) of the students and professors were calculated to be between 85 and 90 dB(A) and were compared with the European legal limits. Some noise limits for this type of environment are proposed and suggestions for the improvement of the acoustical environment are given.

  8. Computational Acoustic Beamforming for Noise Source Identification for Small Wind Turbines

    PubMed Central

    Lien, Fue-Sang

    2017-01-01

    This paper develops a computational acoustic beamforming (CAB) methodology for identification of sources of small wind turbine noise. This methodology is validated using the case of the NACA 0012 airfoil trailing edge noise. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of noise sources generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz. PMID:28378012

  9. Computational Acoustic Beamforming for Noise Source Identification for Small Wind Turbines.

    PubMed

    Ma, Ping; Lien, Fue-Sang; Yee, Eugene

    2017-01-01

    This paper develops a computational acoustic beamforming (CAB) methodology for identification of sources of small wind turbine noise. This methodology is validated using the case of the NACA 0012 airfoil trailing edge noise. For this validation case, the predicted acoustic maps were in excellent conformance with the results of the measurements obtained from the acoustic beamforming experiment. Following this validation study, the CAB methodology was applied to the identification of noise sources generated by a commercial small wind turbine. The simulated acoustic maps revealed that the blade tower interaction and the wind turbine nacelle were the two primary mechanisms for sound generation for this small wind turbine at frequencies between 100 and 630 Hz.

  10. A noise level prediction method based on electro-mechanical frequency response function for capacitors.

    PubMed

    Zhu, Lingyu; Ji, Shengchang; Shen, Qi; Liu, Yuan; Li, Jinyu; Liu, Hao

    2013-01-01

    The capacitors in high-voltage direct-current (HVDC) converter stations radiate a lot of audible noise which can reach higher than 100 dB. The existing noise level prediction methods are not satisfying enough. In this paper, a new noise level prediction method is proposed based on a frequency response function considering both electrical and mechanical characteristics of capacitors. The electro-mechanical frequency response function (EMFRF) is defined as the frequency domain quotient of the vibration response and the squared capacitor voltage, and it is obtained from impulse current experiment. Under given excitations, the vibration response of the capacitor tank is the product of EMFRF and the square of the given capacitor voltage in frequency domain, and the radiated audible noise is calculated by structure acoustic coupling formulas. The noise level under the same excitations is also measured in laboratory, and the results are compared with the prediction. The comparison proves that the noise prediction method is effective.

  11. Manatee (Trichechus manatus) vocalization usage in relation to environmental noise levels.

    PubMed

    Miksis-Olds, Jennifer L; Tyack, Peter L

    2009-03-01

    Noise can interfere with acoustic communication by masking signals that contain biologically important information. Communication theory recognizes several ways a sender can modify its acoustic signal to compensate for noise, including increasing the source level of a signal, its repetition, its duration, shifting frequency outside that of the noise band, or shifting the timing of signal emission outside of noise periods. The extent to which animals would be expected to use these compensation mechanisms depends on the benefit of successful communication, risk of failure, and the cost of compensation. Here we study whether a coastal marine mammal, the manatee, can modify vocalizations as a function of behavioral context and ambient noise level. To investigate whether and how manatees modify their vocalizations, natural vocalization usage and structure were examined in terms of vocalization rate, duration, frequency, and source level. Vocalizations were classified into two call types, chirps and squeaks, which were analyzed independently. In conditions of elevated noise levels, call rates decreased during feeding and social behaviors, and the duration of each call type was differently influenced by the presence of calves. These results suggest that ambient noise levels do have a detectable effect on manatee communication and that manatees modify their vocalizations as a function of noise in specific behavioral contexts.

  12. Background noise levels and correlation with ship traffic in the Gulf of Catania

    NASA Astrophysics Data System (ADS)

    Viola, Salvatore; Buscaino, Giuseppa; Caruso, Francesco; Chierici, Francesco; Embriaco, Davide; Favali, Paolo; Giovanetti, Gabriele; Grammauta, Roasario; Larosa, Giuseppina; Pavan, Gianni; Pellegrino, Carmelo; Pulvirenti, Sara; Riccobene, Giorgio; Sciacca, Virginia; Simeone, Francesco; Beranzoli, Laura; Marinaro, Giuditta

    2015-04-01

    In the last decades the growing interest in the evaluation of the underwater acoustic noise for studies in the fields of geology, biology and high-energy physics is driving the scientific community to collaborate towards a multidisciplinary approach to the topic. In June 2012 in the framework of the European project EMSO, a multidisciplinary underwater observatory, named NEMO-SN1, was installed 25 km off-shore the port of Catania, at a depth of 2100 m and operated until May 2013 by INFN (Istituto Nazionale di Fisica Nucleare) and INGV (Istituto Nazionale di Geofisica e Vulcanologia). NEMO-SN1 hosted aboard geophysical, oceanographic and acoustic sensors: among these a seismic hydrophone model SMID DT-405D(V). In this work, conducted within the activity of the SMO project, the results on the evaluation of the underwater acoustic pollution in the Gulf of Catania through SMID DT-405D(V) recordings are presented. The seismic hydrophone provided a data set of about 11 months of continuous (24/7) recordings. Underwater sounds have been continuously digitized at a sampling frequency of 2 kHz and the acquired data have been stored in 10min long files for off-line analysis. To describe one-year background noise levels, the mean integrated acoustic noise was measured every second (sampling frequency 2000, NFFT 2048) in the 1/3 octave bands with centre frequency 63 Hz and for each 10 minutes-long file the 5th, the 50th and the 98th percentiles were calculated. Measured noise was correlated with the shipping traffic in the area, thanks to the data provided by an AIS receiver installed at the INFN-Laboratori Nazionali del Sud. An acoustic noise increment was measured in coincidence with the passing of crafts in the area and it was possible to identify the characteristic spectrum of each ship. A simple model for the estimation of the acoustic noise induced by the ships passing through the area was developed. The model was applied by using AIS data acquired during the operation

  13. High Frequency Acoustic Channel Characterization for Propagation and Ambient Noise

    DTIC Science & Technology

    2008-09-30

    has done in close collaboration with Michael Porter and Paul Hursky (HLS Research) also supported by ONR. We have also been collaborating with Steve... Michael Porter , “A passive fathometer technique for imaging seabed layering using ambient noise”, J. Acoust. Soc. Am., 120, 1315-1323, (September...Siderius and Michael Porter , “Modeling broadband ocean acoustic transmissions with time- varying sea surfaces”, J. Acoust. Soc. Am., 124 (1), 137-150

  14. Passive acoustic observations of tide height in the Iroise Sea using ambient noise.

    PubMed

    Kinda, G Bazile; Bonnel, Julien

    2015-09-01

    Considering a broadband motionless source in a waveguide with a depth that varies with time, the time-frequency representation of the acoustic intensity shows a striation pattern than can be explained using the depth-frequency waveguide invariant. This phenomenon is used here to describe acoustic data recorded in the Iroise Sea, where intense tides occur. The originality of this study is that the acoustic data consist of only ambient noise. The best hypothesis is that these striations are created by distant marine traffic in the Bay of Brest, and the results suggest that tide height can be monitored using long-term passive acoustics.

  15. A First Look at the DGEN380 Engine Acoustic Data from a Core-Noise Perspective

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.

    2015-01-01

    This work is a first look at acoustic data acquired in the NASA Glenn Research Center Aero-Acoustic Propulsion Laboratory using the Price Induction DGEN380 small turbofan engine, with particular emphasis on broadband combustor (core) noise. Combustor noise is detected by using a two-signal source separation technique employing one engine-internal sensor and one semi-far-field microphone. Combustor noise is an important core-noise component and is likely to become a more prominent contributor to overall airport community noise due to turbofan design trends, expected aircraft configuration changes, and advances in fan-noise-mitigation techniques. This work was carried out under the NASA Fundamental Aeronautics Program, Fixed Wing Project, Quiet Performance Subproject

  16. Noise levels of dental equipment used in dental college of Damascus University

    PubMed Central

    Qsaibati, Mhd. Loutify; Ibrahim, Ousama

    2014-01-01

    Background: In dental practical classes, the acoustic environment is characterized by high noise levels in relation to other teaching areas. The aims of this study were to measure noise levels produced during the different dental learning clinics, by equipments used in dental learning areas under different working conditions and by used and brand new handpieces under different working conditions. Materials and Methods: The noise levels were measured by using a noise level meter with a microphone, which was placed at a distance of 15 cm from a main noise source in pre-clinical and clinical areas. In laboratories, the microphone was placed at a distance of 15 cm and another reading was taken 2 m away. Noise levels of dental learning clinics were measured by placing noise level meter at clinic center. The data were collected, tabulated and statistically analyzed using t-tests. Significance level was set at 5%. Results: In dental clinics, the highest noise was produced by micro motor handpiece while cutting on acrylic (92.2 dB) and lowest noise (51.7 dB) was created by ultrasonic scaler without suction pump. The highest noise in laboratories was caused by sandblaster (96 dB at a distance of 15 cm) and lowest noise by stone trimmer when only turned on (61.8 dB at a distance of 2 m). There was significant differences in noise levels of the equipment's used in dental laboratories and dental learning clinics (P = 0.007). The highest noise level recorded in clinics was at pedodontic clinic (67.37 dB). Conclusions: Noise levels detected in this study were considered to be close to the limit of risk of hearing loss 85 dB. PMID:25540655

  17. Noise control using a plate radiator and an acoustic resonator

    NASA Technical Reports Server (NTRS)

    Pla, Frederic G. (Inventor)

    1996-01-01

    An active noise control subassembly for reducing noise caused by a source (such as an aircraft engine) independent of the subassembly. A noise radiating panel is bendably vibratable to generate a panel noise canceling at least a portion of the source noise. A piezoceramic actuator plate is connected to the panel. A front plate is spaced apart from the panel and the first plate, is positioned generally between the source noise and the panel, and has a sound exit port. A first pair of spaced-apart side walls each generally abut the panel and the front plate so as to generally enclose a front cavity to define a resonator.

  18. Numerical Comparison of Active Acoustic and Structural Noise Control in a Stiffened Double Wall Cylinder

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.

    1996-01-01

    The active acoustic and structural noise control characteristics of a double wall cylinder with and without ring stiffeners were numerically evaluated. An exterior monopole was assumed to acoustically excite the outside of the double wall cylinder at an acoustic cavity resonance frequency. Structural modal vibration properties of the inner and outer shells were analyzed by post-processing the results from a finite element analysis. A boundary element approach was used to calculate the acoustic cavity response and the coupled structural-acoustic interaction. In the frequency region of interest, below 500 Hz, all structural resonant modes were found to be acoustically slow and the nonresonant modal response to be dominant. Active sound transmission control was achieved by control forces applied to the inner or outer shell, or acoustic control monopoles placed just outside the inner or outer shell. A least mean square technique was used to minimize the interior sound pressures at the nodes of a data recovery mesh. Results showed that single acoustic control monopoles placed just outside the inner or outer shells resulted in better sound transmission control than six distributed point forces applied to either one of the shells. Adding stiffeners to the double wall structure constrained the modal vibrations of the shells, making the double wall stiffer with associated higher modal frequencies. Active noise control obtained for the stiffened double wall configurations was less than for the unstiffened cylinder. In all cases, the acoustic control monopoles controlled the sound transmission into the interior better than the structural control forces.

  19. Sediment Acoustics: Wideband Model, Reflection Loss and Ambient Noise Inversion

    DTIC Science & Technology

    2011-09-01

    grain contact in water- saturated sand," J. Acoust. Soc. Am., vol. 124, pp. EL296-301, (2008). N. P. Chotiros, and M. J. Isakson. "Shear and...34Frame bulk modulus of porous granular marine sediments," J. Acoust. Soc. Am. 120, 699-710, (2006). B. J. Kraft and C. P. de Moustier, "Detailed

  20. Beaked whale (Mesoplodon densirostris) passive acoustic detection in increasing ambient noise.

    PubMed

    Ward, Jessica; Jarvis, Susan; Moretti, David; Morrissey, Ronald; Dimarzio, Nancy; Johnson, Mark; Tyack, Peter; Thomas, Len; Marques, Tiago

    2011-02-01

    Passive acoustic detection is being increasingly used to monitor visually cryptic cetaceans such as Blainville's beaked whales (Mesoplodon densirostris) that may be especially sensitive to underwater sound. The efficacy of passive acoustic detection is traditionally characterized by the probability of detecting the animal's sound emissions as a function of signal-to-noise ratio. The probability of detection can be predicted using accepted, but not necessarily accurate, models of the underwater acoustic environment. Recent field studies combining far-field hydrophone arrays with on-animal acoustic recording tags have yielded the location and time of each sound emission from tagged animals, enabling in-situ measurements of the probability of detection. However, tagging studies can only take place in calm seas and so do not reflect the full range of ambient noise conditions under which passive acoustic detection may be used. Increased surface-generated noise from wind and wave interaction degrades the signal-to-noise ratio of animal sound receptions at a given distance leading to a reduction in probability of detection. This paper presents a case study simulating the effect of increasing ambient noise on detection of M. densirostris foraging clicks recorded from a tagged whale swimming in the vicinity of a deep-water, bottom-mounted hydrophone array.

  1. Experimental investigation of shock-cell noise reduction for dual-stream nozzles in simulated flight comprehensive data report. Volume 1: Test nozzles and acoustic data

    NASA Technical Reports Server (NTRS)

    Yamamoto, K.; Janardan, B. A.; Brausch, J. F.; Hoerst, D. J.; Price, A. O.

    1984-01-01

    Parameters which contribute to supersonic jet shock noise were investigated for the purpose of determining means to reduce such noise generation to acceptable levels. Six dual-stream test nozzles with varying flow passage and plug closure designs were evaluated under simulated flight conditions in an anechoic chamber. All nozzles had combined convergent-divergent or convergent flow passages. Acoustic behavior as a function of nozzle flow passage geometry was measured. The acoustic data consist primarily of 1/3 octave band sound pressure levels and overall sound pressure levels. Detailed schematics and geometric characteristics of the six scale model nozzle configurations and acoustic test point definitions are presented. Tabulation of aerodynamic test conditions and a computer listing of the measured acoustic data are displayed.

  2. Experimental study of coaxial nozzle exhaust noise. [acoustic measurements

    NASA Technical Reports Server (NTRS)

    Goodykoontz, J. H.; Stone, J. R.

    1979-01-01

    Experimental results are presented for static acoustic model tests of various geometrical configurations of coaxial nozzles operating over a range of flow conditions. The geometrical configurations consisted of nozzles with coplanar and non-coplanar exit planes and various exhaust area ratios. Primary and secondary nozzle flows were varied independently over a range of nozzle pressure ratios from 1.4 to 3.0 and gas temperatures from 280 to 1100 K. Acoustic data are presented for the conventional mode of coaxial nozzle operation as well as for the inverted velocity profile mode. Comparisons are presented to show the effect of configuration and flow changes on the acoustic characteristics of the nozzles.

  3. Acoustic temperature measurement in a rocket noise field.

    PubMed

    Giraud, Jarom H; Gee, Kent L; Ellsworth, John E

    2010-05-01

    A 1 μm diameter platinum wire resistance thermometer has been used to measure temperature fluctuations generated during a static GEM-60 rocket motor test. Exact and small-signal relationships between acoustic pressure and acoustic temperature are derived in order to compare the temperature probe output with that of a 3.18 mm diameter condenser microphone. After preliminary plane wave tests yielded good agreement between the transducers within the temperature probe's ∼2 kHz bandwidth, comparison between the temperature probe and microphone data during the motor firing show that the ±∼3 K acoustic temperature fluctuations are a significant contributor to the total temperature variations.

  4. Tip-path-plane angle effects on rotor blade-vortex interaction noise levels and directivity

    NASA Technical Reports Server (NTRS)

    Burley, Casey L.; Martin, Ruth M.

    1988-01-01

    Acoustic data of a scale model BO-105 main rotor acquired in a large aeroacoustic wind tunnel are presented to investigate the parametric effects of rotor operating conditions on blade-vortex interaction (BVI) impulsive noise. Contours of a BVI noise metric are employed to quantify the effects of rotor advance ratio and tip-path-plane angle on BVI noise directivity and amplitude. Acoustic time history data are presented to illustrate the variations in impulsive characteristics. The directionality, noise levels and impulsive content of both advancing and retreating side BVI are shown to vary significantly with tip-path-plane angle and advance ratio over the range of low and moderate flight speeds considered.

  5. Noise levels in an urban Asian school environment.

    PubMed

    Chan, Karen M K; Li, Chi Mei; Ma, Estella P M; Yiu, Edwin M L; McPherson, Bradley

    2015-01-01

    Background noise is known to adversely affect speech perception and speech recognition. High levels of background noise in school classrooms may affect student learning, especially for those pupils who are learning in a second language. The current study aimed to determine the noise level and teacher speech-to-noise ratio (SNR) in Hong Kong classrooms. Noise level was measured in 146 occupied classrooms in 37 schools, including kindergartens, primary schools, secondary schools and special schools, in Hong Kong. The mean noise levels in occupied kindergarten, primary school, secondary school and special school classrooms all exceeded recommended maximum noise levels, and noise reduction measures were seldom used in classrooms. The measured SNRs were not optimal and could have adverse implications for student learning and teachers' vocal health. Schools in urban Asian environments are advised to consider noise reduction measures in classrooms to better comply with recommended maximum noise levels for classrooms.

  6. Noise levels in an urban Asian school environment

    PubMed Central

    Chan, Karen M.K.; Li, Chi Mei; Ma, Estella P.M.; Yiu, Edwin M.L.; McPherson, Bradley

    2015-01-01

    Background noise is known to adversely affect speech perception and speech recognition. High levels of background noise in school classrooms may affect student learning, especially for those pupils who are learning in a second language. The current study aimed to determine the noise level and teacher speech-to-noise ratio (SNR) in Hong Kong classrooms. Noise level was measured in 146 occupied classrooms in 37 schools, including kindergartens, primary schools, secondary schools and special schools, in Hong Kong. The mean noise levels in occupied kindergarten, primary school, secondary school and special school classrooms all exceeded recommended maximum noise levels, and noise reduction measures were seldom used in classrooms. The measured SNRs were not optimal and could have adverse implications for student learning and teachers’ vocal health. Schools in urban Asian environments are advised to consider noise reduction measures in classrooms to better comply with recommended maximum noise levels for classrooms. PMID:25599758

  7. Noise suppression by an acoustically treated three-ring inlet on a TF-34 engine

    NASA Technical Reports Server (NTRS)

    Minner, G. L.; Goldman, R. G.; Heidelberg, L. J.

    1976-01-01

    Acoustic performance tests were conducted with a three-ring inlet noise suppressor designed for a TF-34 engine. For all tests the aft noise sources were highly suppressed. The measured inlet suppression was large, reaching levels greater than 30 db at the peak. Comparisons of the data and the performance predictions were in reasonably good agreement. The frequency of peak attenuation was well predicted; the magnitude and spectral shape were reasonably well predicted. Agreement was best when the distribution of sound energy across the inlet was taken into account in the performance predictions. Tests in which the length of treatment was varied showed an orderly progression of attenuation with length; performance predictions for the different lengths also showed an orderly progression with length. At the highest speed of the engine, multiple pure tones were present throughout the spectrum in the source noise signature. These tones were effectively suppressed by the inlet liner, even at low frequencies, although the liner was designed to work best at the blade-passing frequency.

  8. Embedded Acoustic Sensor Array for Engine Fan Noise Source Diagnostic Test: Feasibility of Noise Telemetry via Wireless Smart Sensors

    NASA Technical Reports Server (NTRS)

    Zaman, Afroz; Bauch, Matthew; Raible, Daniel

    2011-01-01

    Aircraft engines have evolved into a highly complex system to meet ever-increasing demands. The evolution of engine technologies has primarily been driven by fuel efficiency, reliability, as well as engine noise concerns. One of the sources of engine noise is pressure fluctuations that are induced on the stator vanes. These local pressure fluctuations, once produced, propagate and coalesce with the pressure waves originating elsewhere on the stator to form a spinning pressure pattern. Depending on the duct geometry, air flow, and frequency of fluctuations, these spinning pressure patterns are self-sustaining and result in noise which eventually radiate to the far-field from engine. To investigate the nature of vane pressure fluctuations and the resulting engine noise, unsteady pressure signatures from an array of embedded acoustic sensors are recorded as a part of vane noise source diagnostics. Output time signatures from these sensors are routed to a control and data processing station adding complexity to the system and cable loss to the measured signal. "Smart" wireless sensors have data processing capability at the sensor locations which further increases the potential of wireless sensors. Smart sensors can process measured data locally and transmit only the important information through wireless communication. The aim of this wireless noise telemetry task was to demonstrate a single acoustic sensor wireless link for unsteady pressure measurement, and thus, establish the feasibility of distributed smart sensors scheme for aircraft engine vane surface unsteady pressure data transmission and characterization.

  9. 49 CFR 325.7 - Allowable noise levels.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 5 2010-10-01 2010-10-01 false Allowable noise levels. 325.7 Section 325.7... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION GENERAL REGULATIONS COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS General Provisions § 325.7 Allowable noise levels. Motor vehicle noise emissions,...

  10. 49 CFR 325.7 - Allowable noise levels.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 5 2014-10-01 2014-10-01 false Allowable noise levels. 325.7 Section 325.7... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION GENERAL REGULATIONS COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS General Provisions § 325.7 Allowable noise levels. Motor vehicle noise emissions,...

  11. 49 CFR 325.7 - Allowable noise levels.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 5 2011-10-01 2011-10-01 false Allowable noise levels. 325.7 Section 325.7... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION GENERAL REGULATIONS COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS General Provisions § 325.7 Allowable noise levels. Motor vehicle noise emissions,...

  12. 49 CFR 325.7 - Allowable noise levels.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 5 2012-10-01 2012-10-01 false Allowable noise levels. 325.7 Section 325.7... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION GENERAL REGULATIONS COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS General Provisions § 325.7 Allowable noise levels. Motor vehicle noise emissions,...

  13. 49 CFR 325.7 - Allowable noise levels.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 5 2013-10-01 2013-10-01 false Allowable noise levels. 325.7 Section 325.7... ADMINISTRATION, DEPARTMENT OF TRANSPORTATION GENERAL REGULATIONS COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS General Provisions § 325.7 Allowable noise levels. Motor vehicle noise emissions,...

  14. Noise levels in primary schools of medium sized city in Greece.

    PubMed

    Sarantopoulos, George; Lykoudis, Spyros; Kassomenos, Pavlos

    2014-06-01

    This study presents and evaluates noise levels recorded at 15 school complexes in order to describe the indoor as well as the outdoor acoustic environment of schools and gain insight on controlling factors. Noise levels at the roadside in front of the school, the schoolyard, and 41 classrooms, both occupied and unoccupied, were simultaneously and continuously recorded through the course of a daily timetable (08:20-13:10). The average speech noise level of teachers was separately measured for 1min periods. Indoor noise levels, in all cases, were much higher than internationally recommended values: LAeq,5min averaged 69.0dB in occupied classrooms, and 47.1dB in unoccupied ones. Average speech-to-noise ratio (SNR) was estimated to be 12.0dB(A) during teaching, whereas both indoor and outdoor noise levels were significantly elevated during break time and outdoor physical-educational activities. Corresponding measurements of indoor and outdoor noise suggest that noise from the outside (road and schoolyard) affects the background noise level in the classrooms, however in varying degrees, depending on the specific layout and road traffic characteristics. Using double glazing diminishes this effect.

  15. Singing whales generate high levels of particle motion: implications for acoustic communication and hearing?

    PubMed

    Mooney, T Aran; Kaplan, Maxwell B; Lammers, Marc O

    2016-11-01

    Acoustic signals are fundamental to animal communication, and cetaceans are often considered bioacoustic specialists. Nearly all studies of their acoustic communication focus on sound pressure measurements, overlooking the particle motion components of their communication signals. Here we characterized the levels of acoustic particle velocity (and pressure) of song produced by humpback whales. We demonstrate that whales generate acoustic fields that include significant particle velocity components that are detectable over relatively long distances sufficient to play a role in acoustic communication. We show that these signals attenuate predictably in a manner similar to pressure and that direct particle velocity measurements can provide bearings to singing whales. Whales could potentially use such information to determine the distance of signalling animals. Additionally, the vibratory nature of particle velocity may stimulate bone conduction, a hearing modality found in other low-frequency specialized mammals, offering a parsimonious mechanism of acoustic energy transduction into the massive ossicles of whale ears. With substantial concerns regarding the effects of increasing anthropogenic ocean noise and major uncertainties surrounding mysticete hearing, these results highlight both an unexplored pathway that may be available for whale acoustic communication and the need to better understand the biological role of acoustic particle motion.

  16. A simplified approach for the calculation of acoustic emission in the case of friction-induced noise and vibration

    NASA Astrophysics Data System (ADS)

    Soobbarayen, K.; Besset, S.; Sinou, J.-. J.

    2015-01-01

    The acoustic response associated with squeal noise radiations is a hard issue due to the need to consider non-linearities of contact and friction, to solve the associated nonlinear dynamic problem and to calculate the noise emissions due to self-excited vibrations. In this work, the focus is on the calculation of the sound pressure in free space generated during squeal events. The calculation of the sound pressure can be performed by the Boundary Element Method (BEM). The inputs of this method are a boundary element model, a field of normal velocity characterized by a unique frequency. However, the field of velocity associated with friction-induced vibrations is composed of several harmonic components. So, the BEM equation has to be solved for each frequency and in most cases, the number of harmonic components is significant. Therefore, the computation time can be prohibitive. The reduction of the number of harmonic component is a key point for the quick estimation of the squeal noise. The proposed approach is based on the detection and the selection of the predominant harmonic components in the mean square velocity. It is applied on two cases of squeal and allows us to consider only few frequencies. In this study, a new method will be proposed in order to quickly well estimate the noise emission in free space. This approach will be based on an approximated acoustic power of brake system which is assumed to be a punctual source, an interpolated directivity and the decrease of the acoustic power levels. This method is applied on two classical cases of squeal with one and two unstable modes. It allows us to well reconstruct the acoustic power levels map. Several error estimators are introduced and show that the reconstructed field is close to the reference calculated with a complete BEM.

  17. Intelligent background noise reduction technology in cable fault locator using the magneto-acoustic synchronous method

    NASA Astrophysics Data System (ADS)

    Mi, JianWei; Huang, JiFa; Fang, XiaoLi; Fan, LiBin

    2017-01-01

    The magneto-acoustic synchronous method has found wide application in accurate positioning of power cable fault due to its advantages of high accuracy and strong ability to reject interference. In the view of principle, the magneto-acoustic synchronous method needs to detect the discharge sound signal and electromagnetic signal emitted from the fault point, but the discharge sound signal is easy to be interfered by the ambient noise around and the magnetic sound synchronization. Therefore, it is challenging to quickly and accurately detect the fault location of cable especially in strong background noise environment. On the other hand, the spectral subtraction is a relatively traditional and effective method in many intelligent background noise reduction technologies, which is characterized by a relatively small computational cost and strong real-time performance. However, its application is limited because the algorithm displays poor performance in low Signal to Noise Ratio (SNR) environment. Aiming at the shortcoming of the spectral subtraction that de-noising effect is weak in low SNR environment, this paper proposes an improved spectral subtraction combining the magnetic sound synchronous principle and analyzing the properties of discharging sound. This method can accurately estimate noise in real time and optimize the performance of the basic spectral subtraction thus solving the problem that the magneto-acoustic synchronous method is unsatisfactory for positioning cable fault in the strong background noise environment.

  18. Critical assessment of thermal/acoustical insulation for pipe and duct noise

    NASA Astrophysics Data System (ADS)

    Hale, Marlund E.

    2005-09-01

    Piping and duct networks are among the major sources and distributors of noise in power plants. This noise is generated primarily by large rotating equipment and devices, primarily valves, with a large pressure drop. Piping and duct noise controls include silencers, thermal/acoustical insulation (lagging), and special treatments (e.g., low noise valve trims and diffusers). The effectiveness of acoustical lagging for pipe and duct noise depends on the type of source, coupling of the piping to sources or support structures, and the frequency spectra radiated. The acoustical performance of pipe lagging systems has been reported by a number of researchers over the past several decades. Today both ASTM and ISO have issued testing standards for the evaluation of pipe lagging systems, and the ISO standard also provides pipe lagging design guidance. Current technology for measuring the TL of lagging, predicting pipe and duct noise, and predicting the IL of lagging is critically assessed. This paper reviews the methods and results of the two standards and compares several laboratory test results with field measurements. Some challenges are presented along with suggestions for improving prediction of piping and ductwork noise abatement within power plants and in the community.

  19. Acoustic and vibration response of a structure with added noise control treatment under various excitations.

    PubMed

    Rhazi, Dilal; Atalla, Noureddine

    2014-02-01

    The evaluation of the acoustic performance of noise control treatments is of great importance in many engineering applications, e.g., aircraft, automotive, and building acoustics applications. Numerical methods such as finite- and boundary elements allow for the study of complex structures with added noise control treatment. However, these methods are computationally expensive when used for complex structures. At an early stage of the acoustic trim design process, many industries look for simple and easy to use tools that provide sufficient physical insight that can help to formulate design criteria. The paper presents a simple and tractable approach for the acoustic design of noise control treatments. It presents and compares two transfer matrix-based methods to investigate the vibroacoustic behavior of noise control treatments. The first is based on a modal approach, while the second is based on wave-number space decomposition. In addition to the classical rain-on-the-roof and diffuse acoustic field excitations, the paper also addresses turbulent boundary layer and point source (monopole) excitations. Various examples are presented and compared to a finite element calculation to validate the methodology and to confirm its relevance along with its limitations.

  20. TU-F-CAMPUS-I-04: Head-Only Asymmetric Gradient System Evaluation: ACR Image Quality and Acoustic Noise

    SciTech Connect

    Weavers, P; Shu, Y; Tao, S; Bernstein, M; Lee, S; Piel, J; Foo, T; Mathieu, J-B

    2015-06-15

    Purpose: A high-performance head-only magnetic resonance imaging gradient system with an acquisition volume of 26 cm employing an asymmetric design for the transverse coils has been developed. It is able to reach a magnitude of 85 mT/m at a slew rate of 700 T/m/s, but operated at 80 mT/m and 500 T/m/s for this test. A challenge resulting from this asymmetric design is that the gradient nonlinearly exhibits both odd- and even-ordered terms, and as the full imaging field of view is often used, the nonlinearity is pronounced. The purpose of this work is to show the system can produce clinically useful images after an on-site gradient nonlinearity calibration and correction, and show that acoustic noise levels fall within non-significant risk (NSR) limits for standard clinical pulse sequences. Methods: The head-only gradient system was inserted into a standard 3T wide-bore scanner without acoustic damping. The ACR phantom was scanned in an 8-channel receive-only head coil and the standard American College of Radiology (ACR) MRI quality control (QC) test was performed. Acoustic noise levels were measured for several standard pulse sequences. Results: Images acquired with the head-only gradient system passed all ACR MR image quality tests; Both even and odd-order gradient distortion correction terms were required for the asymmetric gradients to pass. Acoustic noise measurements were within FDA NSR guidelines of 99 dBA (with assumed 20 dBA hearing protection) A-weighted and 140 dB for peak for all but one sequence. Note the gradient system was installed without any shroud or acoustic batting. We expect final system integration to greatly reduce noise experienced by the patient. Conclusion: A high-performance head-only asymmetric gradient system operating at 80 mT/m and 500 T/m/s conforms to FDA acoustic noise limits in all but one case, and passes all the ACR MR image quality control tests. This work was supported in part by the NIH grant 5R01EB010065.

  1. Neural underpinnings of background acoustic noise in normal aging and mild cognitive impairment.

    PubMed

    Sinanaj, Indrit; Montandon, Marie-Louise; Rodriguez, Cristelle; Herrmann, François; Santini, Francesco; Haller, Sven; Giannakopoulos, Panteleimon

    2015-12-03

    Previous contributions in younger cohorts have revealed that reallocation of cerebral resources, a crucial mechanism for working memory (WM), may be disrupted by parallel demands of background acoustic noise suppression. To date, no study has explored the impact of such disruption on brain activation in elderly individuals with or without subtle cognitive deficits. We performed a functional Magnetic Resonance Imaging (fMRI) study in 23 cases (mean age=75.7 y.o., 16 men) with mild cognitive impairment (MCI) and 16 elderly healthy controls (HC, mean age=70.1 y.o., three men) using a 2-back WM task, under two distinct MRI background acoustic noise conditions (louder vs. lower noise echo-planar imaging). General linear models were used to assess brain activation as a function of group and noise. In both groups, lower background noise is associated with increased activation of the working memory network (WMN). A decrease of the normally observed deactivation of the default mode network (DMN) is found under louder noise in both groups. Unlike HC, MCI cases also show decreased deactivation of the DMN under both louder and lower background noise. Under louder noise, this decrease is observed in anterior parts of the DMN in HC, and in the posterior cingulate cortex in MCI cases. Our results suggest that background acoustic noise has a differential impact on WMN activation in normal aging as a function of the cognitive status. Only louder noise has a disruptive effect on the usually observed DMN deactivation during WM task performance in HC. In contrast, MCI cases show altered DMN reactivity even in the presence of lower noise.

  2. Complete de-Dopplerization and acoustic holography for external noise of a high-speed train.

    PubMed

    Yang, Diange; Wen, Junjie; Miao, Feng; Wang, Ziteng; Gu, Xiaoan; Lian, Xiaomin

    2016-09-01

    Identification and measurement of moving sound sources are the bases for vehicle noise control. Acoustic holography has been applied in successfully identifying the moving sound source since the 1990s. However, due to the high demand for the accuracy of holographic data, currently the maximum velocity achieved by acoustic holography is just above 100 km/h. The objective of this study was to establish a method based on the complete Morse acoustic model to restore the measured signal in high-speed situations, and to propose a far-field acoustic holography method applicable for high-speed moving sound sources. Simulated comparisons of the proposed far-field acoustic holography with complete Morse model, the acoustic holography with simplified Morse model and traditional delay-and-sum beamforming were conducted. Experiments with a high-speed train running at the speed of 278 km/h validated the proposed far-field acoustic holography. This study extended the applications of acoustic holography to high-speed situations and established the basis for quantitative measurements of far-field acoustic holography.

  3. Wind Turbine Generator System Acoustic Noise Test Report for the ARE 442 Wind Turbine

    SciTech Connect

    Huskey, A.; van Dam, J.

    2010-11-01

    This test was conducted on the ARE 442 as part of the U.S. Department of Energy's (DOE's) Independent Testing project. This project was established to help reduce the barriers of wind energy expansion by providing independent testing results for small turbines. In total, five turbines are being tested at the National Wind Technology Center (NWTC) as a part of this project. Acoustic noise testing is one of up to five tests that may be performed on the turbines, including duration, safety and function, power performance, and power quality tests. The acoustic noise test was conducted to the IEC 61400-11 Edition 2.1.

  4. Separation of acoustic modes in the Florida Straits using noise interferometry

    NASA Astrophysics Data System (ADS)

    Sergeev, S. N.; Shurup, A. S.; Godin, O. A.; Vedenev, A. I.; Goncharov, V. V.; Mukhanov, P. Yu.; Zabotin, N. A.; Brown, M. G.

    2017-01-01

    We consider separation of acoustic modes in an experiment carried out in the Florida Straits. The features of the approach are separation of modes using data from single hydrophones, not vertical mode arrays, and a passive scheme of noise interferometry in which the source consists of ocean noise. Processing made it possible to reliably separate the first four modes of the acoustic field. The results allow a conclusion on the possible use of this method for shallow-water monitoring under complex hydrological conditions.

  5. Acoustic Noise Test Report for the SWIFT Wind Turbine in Boulder, CO

    SciTech Connect

    Roadman, J.; Huskey, A.

    2013-04-01

    This report summarizes the results of an acoustic noise test that the National Renewable Energy Laboratory (NREL) conducted on the SWIFT wind turbine. This test was conducted in accordance with the International Electrotechnical Commission's (IEC) standard, Wind Turbine Generator Systems Part 11: Acoustic Noise Measurement Techniques, IEC 61400-11 Ed.2.1, 2006-11. However, because the SWIFT is a small turbine, as defined by IEC, NREL used 10-second averages instead of 60-second averages and utilized binning by wind speed instead of regression analysis.

  6. Acoustic Noise Test Report for the Viryd CS8 Wind Turbine

    SciTech Connect

    Roadman, J.; Huskey, A.

    2013-07-01

    This report summarizes the results of an acoustic noise test that the National Renewable Energy Laboratory (NREL) conducted on the Viryd CS8 wind turbine. This test was conducted in accordance with the International Electrotechnical Commission's (IEC) standard, Wind Turbine Generator Systems Part 11: Acoustic Noise Measurement Techniques, IEC 61400-11 Ed.2.1, 2006-11. However, because the Viryd CS8 is a small turbine, as defined by IEC, NREL used 10-second averages instead of 60-second averages and binning by wind speed instead of regression analysis.

  7. Arousal from sleep by noises from aircraft with and without acoustically treated nacelles

    NASA Technical Reports Server (NTRS)

    Lukas, J. S.; Peeler, D. J.; Dobbs, M. E.

    1973-01-01

    The electroencephalographic and behavioral responses during sleep of four subjects, aged 46 to 58 years, to three types of noises were tested over 14 consecutive nights. The stimuli were two DC-8 jet landing noises (each 30 seconds in duration and coming from DC-8 aircraft with and without acoustical treatment on the engine nacelles) and a 4-second burst of pink noise. Each of the noises was tested at nominal intensities of 61 and 79 dBA. Other physical descriptors of the noises were measured or computed. The results indicate that for an equivalent degree of sleep disruption, noise form the jet aircraft with untreated nacelles must be about 6 dBA less intense than the jet with acoustically treated nacelles. Predictions of the effects of noise on sleep appear, tentatively, to attain the highest accuracy when the physical descriptor of noise intensity includes information about the impulsive characteristics of that noise as well as its long-term spectral content.

  8. Frequency-space prediction filtering for acoustic clutter and random noise attenuation in ultrasound imaging

    NASA Astrophysics Data System (ADS)

    Shin, Junseob; Huang, Lianjie

    2016-04-01

    Frequency-space prediction filtering (FXPF), also known as FX deconvolution, is a technique originally developed for random noise attenuation in seismic imaging. FXPF attempts to reduce random noise in seismic data by modeling only real signals that appear as linear or quasilinear events in the aperture domain. In medical ultrasound imaging, channel radio frequency (RF) signals from the main lobe appear as horizontal events after receive delays are applied while acoustic clutter signals from off-axis scatterers and electronic noise do not. Therefore, FXPF is suitable for preserving only the main-lobe signals and attenuating the unwanted contributions from clutter and random noise in medical ultrasound imaging. We adapt FXPF to ultrasound imaging, and evaluate its performance using simulated data sets from a point target and an anechoic cyst. Our simulation results show that using only 5 iterations of FXPF achieves contrast-to-noise ratio (CNR) improvements of 67 % in a simulated noise-free anechoic cyst and 228 % in a simulated anechoic cyst contaminated with random noise of 15 dB signal-to-noise ratio (SNR). Our findings suggest that ultrasound imaging with FXPF attenuates contributions from both acoustic clutter and random noise and therefore, FXPF has great potential to improve ultrasound image contrast for better visualization of important anatomical structures and detection of diseased conditions.

  9. Towards a Comprehensive Model of Jet Noise Using an Acoustic Analogy and Steady RANS Solutions

    NASA Technical Reports Server (NTRS)

    Miller, Steven A. E.

    2013-01-01

    An acoustic analogy is developed to predict the noise from jet flows. It contains two source models that independently predict the noise from turbulence and shock wave shear layer interactions. The acoustic analogy is based on the Euler equations and separates the sources from propagation. Propagation effects are taken into account by calculating the vector Green's function of the linearized Euler equations. The sources are modeled following the work of Tam and Auriault, Morris and Boluriaan, and Morris and Miller. A statistical model of the two-point cross-correlation of the velocity fluctuations is used to describe the turbulence. The acoustic analogy attempts to take into account the correct scaling of the sources for a wide range of nozzle pressure and temperature ratios. It does not make assumptions regarding fine- or large-scale turbulent noise sources, self- or shear-noise, or convective amplification. The acoustic analogy is partially informed by three-dimensional steady Reynolds-Averaged Navier-Stokes solutions that include the nozzle geometry. The predictions are compared with experiments of jets operating subsonically through supersonically and at unheated and heated temperatures. Predictions generally capture the scaling of both mixing noise and BBSAN for the conditions examined, but some discrepancies remain that are due to the accuracy of the steady RANS turbulence model closure, the equivalent sources, and the use of a simplified vector Green's function solver of the linearized Euler equations.

  10. The acoustic environment of the Florida manatee: Correlation with level of habitat use

    NASA Astrophysics Data System (ADS)

    Miksis-Olds, Jennifer L.; Miller, James H.; Tyack, Peter L.

    2004-05-01

    The Florida manatee is regularly exposed to high volumes of vessel traffic and other human-related noise pollutants because of their coastal distribution. Quantifying specific aspects of the manatees' acoustic environment will allow for a better understanding of how these animals are responding to both natural and human induced changes in their environment. Acoustic recordings and transmission loss measurements were made in two critical manatee habitats: seagrass beds and dredged basins. Twenty-four sampling sites were chosen based on the frequency of manatee presence in specific areas from 2000-2003. Recordings were composed of both ambient noise levels and transient noise sources. The Monterey-Miami Parabolic Equation Model (MMPE) was used to relate environmental parameters to transmission loss, and model outputs were verified by field tests at all sites. Preliminary results indicate that high-use grassbeds have higher levels of transmission loss compared to low-use sites. Additionally, high-use grassbeds have lower ambient noise in the early morning and later afternoon hours compared to low-use grassbeds. The application of noise measurements and model results can now be used to predict received levels, signal-to-noise ratios, and reliable detection of biologically relevant signals in manatee habitats and in the many different environments that marine mammals live.

  11. The acoustic environment of the Florida manatee: Correlation with level of habitat use

    NASA Astrophysics Data System (ADS)

    Miksis-Olds, Jennifer L.; Miller, James H.; Tyack, Peter L.

    2001-05-01

    The Florida manatee is regularly exposed to high volumes of vessel traffic and other human-related noise pollutants because of their coastal distribution. Quantifying specific aspects of the manatees' acoustic environment will allow for a better understanding of how these animals are responding to both natural and human induced changes in their environment. Acoustic recordings and transmission loss measurements were made in two critical manatee habitats: seagrass beds and dredged basins. Twenty-four sampling sites were chosen based on the frequency of manatee presence in specific areas from 2000-2003. Recordings were composed of both ambient noise levels and transient noise sources. The Monterey-Miami Parabolic Equation Model (MMPE) was used to relate environmental parameters to transmission loss, and model outputs were verified by field tests at all sites. Preliminary results indicate that high-use grassbeds have higher levels of transmission loss compared to low-use sites. Additionally, high-use grassbeds have lower ambient noise in the early morning and later afternoon hours compared to low-use grassbeds. The application of noise measurements and model results can now be used to predict received levels, signal-to-noise ratios, and reliable detection of biologically relevant signals in manatee habitats and in the many different environments that marine mammals live.

  12. Acoustic-optic spectrometer. 1: Noise contributions and system consideration

    NASA Technical Reports Server (NTRS)

    Chin, G.

    1984-01-01

    An acousto-optic spectrometer (AOS) used as an IF spectrometer to a heterodyne receiver is modeled as a total power multi-channel integrating receiver. Systematic noise contributions common to all total power, time integrating receivers, as well as noise terms unique to the use of optical elements and photo-detectors in an AOS are identified and discussed. In addition, degradation of signal-to-noise ratio of an unbalanced Dicke receiver compared to a balanced Dicke receiver is found to be due to gain calibration processing and is not an instrumental effect.

  13. Single stage, low noise, advanced technology fan. Volume 5: Fan acoustics. Section 1: Results and analysis

    NASA Technical Reports Server (NTRS)

    Jutras, R. R.

    1976-01-01

    The acoustic tests and data analysis for a 0.508-scale fan vehicle of a 111,300 newton (25,000 pound) thrust, full-size engine, which would have application on an advanced transport aircraft, is described. The single-stage advanced technology fan was designed to a pressure ratio of 1.8 at a tip speed of 503 m/sec (1,650 ft/sec) to achieve the desired pressure ratio in a single-stage fan with low radius ratio (0.38), and to maintain adequate stall margin. The fan has 44 tip-shrouded rotor blades and 90 outlet guide vanes. The two basic approaches taken in the acoustic design were: (1) minimization of noise at the source, and (2) suppression of the generated noise in the inlet and bypass exhaust duct. Suppression of the generated noise was accomplished in the inlet through use of the hybrid concept (wall acoustic treatment plus airflow acceleration suppression) and in the exhaust duct with extensive acoustic treatment including a splitter. The goal of the design was attainment of twenty effective perceived noise decibels (20 EPNdB) below current Federal Air Regulation noise standards for a full-scale fan at the takeoff, cutback, and approach conditions. The suppression goal of FAR 36-20 was not reached, but improvements in the technology of both front and aft fan-noise suppression were realized. The suppressed fan noise was shown to be consistent with the proposed federal regulation on aircraft noise.

  14. High Frequency Acoustic Channel Characterization for Propagation and Ambient Noise

    DTIC Science & Technology

    2006-09-30

    with Michael Porter and the ONR High Frequency Initiative and the ONR PLUSNet program. REFERENCES M. B. Porter and H. P. Bucker, “Gaussian...Harrison and Michael Porter , “A passive fathometer for determining bottom depth and imaging seabed layering using ambient noise”, J. Acoust. Soc. Am., 120

  15. Deep-Water Ambient Noise Profiling; Marine Sediment Acoustics; and Doppler Geo-Acoustic Spectroscopy

    DTIC Science & Technology

    2012-09-30

    explosive volcanic eruptions ,” J. Comp. Acoust., 9 (3), 1215-1225 (2001) [keynote address, published, refereed]. 24. N. G. Lehtinen, S. Adam, G...B02209, doi:10, 1-12 (2009) [published, refereed] 9. M. J. Buckingham, “On the transient solutions of three acoustic wave equations: van Wijngaarden’s

  16. Deep-Water Ambient Noise Profiling; Marine Sediment Acoustics; and Doppler Geo-Acoustic Spectroscopy

    DTIC Science & Technology

    2013-09-30

    explosive volcanic eruptions ,” J. Comp. Acoust., 9 (3), 1215-1225 (2001) [keynote address, published, refereed]. 25. N. G. Lehtinen, S. Adam, G. Gratta...doi:10, 1-12 (2009) [published, refereed] 10. M. J. Buckingham, “On the transient solutions of three acoustic wave equations: van Wijngaarden’s

  17. Comments on "Effects of Noise on Speech Production: Acoustic and Perceptual Analyses" [J. Acoust. Soc. Am. 84, 917-928 (1988)].

    PubMed

    Fitch, H

    1989-11-01

    The effect of background noise on speech production is an important issue, both from the practical standpoint of developing speech recognition algorithms and from the theoretical standpoint of understanding how speech is tuned to the environment in which it is spoken. Summers et al. [J. Acoust. Soc. Am. 84, 917-928 (1988]) address this issue by experimentally manipulating the level of noise delivered through headphones to two talkers and making several kinds of acoustic measurements on the resulting speech. They indicate that they have replicated effects on amplitude, duration, and pitch and have found effects on spectral tilt and first-formant frequency (F1). The authors regard these acoustic changes as effects in themselves rather than as consequences of a change in vocal effort, and thus treat equally the change in spectral tilt and the change in F1. In fact, the change in spectral tilt is a well-documented and understood consequence of the change in the glottal waveform, which is known to occur with increased effort. The situation with F1 is less clear and is made difficult by measurement problems. The bias in linear predictive coding (LPC) techniques related to two of the other changes-fundamental frequency and spectral tilt-is discussed.

  18. Noise levels and their effects on Shuttle crewmembers' performance: Operational concerns

    NASA Technical Reports Server (NTRS)

    Koros, Anton S.; Adam, Susan C.; Wheelwright, Charles D.

    1993-01-01

    When excessive, noise can result in sleep interference, fatigue, interference with verbal communication, and hearing damage. Shuttle crewmembers are exposed to noise throughout their mission. The contribution of noise to decrements in crew performance over these extended exposure durations was the focus of this study. On the STS-40/SLS-1, mission noise levels were evaluated through the use of a sound level meter and a crew questionnaire. Crewmembers noted that sleep, concentration, and relaxation were negatively impacted by high noise levels. Speech Interference Levels (SIL's), calculated from the sound level measurements, suggested that crewmembers were required to raise their voice in order to be heard. No difficulty detecting caution and warning alarms was noted. The higher than desirable noise levels in Spacelab were attributed to flight specific payloads for which acoustic waivers were granted. It is recommended that current noise levels be reduced in Spacelab and the Orbiter Middeck especially as longer missions are planned for the buildup of Space Station Freedom. Levels of NC 50 are recommended in areas where speech communication is required and NC 40 in sleep areas. These levels are in accordance with the NASA Man-Systems Integration Standards. Measurements proposed for subsequent orbiter missions are discussed.

  19. Relationships between non-acoustic factors and subjective reactions to floor impact noise in apartment buildings.

    PubMed

    Park, Sang Hee; Lee, Pyoung Jik; Yang, Kwan Seop; Kim, Kyoung Woo

    2016-03-01

    The aim of this study was to provide an understanding of how residents in apartment buildings perceive and react to impact sounds coming from the upstairs neighbours' dwellings. Based on existing theoretical and empirical studies on environmental noise, a conceptual model was developed to explain relationships among noise annoyance and non-acoustic factors. The model was then tested using structural equation modelling with survey data from residents living in apartment buildings (N = 487). The findings showed that the conceptual model was consistent with other models developed for environmental noises. The results indicated that annoyance induced by floor impact noise was associated with perceived disturbance, coping, and self-reported health complaints. Noise sensitivity had a direct impact on perceived disturbance and an indirect impact on annoyance, and moderating variables affected the non-acoustic factors. Exposure to footstep noises increased the impact size of noise sensitivity to disturbance. Predictability, marital status, and house ownership were found to influence the relationship between attitudes towards authorities and coping. In addition, a negative attitude towards neighbours (i.e., the noise source) moderated the positive relationship between annoyance and coping.

  20. Noise Levels and Annoyance in Open Plan Educational Facilities

    ERIC Educational Resources Information Center

    Walsh, David P.

    1975-01-01

    This paper investigates the special considerations in defining an acoustical environment acceptable for educational purposes. Reviews various approaches for anticipating the degree of dissatisfaction or annoyance in school spaces, including statistical distributions of class noise, and deals with some design recommendations. (Author/MLF)

  1. Structural sensing of interior sound for active control of noise in structural-acoustic cavities.

    PubMed

    Bagha, Ashok K; Modak, S V

    2015-07-01

    This paper proposes a method for structural sensing of acoustic potential energy for active control of noise in a structural-acoustic cavity. The sensing strategy aims at global control and works with a fewer number of sensors. It is based on the established concept of radiation modes and hence does not add too many states to the order of the system. Acoustic potential energy is sensed using a combination of a Kalman filter and a frequency weighting filter with the structural response measurements as the inputs. The use of Kalman filter also makes the system robust against measurement noise. The formulation of the strategy is presented using finite element models of the system including that of sensors and actuators so that it can be easily applied to practical systems. The sensing strategy is numerically evaluated in the framework of Linear Quadratic Gaussian based feedback control of interior noise in a rectangular box cavity with a flexible plate with single and multiple pairs of piezoelectric sensor-actuator patches when broadband disturbances act on the plate. The performance is compared with an "acoustic filter" that models the complete transfer function from the structure to the acoustic domain. The sensing performance is also compared with a direct estimation strategy.

  2. Effects of sound level fluctuations on annoyance caused by aircraft-flyover noise

    NASA Technical Reports Server (NTRS)

    Mccurdy, D. A.

    1979-01-01

    A laboratory experiment was conducted to determine the effects of variations in the rate and magnitude of sound level fluctuations on the annoyance caused by aircraft-flyover noise. The effects of tonal content, noise duration, and sound pressure level on annoyance were also studied. An aircraft-noise synthesis system was used to synthesize 32 aircraft-flyover noise stimuli representing the factorial combinations of 2 tone conditions, 2 noise durations, 2 sound pressure levels, 2 level fluctuation rates, and 2 level fluctuation magnitudes. Thirty-two test subjects made annoyance judgements on a total of 64 stimuli in a subjective listening test facility simulating an outdoor acoustic environment. Variations in the rate and magnitude of level fluctuations were found to have little, if any, effect on annoyance. Tonal content, noise duration, sound pressure level, and the interaction of tonal content with sound pressure level were found to affect the judged annoyance significantly. The addition of tone corrections and/or duration corrections significantly improved the annoyance prediction ability of noise rating scales.

  3. Wind Turbine Acoustic Investigation: Infrasound and Low-Frequency Noise--A Case Study

    ERIC Educational Resources Information Center

    Ambrose, Stephen E.; Rand, Robert W.; Krogh, Carmen M. E.

    2012-01-01

    Wind turbines produce sound that is capable of disturbing local residents and is reported to cause annoyance, sleep disturbance, and other health-related impacts. An acoustical study was conducted to investigate the presence of infrasonic and low-frequency noise emissions from wind turbines located in Falmouth, Massachusetts, USA. During the…

  4. Relation of acoustic noise parameters during remagnetization with the mechanical and magnetic properties of ferromagnetic materials

    SciTech Connect

    Glukhov, N.A.; Kolmogorov, V.N.

    1988-10-01

    An analysis is made of the principal publications concerned with the acoustic noise of remagnetization (ANR) and by means of this, with the inclusion of well-known energy relations for domain theory, the association of internal stresses and grain size with the starting field and ANR is explained. The conclusions are supported with experimental data.

  5. Information-bearing acoustic change outperforms duration in predicting intelligibility of full-spectrum and noise-vocoded sentences.

    PubMed

    Stilp, Christian E

    2014-03-01

    Recent research has demonstrated a strong relationship between information-bearing acoustic changes in the speech signal and speech intelligibility. The availability of information-bearing acoustic changes reliably predicts intelligibility of full-spectrum [Stilp and Kluender (2010). Proc. Natl. Acad. Sci. U.S.A. 107(27), 12387-12392] and noise-vocoded sentences amid noise interruption [Stilp et al. (2013). J. Acoust. Soc. Am. 133(2), EL136-EL141]. However, other research reports that proportion of signal duration preserved also predicts intelligibility of noise-interrupted speech. These factors have only ever been investigated independently, obscuring whether one better explains speech perception. The present experiments manipulated both factors to answer this question. A broad range of sentence durations (160-480 ms) containing high or low information-bearing acoustic changes were replaced by speech-shaped noise in noise-vocoded (Experiment 1) and full-spectrum sentences (Experiment 2). Sentence intelligibility worsened with increasing noise replacement, but in both experiments, information-bearing acoustic change was a statistically superior predictor of performance. Perception relied more heavily on information-bearing acoustic changes in poorer listening conditions (in spectrally degraded sentences and amid increasing noise replacement). Highly linear relationships between measures of information and performance suggest that exploiting information-bearing acoustic change is a shared principle underlying perception of acoustically rich and degraded speech. Results demonstrate the explanatory power of information-theoretic approaches for speech perception.

  6. Amplification of interaural level differences improves sound localization in acoustic simulations of bimodal hearing.

    PubMed

    Francart, Tom; Van den Bogaert, Tim; Moonen, Marc; Wouters, Jan

    2009-12-01

    Users of a cochlear implant and contralateral hearing aid are sensitive to interaural level differences (ILDs). However, when using their clinical devices, most of these subjects cannot use ILD cues for localization in the horizontal plane. This is partly due to a lack of high-frequency residual hearing in the acoustically stimulated ear. Using acoustic simulations of a cochlear implant and hearing loss, it is shown that localization performance can be improved by up to 14 degrees rms error relative to 48 degrees rms error for broadband noise by artificially introducing ILD cues in the low frequencies. The algorithm that was used for ILD introduction is described.

  7. Aero-acoustic performance comparison of core engine noise suppressors on NASA quiet engine C

    NASA Technical Reports Server (NTRS)

    Bloomer, H. E.; Schaefer, J. W.

    1977-01-01

    The relative aero-acoustic effectiveness of two core engine suppressors, a contractor-designed suppressor delivered with the Quiet Engine, and a NASA-designed suppressor was evaluated. The NASA suppressor was tested with and without a splitter making a total of three configurations being reported in addition to the baseline hardwall case. The aerodynamic results are presented in terms of tailpipe pressure loss, corrected net thrust, and corrected specific fuel consumption as functions of engine power setting. The acoustic results are divided into duct and far-field acoustic data. The NASA-designed core suppressor did the better job of suppressing aft end noise, but the splitter associated with it caused a significant engine performance penality. The NASA core suppressor without the spltter suppressed most of the core noise without any engine performance penalty.

  8. Aero-acoustic performance comparison of core engine noise suppressors on NASA quiet engine 'C'

    NASA Technical Reports Server (NTRS)

    Bloomer, H. E.; Schaefer, J. W.

    1977-01-01

    The purpose of the experimental program reported herein was to evaluate and compare the relative aero-acoustic effectiveness of two core engine suppressors, a contractor-designed suppressor delivered with the Quiet Engine, and a NASA-designed suppressor, designed and built subsequently. The NASA suppressor was tested with and without a splitter making a total of three configurations being reported in addition to the baseline hardwall case. The aerodynamic results are presented in terms of tailpipe pressure loss, corrected net thrust, and corrected specific fuel consumption as functions of engine power setting. The acoustic results are divided into duct and far-field acoustic data. The NASA-designed core suppressor did the better job of suppressing aft end noise, but the splitter associated with it caused a significant engine performance penalty. The NASA core suppressor without the splitter suppressed most of the core noise without any engine performance penalty.

  9. Response of space shuttle insulation panels to acoustic noise pressure

    NASA Technical Reports Server (NTRS)

    Vaicaitis, R.

    1976-01-01

    The response of reusable space shuttle insulation panels to random acoustic pressure fields are studied. The basic analytical approach in formulating the governing equations of motion uses a Rayleigh-Ritz technique. The input pressure field is modeled as a stationary Gaussian random process for which the cross-spectral density function is known empirically from experimental measurements. The response calculations are performed in both frequency and time domain.

  10. Flap Side-Edge Noise: Acoustic Analysis of Sen's Model

    NASA Technical Reports Server (NTRS)

    Hardin, Jay C.; Martin, James E.

    1996-01-01

    The two-dimensional flap side-edge flow model developed by Sen is analyzed to reveal the noise production potential of the proposed mechanism. The model assumes that a vortex will form at the equilibrium position off the side edge of the flap. The vortex is then perturbed away from the equilibrium position by incoming turbulence causing it to oscillate and thus radiate sound. The noise field is calculated three-dimensionally by taking the flap to have a finite chord. Spectra and directivity of the farfield sound are presented. In addition, the effect of retarded time differences is evaluated. The parameters in the model are related to typical aircraft parameters and noise reduction possibilities are proposed.

  11. Single-image noise level estimation for blind denoising.

    PubMed

    Liu, Xinhao; Tanaka, Masayuki; Okutomi, Masatoshi

    2013-12-01

    Noise level is an important parameter to many image processing applications. For example, the performance of an image denoising algorithm can be much degraded due to the poor noise level estimation. Most existing denoising algorithms simply assume the noise level is known that largely prevents them from practical use. Moreover, even with the given true noise level, these denoising algorithms still cannot achieve the best performance, especially for scenes with rich texture. In this paper, we propose a patch-based noise level estimation algorithm and suggest that the noise level parameter should be tuned according to the scene complexity. Our approach includes the process of selecting low-rank patches without high frequency components from a single noisy image. The selection is based on the gradients of the patches and their statistics. Then, the noise level is estimated from the selected patches using principal component analysis. Because the true noise level does not always provide the best performance for nonblind denoising algorithms, we further tune the noise level parameter for nonblind denoising. Experiments demonstrate that both the accuracy and stability are superior to the state of the art noise level estimation algorithm for various scenes and noise levels.

  12. The Prediction of Jet Noise Ground Effects Using an Acoustic Analogy and a Tailored Green's Function

    NASA Technical Reports Server (NTRS)

    Miller, Steven A. E.

    2013-01-01

    An assessment of an acoustic analogy for the mixing noise component of jet noise in the presence of an infinite surface is presented. The reflection of jet noise by the ground changes the distribution of acoustic energy and is characterized by constructive and destructive interference patterns. The equivalent sources are modeled based on the two-point cross- correlation of the turbulent velocity fluctuations and a steady Reynolds-Averaged Navier-Stokes (RANS) solution. Propagation effects, due to reflection by the surface and refaction by the jet shear layer, are taken into account by calculating the vector Green's function of the linearized Euler equations (LEE). The vector Green's function of the LEE is written in relation to Lilley's equation; that is, approximated with matched asymptotic solutions and the Green's function of the convective Helmholtz equation. The Green's function of the convective Helmholtz equation for an infinite flat plane with impedance is the Weyl-van der Pol equation. Predictions are compared with an unheated Mach 0.95 jet produced by a nozzle with an exit diameter of 0.3302 meters. Microphones are placed at various heights and distances from the nozzle exit in the peak jet noise direction above an acoustically hard and an asphalt surface. The predictions are shown to accurately capture jet noise ground effects that are characterized by constructive and destructive interference patterns in the mid- and far-field and capture overall trends in the near-field.

  13. A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation

    PubMed Central

    Hu, Yi

    2010-01-01

    Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions. PMID:21117763

  14. A simulation study of harmonics regeneration in noise reduction for electric and acoustic stimulation.

    PubMed

    Hu, Yi

    2010-05-01

    Recent research results show that combined electric and acoustic stimulation (EAS) significantly improves speech recognition in noise, and it is generally established that access to the improved F0 representation of target speech, along with the glimpse cues, provide the EAS benefits. Under noisy listening conditions, noise signals degrade these important cues by introducing undesired temporal-frequency components and corrupting harmonics structure. In this study, the potential of combining noise reduction and harmonics regeneration techniques was investigated to further improve speech intelligibility in noise by providing improved beneficial cues for EAS. Three hypotheses were tested: (1) noise reduction methods can improve speech intelligibility in noise for EAS; (2) harmonics regeneration after noise reduction can further improve speech intelligibility in noise for EAS; and (3) harmonics sideband constraints in frequency domain (or equivalently, amplitude modulation in temporal domain), even deterministic ones, can provide additional benefits. Test results demonstrate that combining noise reduction and harmonics regeneration can significantly improve speech recognition in noise for EAS, and it is also beneficial to preserve the harmonics sidebands under adverse listening conditions. This finding warrants further work into the development of algorithms that regenerate harmonics and the related sidebands for EAS processing under noisy conditions.

  15. Acoustic and streaming velocity components in a resonant waveguide at high acoustic levels.

    PubMed

    Daru, Virginie; Reyt, Ida; Bailliet, Hélène; Weisman, Catherine; Baltean-Carlès, Diana

    2017-01-01

    Rayleigh streaming is a steady flow generated by the interaction between an acoustic wave and a solid wall, generally assumed to be second order in a Mach number expansion. Acoustic streaming is well known in the case of a stationary plane wave at low amplitude: it has a half-wavelength spatial periodicity and the maximum axial streaming velocity is a quadratic function of the acoustic velocity amplitude at antinode. For higher acoustic levels, additional streaming cells have been observed. Results of laser Doppler velocimetry measurements are here compared to direct numerical simulations. The evolution of axial and radial velocity components for both acoustic and streaming velocities is studied from low to high acoustic amplitudes. Two streaming flow regimes are pointed out, the axial streaming dependency on acoustics going from quadratic to linear. The evolution of streaming flow is different for outer cells and for inner cells. Also, the hypothesis of radial streaming velocity being of second order in a Mach number expansion, is not valid at high amplitudes. The change of regime occurs when the radial streaming velocity amplitude becomes larger than the radial acoustic velocity amplitude, high levels being therefore characterized by nonlinear interaction of the different velocity components.

  16. The Influences of Lamination Angles on the Interior Noise Levels of an Aircraft

    NASA Technical Reports Server (NTRS)

    Fernholz, Christian M.; Robinson, Jay H.

    1996-01-01

    The feasibility of reducing the interior noise levels of an aircraft passenger cabin through optimization of the composite lay up of the fuselage is investigated. MSC/NASTRAN, a commercially available finite element code, is used to perform the dynamic analysis and subsequent optimization of the fuselage. The numerical calculation of sensitivity of acoustic pressure to lamination angle is verified using a simple thin, cylindrical shell with point force excitations as noise sources. The thin shell used represents a geometry similar to the fuselage and analytic solutions are available for the cylindrical thin shell equations of motion. Optimization of lamination angle for the reduction of interior noise is performed using a finite element model of an actual aircraft fuselage. The aircraft modeled for this study is the Beech Starship. Point forces simulate the structure borne noise produced by the engines and are applied to the fuselage at the wing mounting locations. These forces are the noise source for the optimization problem. The acoustic pressure response is reduced at a number of points in the fuselage and over a number of frequencies. The objective function is minimized with the constraint that it be larger than the maximum sound pressure level at the response points in the passenger cabin for all excitation frequencies in the range of interest. Results from the study of the fuselage model indicate that a reduction in interior noise levels is possible over a finite frequency range through optimal configuration of the lamination angles in the fuselage. Noise reductions of roughly 4 dB were attained. For frequencies outside the optimization range, the acoustic pressure response may increase after optimization. The effects of changing lamination angle on the overall structural integrity of the airframe are not considered in this study.

  17. Acoustic noise improves motor learning in spontaneously hypertensive rats, a rat model of attention deficit hyperactivity disorder.

    PubMed

    Söderlund, Göran B W; Eckernäs, Daniel; Holmblad, Olof; Bergquist, Filip

    2015-03-01

    The spontaneously hypertensive (SH) rat model of ADHD displays impaired motor learning. We used this characteristic to study if the recently described acoustic noise benefit in learning in children with ADHD is also observed in the SH rat model. SH rats and a Wistar control strain were trained in skilled reach and rotarod running under either ambient noise or in 75 dBA white noise. In other animals the effect of methylphenidate (MPH) on motor learning was assessed with the same paradigms. To determine if acoustic noise influenced spontaneous motor activity, the effect of acoustic noise was also determined in the open field activity paradigm. We confirm impaired motor learning in the SH rat compared to Wistar SCA controls. Acoustic noise restored motor learning in SH rats learning the Montoya reach test and the rotarod test, but had no influence on learning in Wistar rats. Noise had no effect on open field activity in SH rats, but increased corner time in Wistar. MPH completely restored rotarod learning and performance but did not improve skilled reach in the SH rat. It is suggested that the acoustic noise benefit previously reported in children with ADHD is shared by the SH rat model of ADHD, and the effect is in the same range as that of stimulant treatment. Acoustic noise may be useful as a non-pharmacological alternative to stimulant medication in the treatment of ADHD.

  18. Characterizing noise in nonhuman vocalizations: Acoustic analysis and human perception of barks by coyotes and dogs

    NASA Astrophysics Data System (ADS)

    Riede, Tobias; Mitchell, Brian R.; Tokuda, Isao; Owren, Michael J.

    2005-07-01

    Measuring noise as a component of mammalian vocalizations is of interest because of its potential relevance to the communicative function. However, methods for characterizing and quantifying noise are less well established than methods applicable to harmonically structured aspects of signals. Using barks of coyotes and domestic dogs, we compared six acoustic measures and studied how they are related to human perception of noisiness. Measures of harmonic-to-noise-ratio (HNR), percent voicing, and shimmer were found to be the best predictors of perceptual rating by human listeners. Both acoustics and perception indicated that noisiness was similar across coyote and dog barks, but within each species there was significant variation among the individual vocalizers. The advantages and disadvantages of the various measures are discussed.

  19. Hunting at the highway: traffic noise reduces foraging efficiency in acoustic predators.

    PubMed

    Siemers, Björn M; Schaub, Andrea

    2011-06-07

    Noise pollution from human traffic networks and industrial activity impacts vast areas of our planet. While anthropogenic noise effects on animal communication are well documented, we have very limited understanding of noise impact on more complex ecosystem processes, such as predator-prey interactions, albeit urgently needed to devise mitigation measures. Here, we show that traffic noise decreases the foraging efficiency of an acoustic predator, the greater mouse-eared bat (Myotis myotis). These bats feed on large, ground-running arthropods that they find by listening to their faint rustling sounds. We measured the bats' foraging performance on a continuous scale of acoustically simulated highway distances in a behavioural experiment, designed to rule out confounding factors such as general noise avoidance. Successful foraging bouts decreased and search time drastically increased with proximity to the highway. At 7.5 m to the road, search time was increased by a factor of five. From this increase, we predict a 25-fold decrease in surveyed ground area and thus in foraging efficiency for a wild bat. As most of the bats' prey are predators themselves, the noise impact on the bats' foraging performance will have complex effects on the food web and ultimately on the ecosystem stability. Similar scenarios apply to other ecologically important and highly protected acoustic predators, e.g. owls. Our study provides the empirical basis for quantitative predictions of anthropogenic noise impacts on ecosystem processes. It highlights that an understanding of the effects of noise emissions and other forms of 'sensory pollution' are crucially important for the assessment of environmental impact of human activities.

  20. Hunting at the highway: traffic noise reduces foraging efficiency in acoustic predators

    PubMed Central

    Siemers, Björn M.; Schaub, Andrea

    2011-01-01

    Noise pollution from human traffic networks and industrial activity impacts vast areas of our planet. While anthropogenic noise effects on animal communication are well documented, we have very limited understanding of noise impact on more complex ecosystem processes, such as predator–prey interactions, albeit urgently needed to devise mitigation measures. Here, we show that traffic noise decreases the foraging efficiency of an acoustic predator, the greater mouse-eared bat (Myotis myotis). These bats feed on large, ground-running arthropods that they find by listening to their faint rustling sounds. We measured the bats' foraging performance on a continuous scale of acoustically simulated highway distances in a behavioural experiment, designed to rule out confounding factors such as general noise avoidance. Successful foraging bouts decreased and search time drastically increased with proximity to the highway. At 7.5 m to the road, search time was increased by a factor of five. From this increase, we predict a 25-fold decrease in surveyed ground area and thus in foraging efficiency for a wild bat. As most of the bats' prey are predators themselves, the noise impact on the bats' foraging performance will have complex effects on the food web and ultimately on the ecosystem stability. Similar scenarios apply to other ecologically important and highly protected acoustic predators, e.g. owls. Our study provides the empirical basis for quantitative predictions of anthropogenic noise impacts on ecosystem processes. It highlights that an understanding of the effects of noise emissions and other forms of ‘sensory pollution’ are crucially important for the assessment of environmental impact of human activities. PMID:21084347

  1. An exploratory survey of noise levels associated with a 100kW wind turbine

    NASA Technical Reports Server (NTRS)

    Balombin, J. R.

    1980-01-01

    Noise measurements of a 125-foot diameter, 100 kW wind turbine are presented. The data include measurements as functions of distance from the turbine and directivity angle and cover a frequency range from 1 Hz to several kHz. Potential community impact is discussed in terms of A-weighted noise levels relative to background levels, and the intrasonic spectral content. Finally, the change in the sound power spectrum associated with a change in the rotor speed in described. The acoustic impact of this size wind turbine is judged to be minimal.

  2. Noise reduction of a composite cylinder subjected to random acoustic excitation

    NASA Technical Reports Server (NTRS)

    Grosveld, Ferdinand W.; Beyer, T.

    1989-01-01

    Interior and exterior noise measurements were conducted on a stiffened composite floor-equipped cylinder, with and without an interior trim installed. Noise reduction was obtained for the case of random acoustic excitation in a diffuse field; the frequency range of interest was 100-800-Hz one-third octave bands. The measured data were compared with noise reduction predictions from the Propeller Aircraft Interior Noise (PAIN) program and from a statistical energy analysis. Structural model parameters were not predicted well by the PAIN program for the given input parameters; this resulted in incorrect noise reduction predictions for the lower one-third octave bands where the power flow into the interior of the cylinder was predicted on a mode-per-mode basis.

  3. An acoustic range for the measurement of the noise signature of aircraft during flyby operations

    NASA Technical Reports Server (NTRS)

    Hilton, D. A.; Henderson, H. R.

    1978-01-01

    The remotely operated multiple array acoustic range (ROMAAR), which has been developed to give direct measurement and display of aircraft noise in several measurement units during takeoff, landing, and flyby operations, is described. The ROMAAR, which provides information on the ground noise signature of aircraft, represents a unique combination of state-of-the-art digital and analog noise-recording methods, computer-controlled digital communication methods, radar tracking facilities, quick-look weather (profile) capabilities, and sophisticated data handling routines and facilities. The ROMAAR, which is operated by NASA, allows direct data feedback to the NASA Aircraft Noise Prediction Office. As many as 38 simultaneous noise measurements can be made for each aircraft overflight.

  4. Structure borne noise analysis using Helmholtz equation least squares based forced vibro acoustic components

    NASA Astrophysics Data System (ADS)

    Natarajan, Logesh Kumar

    This dissertation presents a structure-borne noise analysis technology that is focused on providing a cost-effective noise reduction strategy. Structure-borne sound is generated or transmitted through structural vibration; however, only a small portion of the vibration can effectively produce sound and radiate it to the far-field. Therefore, cost-effective noise reduction is reliant on identifying and suppressing the critical vibration components that are directly responsible for an undesired sound. However, current technologies cannot successfully identify these critical vibration components from the point of view of direct contribution to sound radiation and hence cannot guarantee the best cost-effective noise reduction. The technology developed here provides a strategy towards identifying the critical vibration components and methodically suppressing them to achieve a cost-effective noise reduction. The core of this technology is Helmholtz equation least squares (HELS) based nearfield acoustic holography method. In this study, the HELS formulations derived in spherical co-ordinates using spherical wave expansion functions utilize the input data of acoustic pressures measured in the nearfield of a vibrating object to reconstruct the vibro-acoustic responses on the source surface and acoustic quantities in the far field. Using these formulations, three steps were taken to achieve the goal. First, hybrid regularization techniques were developed to improve the reconstruction accuracy of normal surface velocity of the original HELS method. Second, correlations between the surface vibro-acoustic responses and acoustic radiation were factorized using singular value decomposition to obtain orthogonal basis known here as the forced vibro-acoustic components (F-VACs). The F-VACs enables one to identify the critical vibration components for sound radiation in a similar manner that modal decomposition identifies the critical natural modes in a structural vibration. Finally

  5. Acoustic theory of axisymmetric multisectioned ducts. [reduction of turbofan engine noise

    NASA Technical Reports Server (NTRS)

    Zorumski, W. E.

    1974-01-01

    Equations are developed for the acoustic field in a duct system which is made up of a number of connected circular and annular ducts. These equations are suitable for finding the acoustic field inside of and radiated from an aircraft turbofan engine. Acoustic modes are used as generalized coordinates in order to develop a set of matrix equations for the acoustic field. Equations for these modes are given for circular and annular ducts with uniform flow. Modal source equations are derived for point acoustic sources. General equations for mode transmission and reflection are developed and detailed equations are derived for ducts with multiple sections of acoustic treatment and for ducts with circumferential splitter rings. The general theory is applied to the special case of a uniform area circular duct with multisection liners and it is shown that the mode reflection effects are proportional to differences of the acoustic admittances of adjacent liners. A numerical example is given which shows that multisection liners may provide greater noise suppression than uniform liners.

  6. Acoustic Context Alters Vowel Categorization in Perception of Noise-Vocoded Speech.

    PubMed

    Stilp, Christian E

    2017-03-09

    Normal-hearing listeners' speech perception is widely influenced by spectral contrast effects (SCEs), where perception of a given sound is biased away from stable spectral properties of preceding sounds. Despite this influence, it is not clear how these contrast effects affect speech perception for cochlear implant (CI) users whose spectral resolution is notoriously poor. This knowledge is important for understanding how CIs might better encode key spectral properties of the listening environment. Here, SCEs were measured in normal-hearing listeners using noise-vocoded speech to simulate poor spectral resolution. Listeners heard a noise-vocoded sentence where low-F1 (100-400 Hz) or high-F1 (550-850 Hz) frequency regions were amplified to encourage "eh" (/ɛ/) or "ih" (/ɪ/) responses to the following target vowel, respectively. This was done by filtering with +20 dB (experiment 1a) or +5 dB gain (experiment 1b) or filtering using 100 % of the difference between spectral envelopes of /ɛ/ and /ɪ/ endpoint vowels (experiment 2a) or only 25 % of this difference (experiment 2b). SCEs influenced identification of noise-vocoded vowels in each experiment at every level of spectral resolution. In every case but one, SCE magnitudes exceeded those reported for full-spectrum speech, particularly when spectral peaks in the preceding sentence were large (+20 dB gain, 100 % of the spectral envelope difference). Even when spectral resolution was insufficient for accurate vowel recognition, SCEs were still evident. Results are suggestive of SCEs influencing CI users' speech perception as well, encouraging further investigation of CI users' sensitivity to acoustic context.

  7. Aero acoustic analysis and community noise. HSCT climb to cruise noise assessment

    NASA Technical Reports Server (NTRS)

    Mortlock, Alan K.

    1992-01-01

    The widely accepted industry High Speed Civil Transport (HSCT) design goal for exterior noise is to achieve Federal Aviation Regulation (FAR) Part 36 Stage 3 noise limits currently required for new subsonic aircraft. The three phases of the concern are as follows: (1) airport noise abatement at communities close to the airport, (2) climb power opening-up procedures, and (3) the climb to cruise phase affecting communities far from the airport.

  8. Acoustic communication in two freshwater gobies: ambient noise and short-range propagation in shallow streams.

    PubMed

    Lugli, M; Fine, M L

    2003-07-01

    Noise is an important theoretical constraint on the evolution of signal form and sensory performance. In order to determine environmental constraints on the communication of two freshwater gobies Padogobius martensii and Gobius nigricans, numerous noise spectra were measured from quiet areas and ones adjacent to waterfalls and rapids in two shallow stony streams. Propagation of goby sounds and waterfall noise was also measured. A quiet window around 100 Hz is present in many noise spectra from noisy locations. The window lies between two noise sources, a low-frequency one attributed to turbulence, and a high-frequency one (200-500 Hz) attributed to bubble noise from water breaking the surface. Ambient noise from a waterfall (frequencies below 1 kHz) attenuates as much as 30 dB between 1 and 2 m, after which values are variable without further attenuation (i.e., buried in the noise floor). Similarly, courtship sounds of P. martensii attenuate as much as 30 dB between 5 and 50 cm. Since gobies are known to court in noisy as well as quiet locations in these streams, their acoustic communication system (sounds and auditory system) must be able to cope with short-range propagation dictated by shallow depths and ambient noise in noisy locations.

  9. Maintaining acoustic communication at a cocktail party: heterospecific masking noise improves signal detection through frequency separation

    PubMed Central

    Siegert, M. E.; Römer, H.; Hartbauer, M.

    2014-01-01

    SUMMARY We examined acoustic masking in a chirping katydid species of the Mecopoda elongata complex due to interference with a sympatric Mecopoda species where males produce continuous trills at high amplitudes. Frequency spectra of both calling songs range from 1 to 80 kHz; the chirper species has more energy in a narrow frequency band at 2 kHz and above 40 kHz. Behaviourally, chirper males successfully phase-locked their chirps to playbacks of conspecific chirps under masking conditions at signal-to-noise ratios (SNRs) of −8 dB. After the 2 kHz band in the chirp had been equalised to the level in the masking trill, the breakdown of phase-locked synchrony occurred at a SNR of +7 dB. The remarkable receiver performance is partially mirrored in the selective response of a first-order auditory interneuron (TN1) to conspecific chirps under these masking conditions. However, the selective response is only maintained for a stimulus including the 2 kHz component, although this frequency band has no influence on the unmasked TN1 response. Remarkably, the addition of masking noise at 65 dB sound pressure level (SPL) to threshold response levels of TN1 for pure tones of 2 kHz enhanced the sensitivity of the response by 10 dB. Thus, the spectral dissimilarity between masker and signal at a rather low frequency appears to be of crucial importance for the ability of the chirping species to communicate under strong masking by the trilling species. We discuss the possible properties underlying the cellular/synaptic mechanisms of the ‘novelty detector’. PMID:24307713

  10. Ocean acoustic remote sensing using ambient noise: results from the Florida Straits

    NASA Astrophysics Data System (ADS)

    Brown, M. G.; Godin, O. A.; Zang, X.; Ball, J. S.; Zabotin, N. A.; Zabotina, L. Y.; Williams, N. J.

    2016-07-01

    Noise interferometry is the process by which approximations to acoustic Green's functions, which describe sound propagation between two locations, are estimated by cross-correlating time series of ambient noise measured at those locations. Noise-interferometry-based approximations to Green's functions can be used as the basis for a variety of inversion algorithms, thereby providing a purely passive alternative to active-source ocean acoustic remote sensing. In this paper we give an overview of results from noise interferometry experiments conducted in the Florida Straits at 100 m depth in December 2012, and at 600 m depth in September/October 2013. Under good conditions for noise interferometry, estimates of cross-correlation functions are shown to allow one to perform advanced phase-coherent signal processing techniques to perform waveform inversions, estimate currents by exploiting non-reciprocity, perform time-reversal/back-propagation calculations and investigate modal dispersion using time-warping techniques. Conditions which are favourable for noise interferometry are identified and discussed.

  11. Efficiency of a Noise Barrier on the Ground with AN Acoustically Soft Cylindrical Edge

    NASA Astrophysics Data System (ADS)

    Okubo, T.; Fujiwara, K.

    1998-10-01

    It is well known that an absorptive obstacle installed on the edge of a noise barrier improves sound shielding efficiency without increasing the height of the barrier. This paper examines the sound shielding efficiency of a noise barrier with an acoustically “soft” cylindrical edge. “Soft” indicates that the sound pressure at the surface is zero; however, it is difficult to produce a soft surface using traditional materials. The authors previously reported that the “Waterwheel cylinder,” which consists of acoustic tubes arranged radially, approximates a soft surface cylinder. In the present study, a noise barrier with a Waterwheel cylinder installed on the edge of the barrier is investigated. Results of numerical simulations indicated that the Waterwheel cylinder improves the sound shielding efficiency of a noise barrier. The improvement is strongly frequency dependent; it exceeds 10 dB in a certain frequency range of an octave, but the Waterwheel decreases the noise shielding efficiency in another frequency range. The frequency characteristics of the waterwheel's effects are related to its self cross-sectional shape. The Waterwheel improves the efficiency much better in the effective frequency range of an octave as compared with an absorbing cylinder. All numerical calculations were carried out assuming an unrealistic two-dimensional sound field, but results of scale model experiments indicate that the calculations predict very accurately the efficiency of noise barriers in a three-dimensional sound field.

  12. Ambient noise levels and detection threshold in Norway.

    PubMed

    Demuth, Andrea; Ottemöller, Lars; Keers, Henk

    2016-01-01

    Ambient seismic noise is caused by a number of sources in specific frequency bands. The quantification of ambient noise makes it possible to evaluate station and network performance. We evaluate noise levels in Norway from the 2013 data set of the Norwegian National Seismic Network as well as two temporary deployments. Apart from the station performance, we studied the geographical and temporal variations, and developed a local noise model for Norway. The microseism peaks related to the ocean are significant in Norway. We, therefore, investigated the relationship between oceanic weather conditions and noise levels. We find a correlation of low-frequency noise (0.125-0.25 Hz) with wave heights up to 900 km offshore. High (2-10 Hz) and intermediate (0.5-5 Hz) frequency noise correlates only up to 450 km offshore with wave heights. From a geographic perspective, stations in southern Norway show lower noise levels for low frequencies due to a larger distance to the dominant noise sources in the North Atlantic. Finally, we studied the influence of high-frequency noise levels on earthquake detectability and found that a noise level increase of 10 dB decreases the detectability by 0.5 magnitude units. This method provides a practical way to consider noise variations in detection maps.

  13. Noise level and MPEG-2 encoder statistics

    NASA Astrophysics Data System (ADS)

    Lee, Jungwoo

    1997-01-01

    Most software in the movie and broadcasting industries are still in analog film or tape format, which typically contains random noise that originated from film, CCD camera, and tape recording. The performance of the MPEG-2 encoder may be significantly degraded by the noise. It is also affected by the scene type that includes spatial and temporal activity. The statistical property of noise originating from camera and tape player is analyzed and the models for the two types of noise are developed. The relationship between the noise, the scene type, and encoder statistics of a number of MPEG-2 parameters such as motion vector magnitude, prediction error, and quant scale are discussed. This analysis is intended to be a tool for designing robust MPEG encoding algorithms such as preprocessing and rate control.

  14. Deep ocean sound speed characteristics passively derived from the ambient acoustic noise field

    NASA Astrophysics Data System (ADS)

    Evers, L. G.; Wapenaar, K.; Heaney, K. D.; Snellen, M.

    2017-02-01

    The propagation of acoustic waves in the ocean strongly depends on the temperature. Low frequency acoustic waves can penetrate the ocean down to depths where few in-situ measurements are available. It is therefore attractive to obtain a measure of the deep ocean temperature from acoustic waves. The latter is especially true if the ambient acoustic noise field can be used instead of deterministic transient signals. In this study the acoustic velocity, and hence the temperature, is derived in an interferometric approach from hydrophone array recordings. The arrays were separated by over 125 km, near Ascension Island in the Atlantic Ocean, at a depth of 850m. Furthermore, the dispersive characteristics of the deep ocean sound channel are resolved based on the retrieved lag times for different modes. In addition, it is shown how the resolution of the interferometric approach can be increased by cross correlating array beams rather than recordings from single-sensor pairs. The observed acoustic lag times between the arrays corresponds well to modeled values, based on full-wave modeling through best-known oceanic models.

  15. The Relationship between Vessel Traffic and Noise Levels Received by Killer Whales (Orcinus orca).

    PubMed

    Houghton, Juliana; Holt, Marla M; Giles, Deborah A; Hanson, M Bradley; Emmons, Candice K; Hogan, Jeffrey T; Branch, Trevor A; VanBlaricom, Glenn R

    2015-01-01

    Whale watching has become increasingly popular as an ecotourism activity around the globe and is beneficial for environmental education and local economies. Southern Resident killer whales (Orcinus orca) comprise an endangered population that is frequently observed by a large whale watching fleet in the inland waters of Washington state and British Columbia. One of the factors identified as a risk to recovery for the population is the effect of vessels and associated noise. An examination of the effects of vessels and associated noise on whale behavior utilized novel equipment to address limitations of previous studies. Digital acoustic recording tags (DTAGs) measured the noise levels the tagged whales received while laser positioning systems allowed collection of geo-referenced data for tagged whales and all vessels within 1000 m of the tagged whale. The objective of the current study was to compare vessel data and DTAG recordings to relate vessel traffic to the ambient noise received by tagged whales. Two analyses were conducted, one including all recording intervals, and one that excluded intervals when only the research vessel was present. For all data, significant predictors of noise levels were length (inverse relationship), number of propellers, and vessel speed, but only 15% of the variation in noise was explained by this model. When research-vessel-only intervals were excluded, vessel speed was the only significant predictor of noise levels, and explained 42% of the variation. Simple linear regressions (ignoring covariates) found that average vessel speed and number of propellers were the only significant correlates with noise levels. We conclude that vessel speed is the most important predictor of noise levels received by whales in this study. Thus, measures that reduce vessel speed in the vicinity of killer whales would reduce noise exposure in this population.

  16. The Relationship between Vessel Traffic and Noise Levels Received by Killer Whales (Orcinus orca)

    PubMed Central

    Houghton, Juliana; Holt, Marla M.; Giles, Deborah A.; Hanson, M. Bradley; Emmons, Candice K.; Hogan, Jeffrey T.; Branch, Trevor A.; VanBlaricom, Glenn R.

    2015-01-01

    Whale watching has become increasingly popular as an ecotourism activity around the globe and is beneficial for environmental education and local economies. Southern Resident killer whales (Orcinus orca) comprise an endangered population that is frequently observed by a large whale watching fleet in the inland waters of Washington state and British Columbia. One of the factors identified as a risk to recovery for the population is the effect of vessels and associated noise. An examination of the effects of vessels and associated noise on whale behavior utilized novel equipment to address limitations of previous studies. Digital acoustic recording tags (DTAGs) measured the noise levels the tagged whales received while laser positioning systems allowed collection of geo-referenced data for tagged whales and all vessels within 1000 m of the tagged whale. The objective of the current study was to compare vessel data and DTAG recordings to relate vessel traffic to the ambient noise received by tagged whales. Two analyses were conducted, one including all recording intervals, and one that excluded intervals when only the research vessel was present. For all data, significant predictors of noise levels were length (inverse relationship), number of propellers, and vessel speed, but only 15% of the variation in noise was explained by this model. When research-vessel-only intervals were excluded, vessel speed was the only significant predictor of noise levels, and explained 42% of the variation. Simple linear regressions (ignoring covariates) found that average vessel speed and number of propellers were the only significant correlates with noise levels. We conclude that vessel speed is the most important predictor of noise levels received by whales in this study. Thus, measures that reduce vessel speed in the vicinity of killer whales would reduce noise exposure in this population. PMID:26629916

  17. The relationship between vessel traffic and noise levels received by killer whales (Orcinus orca)

    USGS Publications Warehouse

    Houghton, Juliana; Holt, Marla M.; Giles, Deborah A.; Hanson, M. Bradley; Emmons, Candice K.; Hogan, Jeffrey T.; Branch, Trevor A.; Vanblaricom, Glenn R.

    2015-01-01

    Whale watching has become increasingly popular as an ecotourism activity around the globe and is beneficial for environmental education and local economies. Southern Resident killer whales (Orcinus orca) comprise an endangered population that is frequently observed by a large whale watching fleet in the inland waters of Washington state and British Columbia. One of the factors identified as a risk to recovery for the population is the effect of vessels and associated noise. An examination of the effects of vessels and associated noise on whale behavior utilized novel equipment to address limitations of previous studies. Digital acoustic recording tags (DTAGs) measured the noise levels the tagged whales received while laser positioning systems allowed collection of geo-referenced data for tagged whales and all vessels within 1000 m of the tagged whale. The objective of the current study was to compare vessel data and DTAG recordings to relate vessel traffic to the ambient noise received by tagged whales. Two analyses were conducted, one including all recording intervals, and one that excluded intervals when only the research vessel was present. For all data, significant predictors of noise levels were length (inverse relationship), number of propellers, and vessel speed, but only 15% of the variation in noise was explained by this model. When research-vessel-only intervals were excluded, vessel speed was the only significant predictor of noise levels, and explained 42% of the variation. Simple linear regressions (ignoring covariates) found that average vessel speed and number of propellers were the only significant correlates with noise levels. We conclude that vessel speed is the most important predictor of noise levels received by whales in this study. Thus, measures that reduce vessel speed in the vicinity of killer whales would reduce noise exposure in this population.

  18. Acoustic Analog to Quantum Mechanical Level-Splitting

    NASA Astrophysics Data System (ADS)

    Hilbert, Shawn

    2010-03-01

    One difficulty in teaching quantum mechanics is the lack of classroom demonstrations. To sidestep this issue, analogies can provide an enlightening alternative. Acoustics governance by the same time-independent wave equation as quantum mechanics supports it use in such analogies. This presentation examines one such analogy for an infinite potential well with a delta potential perturbation. The physical acoustic system consists of continuous sounds waves traveling in a pair of tubes which are separated by a variable diaphragm. The level-splitting nature of the quantum system can be mimicked in the acoustic system.

  19. Current levels of noise in an urban environment.

    PubMed

    Fisher, G H

    1973-12-01

    In 1961, the International Organization for Standardization prescribed upper tolerance limits for noise generated out-of-doors in residential districts. Between 1963 and 1970, vehicular traffic in the UK increased in volume by approximately 40%. This paper describes studies made throughout 1971 in which both peak and ambient noise-levels prevailing inside and outside buildings were measured. These levels were found greatly in excess of those regarded as tolerable ten years previously. Two methods for reducing noise-levels were considered. First, a barrier designed with the primary intention of reflecting rather than absorbing noise; secondly, a relatively simple form of double-glazing fitted to existing window frames. The barrier succeeded in reducing peak noise-levels but failed to influence ambients. The double-glazing attenuated both peak and ambient noise-levels significantly. Attention is drawn to the possibility of noise generated within buildings themselves becoming a source of discomfort for occupants and of annoyance to those outside. Noise-levels rising beyond 100 dB(A) were measured during evening business in the bar of a local hotel. A summary of data referring to noise-levels in the outdoor environment reveals that the upper tolerance limits prescribed by I S O are now being exceeded by 20 dB(A), or more, throughout 18 hours of the day. The findings are discussed in relation to the inevitable limits soon to be reached in adaptation of the human hearing mechanisms to increasing environment noise.

  20. Noise in small portable motocompressors. Experiments on limited-cost acoustic treatments to obtain progressive improvements

    NASA Astrophysics Data System (ADS)

    Collober, J.; Corlay, B.

    1984-04-01

    Design modifications are proposed in order to help motocompressor manufacturers to reduce the noise level to 85 dBA. Work on 8kW groups shows that the noise sources are, in order of importance, the internal combustion motor exhaust, the air inlet, the cooling air circuit and the oil pan. The effects of an inlet air filter, an exhaust noise attenuator and a cover on the motocompressor are discussed. A noise reduction of 10dBA is obtained.

  1. The Acoustic Analogy: A Powerful Tool in Aeroacoustics with Emphasis on Jet Noise Prediction

    NASA Technical Reports Server (NTRS)

    Farassat, F.; Doty, Michael J.; Hunter, Craig A.

    2004-01-01

    The acoustic analogy introduced by Lighthill to study jet noise is now over 50 years old. In the present paper, Lighthill s Acoustic Analogy is revisited together with a brief evaluation of the state-of-the-art of the subject and an exploration of the possibility of further improvements in jet noise prediction from analytical methods, computational fluid dynamics (CFD) predictions, and measurement techniques. Experimental Particle Image Velocimetry (PIV) data is used both to evaluate turbulent statistics from Reynolds-averaged Navier-Stokes (RANS) CFD and to propose correlation models for the Lighthill stress tensor. The NASA Langley Jet3D code is used to study the effect of these models on jet noise prediction. From the analytical investigation, a retarded time correction is shown that improves, by approximately 8 dB, the over-prediction of aft-arc jet noise by Jet3D. In experimental investigation, the PIV data agree well with the CFD mean flow predictions, with room for improvement in Reynolds stress predictions. Initial modifications, suggested by the PIV data, to the form of the Jet3D correlation model showed no noticeable improvements in jet noise prediction.

  2. Influence of gradient acoustic noise on fMRI response in the human visual cortex.

    PubMed

    Zhang, Nanyin; Zhu, Xiao-Hong; Chen, Wei

    2005-08-01

    A paired-stimuli paradigm combined with fMRI was utilized to study the effect of gradient acoustic noise on fMRI response in the human primary visual cortex (V1) in terms of the auditory-visual cross-modal neural interaction. The gradient noise generated during the fMRI acquisition was used as the primary stimulus, and a single flashing light was used as the secondary stimulus. An interstimulus interval (ISI) separated the two. Six tasks were designed with different ISIs ranging from 50 to 700 ms. Both BOLD signal intensity and the number of activated pixels in V1 were analyzed and examined, and they showed a significant reduction when the gradient noise preceded the flashing light by approximately 300 ms. These results indicate that the gradient acoustic noise generated during fMRI acquisitions does interfere with neural behavior and the BOLD signal in the human visual cortex. This interference is modulated by the delay between the gradient noise and visual stimulation, and it can be studied quantitatively when the stimulation paradigm is designed appropriately. This study provides evidence of the auditory-visual interaction during fMRI studies, and the results should have an impact on fMRI applications.

  3. Nonlinear acoustic propagation of launch vehicle and military jet aircraft noise

    NASA Astrophysics Data System (ADS)

    Gee, Kent L.

    2010-10-01

    The noise from launch vehicles and high-performance military jet aircraft has been shown to travel nonlinearly as a result of an amplitude-dependent speed of sound. Because acoustic pressure compressions travel faster than rarefactions, the waveform steepens and shocks form. This process results in a very different (and readily audible) noise signature and spectrum than predicted by linear models. On-going efforts to characterize the nonlinearity using statistical and spectral measures are described with examples from recent static tests of solid rocket boosters and the F-22 Raptor.

  4. Aircraft interior noise models - Sidewall trim, stiffened structures, and cabin acoustics with floor partition

    NASA Technical Reports Server (NTRS)

    Pope, L. D.; Wilby, E. G.; Willis, C. M.; Mayes, W. H.

    1983-01-01

    As part of the continuing development of an aircraft interior noise prediction model, in which a discrete modal representation and power flow analysis are used, theoretical results are considered for inclusion of sidewall trim, stiffened structures, and cabin acoustics with floor partition. For validation purposes, predictions of the noise reductions for three test articles (a bare ring-stringer stiffened cylinder, an unstiffened cylinder with floor and insulation, and a ring-stringer stiffened cylinder with floor and sidewall trim) are compared with measurements.

  5. Two stage low noise advanced technology fan. 1: Aerodynamic, structural, and acoustic design

    NASA Technical Reports Server (NTRS)

    Messenger, H. E.; Ruschak, J. T.; Sofrin, T. G.

    1974-01-01

    A two-stage fan was designed to reduce noise 20 db below current requirements. The first-stage rotor has a design tip speed of 365.8 m/sec and a hub/tip ratio of 0.4. The fan was designed to deliver a pressure ratio of 1.9 with an adiabatic efficiency of 85.3 percent at a specific inlet corrected flow of 209.2kg/sec/sq m. Noise reduction devices include acoustically treated casing walls, a flowpath exit acoustic splitter, a translating centerbody sonic inlet device, widely spaced blade rows, and the proper ratio of blades and vanes. Multiple-circular-arc rotor airfoils, resettable stators, split outer casings, and capability to go to close blade-row spacing are also included.

  6. Computational Aero-acoustics As a Tool For Turbo-machinery Noise Reduction

    NASA Technical Reports Server (NTRS)

    Dyson, Rodger W.

    2003-01-01

    This talk will provide an overview of the field of computational aero-acoustics and its use in fan noise prediction. After a brief history of computational fluid dynamics, some of the recent developments in computational aero-acoustics will be explored. Computational issues concerning sound wave production, propagation, and reflection in practical turbo-machinery applications will be discussed including: (a) High order/High Resolution Numerical Techniques. (b) High Resolution Boundary Conditions. [c] MIMD Parallel Computing. [d] Form of Governing Equations Useful for Simulations. In addition, the basic design of our Broadband Analysis Stator Simulator (BASS) code and its application to a 2 D rotor wake-stator interaction will be shown. An example of the noise produced by the wakes from a rotor impinging upon a stator cascade will be shown.

  7. Approaches to Adaptive Active Acoustic Noise Control at a Point Using Feedforward Techniques.

    NASA Astrophysics Data System (ADS)

    Zulch, Peter A.

    Active acoustic noise control systems have been of interest since their birth in the 1930's. The principle is to superimpose on an unwanted noise wave shape its inverse with the intention of destructive interference. This work presents two approaches to this idea. The first approach uses a direct design method to develop a controller using an auto-regressive moving-average (ARMA) model that will be used to condition the primary noise to produce the required anti-noise for cancellation. The development of this approach has shown that the stability of the controller relies heavily on a non-minimum phase model of the secondary noise path. For this reason, a second approach, using a controller consisting of two parts was developed. The first part of the controller is designed to cancel broadband noise and the second part is an adaptive controller designed to cancel periodic noise. A simple technique for identifying the parameters of the broadband controller is developed. An ARMA model is used, and it is shown that its stability is improved by prefiltering the test signal with a minimum-phase inverse of the secondary noise channel. The periodic controller uses an estimate of the fundamental frequency to cancel the first few harmonics of periodic noise. A computationally efficient adaptive technique based on least squares is developed for updating the harmonic controller gains at each time step. Experimental results are included for the broadband controller, the harmonic controller, and the combination of the two algorithms. The advantages of using both techniques in conjunction are shown using test cases involving both broadband noise and periodic noise.

  8. Non-linear duct acoustics and its application to fan noise

    NASA Technical Reports Server (NTRS)

    Vaidya, P. G.

    1977-01-01

    Quite often the scalar Helmholtz equation is assumed to be the fundamental equation of duct acoustics and various relations are derived from it. An investigation is, therefore, conducted regarding the underlying assumptions leading to the Helmholtz equation. It is found that serious errors, even well below 186 dB, are possible if the assumption of linearity were to be made. In duct acoustics these errors are highest near the cutoff points and in the case of ducts with transonic flow. It is pointed out that serious errors could arise if a nonlinear problem is analyzed by linear methods. At times, an entire phenomenon remains unpredictable by linear methods. Attention is given to the characteristics of nonlinear systems, the phenomenon of multiple pure tones in the case of noise from the aircraft engine fans, the limitations of the conventional acoustics equation, duct shape and nonlinearity, and the numerical simulation of a fan with 8 blades.

  9. Circuit for echo and noise suppression of acoustic signals transmitted through a drill string

    DOEpatents

    Drumheller, D.S.; Scott, D.D.

    1993-12-28

    An electronic circuit for digitally processing analog electrical signals produced by at least one acoustic transducer is presented. In a preferred embodiment of the present invention, a novel digital time delay circuit is utilized which employs an array of First-in-First-out (FiFo) microchips. Also, a bandpass filter is used at the input to this circuit for isolating drill string noise and eliminating high frequency output. 20 figures.

  10. Noise-adaptive nonlinear diffusion filtering of MR images with spatially varying noise levels.

    PubMed

    Samsonov, Alexei A; Johnson, Chris R

    2004-10-01

    Anisotropic diffusion filtering is widely used for MR image enhancement. However, the anisotropic filter is nonoptimal for MR images with spatially varying noise levels, such as images reconstructed from sensitivity-encoded data and intensity inhomogeneity-corrected images. In this work, a new method for filtering MR images with spatially varying noise levels is presented. In the new method, a priori information regarding the image noise level spatial distribution is utilized for the local adjustment of the anisotropic diffusion filter. Our new method was validated and compared with the standard filter on simulated and real MRI data. The noise-adaptive method was demonstrated to outperform the standard anisotropic diffusion filter in both image error reduction and image signal-to-noise ratio (SNR) improvement. The method was also applied to inhomogeneity-corrected and sensitivity encoding (SENSE) images. The new filter was shown to improve segmentation of MR brain images with spatially varying noise levels.

  11. Noise levels, noise annoyance, and hearing-related problems in a dental college.

    PubMed

    Ahmed, Hafiz Omer; Ali, Wesal Jasim

    2016-04-20

    Through a cross-sectional survey and integrated sound level meter, this research examined noise exposure and auditory- and nonauditory-related problems experienced by students of a dentistry college located in the United Arab Emirates (UAE). A structured interview questionnaire was used to examine hearing-related problems, noise annoyance, and awareness of 114 students toward noise. The results showed that maximum noise levels were between 65 and 79 dB(A) with peak levels (high and low frequencies) ranging between 89 and 93 dB(A). Around 80% of the students experienced a certain degree of noise annoyance; 54% reported one of the hearing-related problems; and about 10% claimed to have hearing loss to a certain extent. It is recommended that sound-absorbent materials be used during the construction of dental clinics and laboratories to reduce the noise levels.

  12. Theoretical vibro-acoustic modeling of acoustic noise transmission through aircraft windows

    NASA Astrophysics Data System (ADS)

    Aloufi, Badr; Behdinan, Kamran; Zu, Jean

    2016-06-01

    In this paper, a fully vibro-acoustic model for sound transmission across a multi-pane aircraft window is developed. The proposed model is efficiently applied for a set of window models to perform extensive theoretical parametric studies. The studied window configurations generally simulate the passenger window designs of modern aircraft classes which have an exterior multi-Plexiglas pane, an interior single acrylic glass pane and a dimmable glass ("smart" glass), all separated by thin air cavities. The sound transmission loss (STL) characteristics of three different models, triple-, quadruple- and quintuple-paned windows identical in size and surface density, are analyzed for improving the acoustic insulation performances. Typical results describing the influence of several system parameters, such as the thicknesses, number and spacing of the window panes, on the transmission loss are then investigated. In addition, a comparison study is carried out to evaluate the acoustic reduction capability of each window model. The STL results show that the higher frequencies sound transmission loss performance can be improved by increasing the number of window panels, however, the low frequency performance is decreased, particularly at the mass-spring resonances.

  13. Development of a Transient Acoustic Boundary Element Method to Predict the Noise Signature of Swimming Fish

    NASA Astrophysics Data System (ADS)

    Wagenhoffer, Nathan; Moored, Keith; Jaworski, Justin

    2015-11-01

    Animals have evolved flexible wings and fins to efficiently and quietly propel themselves through the air and water. The design of quiet and efficient bio-inspired propulsive concepts requires a rapid, unified computational framework that integrates three essential features: the fluid mechanics, the elastic structural response, and the noise generation. This study focuses on the development, validation, and demonstration of a transient, two-dimensional acoustic boundary element solver accelerated by a fast multipole algorithm. The resulting acoustic solver is used to characterize the acoustic signature produced by a vortex street advecting over a NACA 0012 airfoil, which is representative of vortex-body interactions that occur in schools of swimming fish. Both 2S and 2P canonical vortex streets generated by fish are investigated over the range of Strouhal number 0 . 2 < St < 0 . 4 , and the acoustic signature of the airfoil is quantified. This study provides the first estimate of the noise signature of a school of swimming fish. Lehigh University CORE Grant.

  14. Active vibration and noise control of vibro-acoustic system by using PID controller

    NASA Astrophysics Data System (ADS)

    Li, Yunlong; Wang, Xiaojun; Huang, Ren; Qiu, Zhiping

    2015-07-01

    Active control simulation of the acoustic and vibration response of a vibro-acoustic cavity of an airplane based on a PID controller is presented. A full numerical vibro-acoustic model is developed by using an Eulerian model, which is a coupled model based on the finite element formulation. The reduced order model, which is used to design the closed-loop control system, is obtained by the combination of modal expansion and variable substitution. Some physical experiments are made to validate and update the full-order and the reduced-order numerical models. Optimization of the actuator placement is employed in order to get an effective closed-loop control system. For the controller design, an iterative method is used to determine the optimal parameters of the PID controller. The process is illustrated by the design of an active noise and vibration control system for a cavity structure. The numerical and experimental results show that a PID-based active control system can effectively suppress the noise inside the cavity using a sound pressure signal as the controller input. It is also possible to control the noise by suppressing the vibration of the structure using the structural displacement signal as the controller input. For an airplane cavity structure, considering the issue of space-saving, the latter is more suitable.

  15. Wind Turbine Generator System Acoustic Noise Test Report for the Gaia Wind 11-kW Wind Turbine

    SciTech Connect

    Huskey, A.

    2011-11-01

    This report details the acoustic noise test conducted on the Gaia-Wind 11-kW wind turbine at the National Wind Technology Center. The test turbine is a two- bladed, downwind wind turbine with a rated power of 11 kW. The test turbine was tested in accordance with the International Electrotechnical Commission standard, IEC 61400-11 Ed 2.1 2006-11 Wind Turbine Generator Systems -- Part 11 Acoustic Noise Measurement Techniques.

  16. Plumbing noise: Pressure levels and perception in a luxury condominium

    NASA Astrophysics Data System (ADS)

    Watry, Derek

    2005-09-01

    A consulting project has recently been completed that addressed a number of noise concerns in a 9-unit, 20-year-old luxury condominium building in the San Francisco Bay Area. Among other tasks, the noise levels of four bathroom plumbing functions (flushing, showering, bath filling, bath draining) were measured in adjoining units and an inventory of noise concerns was collected. This paper reports the measured noise levels (nearly a 20-dBA range for every function!) and looks at the corresponding resident assessments not always clearly correlated with sound-pressure level.

  17. Passive acoustic detection and localization of whales: effects of shipping noise in Saguenay-St. Lawrence Marine Park.

    PubMed

    Simard, Yvan; Roy, Nathalie; Gervaise, Cédric

    2008-06-01

    The performance of large-aperture hydrophone arrays to detect and localize blue and fin whales' 15-85 Hz signature vocalizations under ocean noise conditions was assessed through simulations from a normal mode propagation model combined to noise statistics from 15 960 h of recordings in Saguenay-St. Lawrence Marine Park. The probability density functions of 2482 summer noise level estimates in the call bands were used to attach a probability of detection/masking to the simulated call levels as a function of whale depth and range for typical environmental conditions. Results indicate that call detection was modulated by the calling depth relative to the sound channel axis and by modal constructive and destructive interferences with range. Masking of loud infrasounds could reach 40% at 30 km for a receiver at the optimal depth. The 30 dB weaker blue whale D-call were subject to severe masking. Mapping the percentages of detection and localization allowed assessing the performance of a six-hydrophone array under mean- and low-noise conditions. This approach is helpful for optimizing hydrophone configuration in implementing passive acoustic monitoring arrays and building their detection function for whale density assessment, as an alternative to or in combination with the traditional undersampling visual methods.

  18. Classification image weights and internal noise level estimation

    NASA Technical Reports Server (NTRS)

    Ahumada, Albert J Jr

    2002-01-01

    For the linear discrimination of two stimuli in white Gaussian noise in the presence of internal noise, a method is described for estimating linear classification weights from the sum of noise images segregated by stimulus and response. The recommended method for combining the two response images for the same stimulus is to difference the average images. Weights are derived for combining images over stimuli and observers. Methods for estimating the level of internal noise are described with emphasis on the case of repeated presentations of the same noise sample. Simple tests for particular hypotheses about the weights are shown based on observer agreement with a noiseless version of the hypothesis.

  19. Isolating the auditory system from acoustic noise during functional magnetic resonance imaging: Examination of noise conduction through the ear canal, head, and bodya)

    PubMed Central

    Ravicz, Michael E.; Melcher, Jennifer R.

    2007-01-01

    Approaches were examined for reducing acoustic noise levels heard by subjects during functional magnetic resonance imaging (fMRI), a technique for localizing brain activation in humans. Specifically, it was examined whether a device for isolating the head and ear canal from sound (a “helmet”) could add to the isolation provided by conventional hearing protection devices (i.e., earmuffs and earplugs). Both subjective attenuation (the difference in hearing threshold with versus without isolation devices in place) and objective attenuation (difference in ear-canal sound pressure) were measured. In the frequency range of the most intense fMRI noise (1–1.4 kHz), a helmet, earmuffs, and earplugs used together attenuated perceived sound by 55–63 dB, whereas the attenuation provided by the conventional devices alone was substantially less: 30–37 dB for earmuffs, 25–28 dB for earplugs, and 39–41 dB for earmuffs and earplugs used together. The data enabled the clarification of the relative importance of ear canal, head, and body conduction routes to the cochlea under different conditions: At low frequencies (≤500 Hz), the ear canal was the dominant route of sound conduction to the cochlea for all of the device combinations considered. At higher frequencies (>500 Hz), the ear canal was the dominant route when either earmuffs or earplugs were worn. However, the dominant route of sound conduction was through the head when both earmuffs and earplugs were worn, through both ear canal and body when a helmet and earmuffs were worn, and through the body when a helmet, earmuffs, and earplugs were worn. It is estimated that a helmet, earmuffs, and earplugs together will reduce the most intense fMRI noise levels experienced by a subject to 60–65 dB SPL. Even greater reductions in noise should be achievable by isolating the body from the surrounding noise field. PMID:11206150

  20. Evaluation of noise pollution level based upon community exposure and response data

    NASA Technical Reports Server (NTRS)

    Edmiston, R. D.

    1972-01-01

    The results and procedures are reported from an evaluation of noise pollution level as a predictor of annoyance, based on aircraft noise exposure and community response data. The measures of noise exposure presented include composite noise rating, noise exposure forecast, noise and number index. A proposed measure as a universal noise exposure measure for noise pollution level (L sub NP) is discussed.

  1. Techniques for Reducing Gun Blast Noise Levels: An Experimental Study

    DTIC Science & Technology

    1981-04-01

    gun muzzle blast noise level were in- vestigated experimentally to determine potential effectiveness and utility for existing major-caliber guns...impact on training and testing operations was to be minimized. Most of the noise reduction techniques that were investigated involve the use of some type ...shock noise level at the earth’s surface varies according to a complicated dependence upon projectile trajectory, projectile speed along the trajectory

  2. Acoustic Noise Alters Selective Attention Processes as Indicated by Direct Current (DC) Brain Potential Changes

    PubMed Central

    Trimmel, Karin; Schätzer, Julia; Trimmel, Michael

    2014-01-01

    Acoustic environmental noise, even of low to moderate intensity, is known to adversely affect information processing in animals and humans via attention mechanisms. In particular, facilitation and inhibition of information processing are basic functions of selective attention. Such mechanisms can be investigated by analyzing brain potentials under conditions of externally directed attention (intake of environmental information) versus internally directed attention (rejection of environmental stimuli and focusing on memory/planning processes). This study investigated brain direct current (DC) potential shifts—which are discussed to represent different states of cortical activation—of tasks that require intake and rejection of environmental information under noise. It was hypothesized that without background noise rejection tasks would show more positive DC potential changes compared to intake tasks and that under noise both kinds of tasks would show positive DC shifts as an expression of cortical inhibition caused by noise. DC potential shifts during intake and rejection tasks were analyzed at 16 standard locations in 45 persons during irrelevant speech or white noise vs. control condition. Without noise, rejection tasks were associated with more positive DC potential changes compared to intake tasks. During background noise, however, this difference disappeared and both kinds of tasks led to positive DC shifts. Results suggest—besides some limitations—that noise modulates selective attention mechanisms by switching to an environmental information processing and noise rejection mode, which could represent a suggested “attention shift”. Implications for fMRI studies as well as for public health in learning and performance environments including susceptible persons are discussed. PMID:25264675

  3. Acoustic noise alters selective attention processes as indicated by direct current (DC) brain potential changes.

    PubMed

    Trimmel, Karin; Schätzer, Julia; Trimmel, Michael

    2014-09-26

    Acoustic environmental noise, even of low to moderate intensity, is known to adversely affect information processing in animals and humans via attention mechanisms. In particular, facilitation and inhibition of information processing are basic functions of selective attention. Such mechanisms can be investigated by analyzing brain potentials under conditions of externally directed attention (intake of environmental information) versus internally directed attention (rejection of environmental stimuli and focusing on memory/planning processes). This study investigated brain direct current (DC) potential shifts-which are discussed to represent different states of cortical activation-of tasks that require intake and rejection of environmental information under noise. It was hypothesized that without background noise rejection tasks would show more positive DC potential changes compared to intake tasks and that under noise both kinds of tasks would show positive DC shifts as an expression of cortical inhibition caused by noise. DC potential shifts during intake and rejection tasks were analyzed at 16 standard locations in 45 persons during irrelevant speech or white noise vs. control condition. Without noise, rejection tasks were associated with more positive DC potential changes compared to intake tasks. During background noise, however, this difference disappeared and both kinds of tasks led to positive DC shifts. Results suggest-besides some limitations-that noise modulates selective attention mechanisms by switching to an environmental information processing and noise rejection mode, which could represent a suggested "attention shift". Implications for fMRI studies as well as for public health in learning and performance environments including susceptible persons are discussed.

  4. Sound pressure level gain in an acoustic metamaterial cavity.

    PubMed

    Song, Kyungjun; Kim, Kiwon; Hur, Shin; Kwak, Jun-Hyuk; Park, Jihyun; Yoon, Jong Rak; Kim, Jedo

    2014-12-11

    The inherent attenuation of a homogeneous viscous medium limits radiation propagation, thereby restricting the use of many high-frequency acoustic devices to only short-range applications. Here, we design and experimentally demonstrate an acoustic metamaterial localization cavity which is used for sound pressure level (SPL) gain using double coiled up space like structures thereby increasing the range of detection. This unique behavior occurs within a subwavelength cavity that is 1/10(th) of the wavelength of the incident acoustic wave, which provides up to a 13 dB SPL gain. We show that the amplification results from the Fabry-Perot resonance of the cavity, which has a simultaneously high effective refractive index and effective impedance. We also experimentally verify the SPL amplification in an underwater environment at higher frequencies using a sample with an identical unit cell size. The versatile scalability of the design shows promising applications in many areas, especially in acoustic imaging and underwater communication.

  5. Sound Pressure Level Gain in an Acoustic Metamaterial Cavity

    NASA Astrophysics Data System (ADS)

    Song, Kyungjun; Kim, Kiwon; Hur, Shin; Kwak, Jun-Hyuk; Park, Jihyun; Yoon, Jong Rak; Kim, Jedo

    2014-12-01

    The inherent attenuation of a homogeneous viscous medium limits radiation propagation, thereby restricting the use of many high-frequency acoustic devices to only short-range applications. Here, we design and experimentally demonstrate an acoustic metamaterial localization cavity which is used for sound pressure level (SPL) gain using double coiled up space like structures thereby increasing the range of detection. This unique behavior occurs within a subwavelength cavity that is 1/10th of the wavelength of the incident acoustic wave, which provides up to a 13 dB SPL gain. We show that the amplification results from the Fabry-Perot resonance of the cavity, which has a simultaneously high effective refractive index and effective impedance. We also experimentally verify the SPL amplification in an underwater environment at higher frequencies using a sample with an identical unit cell size. The versatile scalability of the design shows promising applications in many areas, especially in acoustic imaging and underwater communication.

  6. Sandia National Laboratories' new high level acoustic test facility

    SciTech Connect

    Rogers, J. D.; Hendrick, D. M.

    1989-01-01

    A high intensity acoustic test facility has been designed and is under construction at Sandia National Laboratories in Albuquerque, NM. The chamber is designed to provide an acoustic environment of 154dB (re 20 {mu}Pa) overall sound pressure level over the bandwidth of 50 Hz to 10,000 Hz. The chamber has a volume of 16,000 cubic feet with interior dimensions of 21.6 ft {times} 24.6 ft {times} 30 ft. The construction of the chamber should be complete by the summer of 1990. This paper discusses the design goals and constraints of the facility. The construction characteristics are discussed in detail, as are the acoustic performance design characteristics. The authors hope that this work will help others in designing acoustic chambers. 12 refs., 6 figs.

  7. The noise environment of a school classroom due to the operation of utility helicopters. [acoustic measurements of helicopter noise during flight over building

    NASA Technical Reports Server (NTRS)

    Hilton, D. A.; Pegg, R. J.

    1974-01-01

    Noise measurements under controlled conditions have been made inside and outside of a school building during flyover operations of four different helicopters. The helicopters were operated at a condition considered typical for a police patrol mission. Flyovers were made at an altitude of 500 ft and an airspeed of 45 miles per hour. During these operations acoustic measurements were made inside and outside of the school building with the windows closed and then open. The outside noise measurements during helicopter flyovers indicate that the outside db(A) levels were approximately the same for all test helicopters. For the windows closed case, significant reductions for the inside measured db(A) values were noted for all overflights. These reductions were approximately 20 db(A); similar reductions were noted in other subjective measuring units. The measured internal db(A) levels with the windows open exceeded published classroom noise criteria values; however, for the windows-closed case they are in general agreement with the criteria values.

  8. Noise levels in the vicinity of traffic roundabouts

    NASA Astrophysics Data System (ADS)

    Lewis, P. T.; James, A.

    1980-09-01

    An experimental procedure for analyzing roundabout noise is described. Measurement of the noise from accelerating and decelerating traffic streams on the approach roads to roundabouts at a total of 70 positions at three sites are reported together with a simulation study of noise from central island traffic. The results show that, in general, noise from the accelerating traffic streams is within ±1 dB(A) of the free flow level on the same road and that the noise from the decelerating stream is equal to or less than the free flow level. The propagation of noise from the central island is expressed in the form of a nomogram. Good agreement between predicted and measured levels was found.

  9. Assessment at full scale of nozzle/wing geometry effects on OTW aero-acoustic characteristics. [short takeoff aircraft noise

    NASA Technical Reports Server (NTRS)

    Groesbeck, D.; Vonglahn, U.

    1979-01-01

    The effects on acoustic characteristics of nozzle type and location on a wing for STOL engine over-the-wing configurations are assessed at full scale on the basis of model-scale data. Three types of nozzle configurations are evaluated: a circular nozzle with external deflector mounted above the wing, a slot nozzle with external deflector mounted on the wing and a slot nozzle mounted on the wing. Nozzle exhaust plane locations with respect to the wing leading edge are varied from 10 to 46 percent chord (flaps retracted) with flap angles of 20 (takeoff altitude) and 60 (approach attitude). Perceived noise levels (PNL) are calculated as a function of flyover distance at 152 m altitude. From these plots, static EPNL values, defined as flyover relative noise levels, are calculated and plotted as a function of lift and thrust ratios. From such plots the acoustic benefits attributable to variations in nozzle/deflector/wing geometry at full scale are assessed for equal aerodynamic performance.

  10. Acoustic flight tests of rotorcraft noise-abatement approaches using local differential GPS guidance

    NASA Technical Reports Server (NTRS)

    Chen, Robert T. N.; Hindson, William S.; Mueller, Arnold W.

    1995-01-01

    This paper presents the test design, instrumentation set-up, data acquisition, and the results of an acoustic flight experiment to study how noise due to blade-vortex interaction (BVI) may be alleviated. The flight experiment was conducted using the NASA/Army Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) research helicopter. A Local Differential Global Positioning System (LDGPS) was used for precision navigation and cockpit display guidance. A laser-based rotor state measurement system on board the aircraft was used to measure the main rotor tip-path-plane angle-of-attack. Tests were performed at Crows Landing Airfield in northern California with an array of microphones similar to that used in the standard ICAO/FAA noise certification test. The methodology used in the design of a RASCAL-specific, multi-segment, decelerating approach profile for BVI noise abatement is described, and the flight data pertaining to the flight technical errors and the acoustic data for assessing the noise reduction effectiveness are reported.

  11. Study of thermal and acoustic noise interferences in low stiffness atomic force microscope cantilevers and characterization of their dynamic properties

    SciTech Connect

    Boudaoud, Mokrane; Haddab, Yassine; Le Gorrec, Yann; Lutz, Philippe

    2012-01-15

    The atomic force microscope (AFM) is a powerful tool for the measurement of forces at the micro/nano scale when calibrated cantilevers are used. Besides many existing calibration techniques, the thermal calibration is one of the simplest and fastest methods for the dynamic characterization of an AFM cantilever. This method is efficient provided that the Brownian motion (thermal noise) is the most important source of excitation during the calibration process. Otherwise, the value of spring constant is underestimated. This paper investigates noise interference ranges in low stiffness AFM cantilevers taking into account thermal fluctuations and acoustic pressures as two main sources of noise. As a result, a preliminary knowledge about the conditions in which thermal fluctuations and acoustic pressures have closely the same effect on the AFM cantilever (noise interference) is provided with both theoretical and experimental arguments. Consequently, beyond the noise interference range, commercial low stiffness AFM cantilevers are calibrated in two ways: using the thermal noise (in a wide temperature range) and acoustic pressures generated by a loudspeaker. We then demonstrate that acoustic noises can also be used for an efficient characterization and calibration of low stiffness AFM cantilevers. The accuracy of the acoustic characterization is evaluated by comparison with results from the thermal calibration.

  12. Effects of low levels of road traffic noise during the night: a laboratory study on number of events, maximum noise levels and noise sensitivity

    NASA Astrophysics Data System (ADS)

    Öhrström, E.

    1995-01-01

    The objective of the laboratory study presented here was to elucidate the importance of the number of noise events of a relatively low maximum noise level for sleep disturbance effects (body movements, subjective sleep quality, mood and performance). Twelve test persons slept eight nights under home-like laboratory settings. During four of these nights, each test person was exposed to 16, 32, 64 and 128 noise events respectively from recorded road traffic noise at a maximum noise level of 45 dB(A). All test persons (aged 20-42 years) considered themselves rather or very sensitive towards noise. The results show a significant decrease in subjective sleep quality at 32 noise events per night. At 64 noise events, 50% of the test persons experienced difficulties in falling asleep and, as compared with quiet nights, the time required to fall asleep was on average 12 minutes longer. The occurrence of body movements was significantly related to the reported number of awakenings, and the number of body movements was three times higher during the noisy periods of the night as compared with the quiet periods, indicating acute noise effects. The results of a vigilance test indicate that noise during the night might prolong the time needed to solve the test. Finally, and regardless of number of noise events, a significant increase in tiredness during the day was found after nights with noise exposure. In the paper comparisons are also made with earlier experiments using maximum noise levels of 50 and 60 dB(A).

  13. Investigations of internal noise levels for different target sizes, contrasts, and noise structures

    NASA Astrophysics Data System (ADS)

    Han, Minah; Choi, Shinkook; Baek, Jongduk

    2014-03-01

    To describe internal noise levels for different target sizes, contrasts, and noise structures, Gaussian targets with four different sizes (i.e., standard deviation of 2,4,6 and 8) and three different noise structures(i.e., white, low-pass, and highpass) were generated. The generated noise images were scaled to have standard deviation of 0.15. For each noise type, target contrasts were adjusted to have the same detectability based on NPW, and the detectability of CHO was calculated accordingly. For human observer study, 3 trained observers performed 2AFC detection tasks, and correction rate, Pc, was calculated for each task. By adding proper internal noise level to numerical observer (i.e., NPW and CHO), detectability of human observer was matched with that of numerical observers. Even though target contrasts were adjusted to have the same detectability of NPW observer, detectability of human observer decreases as the target size increases. The internal noise level varies for different target sizes, contrasts, and noise structures, demonstrating different internal noise levels should be considered in numerical observer to predict the detection performance of human observer.

  14. [Effects of peak levels and number of noise impulses on hearing among forge hammering workers].

    PubMed

    Suvorov, G A; Denisov, E I; Antipin, V G; Kharitonov, V I; Starck, Iu; Pyykko, I; Toppila, E

    2002-01-01

    The work was aimed (1) to compare actual and expected values of hearing loss in forge hammering workers, using risk evaluation patterns based on impulse noise measurements, and (2) to simulate harmful hearing changes caused by impulse noise. Study of exposure to noise and hearing loss covered forge hammering workers in 2 major blacksmith workshops of automobile enterprise, where equivalent levels of acoustic pressure (104 and 106 dB) were equal, but peak levels and impalse degrees reliably differed. Hearing thresholds for 2 selected groups of workers (97 and 235 subjects) were evaluated. When compared, actual and expected values of hearing loss calculated according to ISO standard appeared different with excess of 1 dB and 3 dB for the workers in shops 1 and 2 respectively. Excessive hearing loss corresponds to noise exposure increased by 3.5 years. Hearing loss in the workers subjected to less impulsive noise were readily forecasted by ISO standard 1999-1990. Hearing loss in the workers subjected to more impulsive noise were in reliable correlation with combination of peak level and impulses number.

  15. A Noise Level Prediction Method Based on Electro-Mechanical Frequency Response Function for Capacitors

    PubMed Central

    Zhu, Lingyu; Ji, Shengchang; Shen, Qi; Liu, Yuan; Li, Jinyu; Liu, Hao

    2013-01-01

    The capacitors in high-voltage direct-current (HVDC) converter stations radiate a lot of audible noise which can reach higher than 100 dB. The existing noise level prediction methods are not satisfying enough. In this paper, a new noise level prediction method is proposed based on a frequency response function considering both electrical and mechanical characteristics of capacitors. The electro-mechanical frequency response function (EMFRF) is defined as the frequency domain quotient of the vibration response and the squared capacitor voltage, and it is obtained from impulse current experiment. Under given excitations, the vibration response of the capacitor tank is the product of EMFRF and the square of the given capacitor voltage in frequency domain, and the radiated audible noise is calculated by structure acoustic coupling formulas. The noise level under the same excitations is also measured in laboratory, and the results are compared with the prediction. The comparison proves that the noise prediction method is effective. PMID:24349105

  16. Pilot Survey of Subway and Bus Stop Noise Levels

    PubMed Central

    Neitzel, Richard; Barrera, Marissa A.; Akram, Muhammad

    2006-01-01

    Excessive noise exposure is a serious global urban health problem, adversely affecting millions of people. One often cited source of urban noise is mass transit, particularly subway systems. As a first step in determining risk within this context, we recently conducted an environmental survey of noise levels of the New York City transit system. Over 90 noise measurements were made using a sound level meter. Average and maximum noise levels were measured on subway platforms, and maximum levels were measured inside subway cars and at several bus stops for comparison purposes. The average noise level measured on the subway platforms was 86 ± 4 dBA (decibel-A weighting). Maximum levels of 106, 112, and 89 dBA were measured on subway platforms, inside subway cars, and at bus stops, respectively. These results indicate that noise levels in subway and bus stop environments have the potential to exceed recommended exposure guidelines from the World Health Organization (WHO) and U.S. Environmental Protection Agency (EPA), given sufficient exposure duration. Risk reduction strategies following the standard hierarchy of control measures should be applied, where feasible, to reduce subway noise exposure. PMID:16802179

  17. Effects of Tidal Turbine Noise on Fish Task 2.1.3.2: Effects on Aquatic Organisms: Acoustics/Noise - Fiscal Year 2011 - Progress Report - Environmental Effects of Marine and Hydrokinetic Energy

    SciTech Connect

    Halvorsen, Michele B.; Carlson, Thomas J.; Copping, Andrea E.

    2011-09-30

    Naturally spawning stocks of Chinook salmon (Oncorhynchus tshawytscha) that utilize Puget Sound are listed as threatened (http://www.nwr.noaa.gov/ESA-Salmon-Listings/Salmon-Populations/ Chinook/CKPUG.cfm). Plans exist for prototype tidal turbines to be deployed into their habitat. Noise is known to affect fish in many ways, such as causing a threshold shift in auditory sensitivity or tissue damage. The characteristics of noise, its spectra and level, are important factors that influence the potential for the noise to injure fish. For example, the frequency range of the tidal turbine noise includes the audiogram (frequency range of hearing) of most fish. This study (Effects on Aquatic Organisms, Subtask 2.1.3.2: Acoustics) was performed during FY 2011 to determine if noise generated by a 6-m-diameter open-hydro turbine might affect juvenile Chinook salmon hearing or cause barotrauma. After they were exposed to simulated tidal turbine noise, the hearing of juvenile Chinook salmon was measured and necropsies performed to check for tissue damage. Experimental groups were (1) noise exposed, (2) control (the same handling as treatment fish but without exposure to tidal turbine noise), and (3) baseline (never handled). Preliminary results indicate that low levels of tissue damage may have occurred but that there were no effects of noise exposure on the auditory systems of the test fish.

  18. Definition of 1992 Technology Aircraft Noise Levels and the Methodology for Assessing Airplane Noise Impact of Component Noise Reduction Concepts

    NASA Technical Reports Server (NTRS)

    Kumasaka, Henry A.; Martinez, Michael M.; Weir, Donald S.

    1996-01-01

    This report describes the methodology for assessing the impact of component noise reduction on total airplane system noise. The methodology is intended to be applied to the results of individual study elements of the NASA-Advanced Subsonic Technology (AST) Noise Reduction Program, which will address the development of noise reduction concepts for specific components. Program progress will be assessed in terms of noise reduction achieved, relative to baseline levels representative of 1992 technology airplane/engine design and performance. In this report, the 1992 technology reference levels are defined for assessment models based on four airplane sizes - an average business jet and three commercial transports: a small twin, a medium sized twin, and a large quad. Study results indicate that component changes defined as program final goals for nacelle treatment and engine/airframe source noise reduction would achieve from 6-7 EPNdB reduction of total airplane noise at FAR 36 Stage 3 noise certification conditions for all of the airplane noise assessment models.

  19. The effect of different cochlear implant microphones on acoustic hearing individuals’ binaural benefits for speech perception in noise

    PubMed Central

    Aronoff, Justin M.; Freed, Daniel J.; Fisher, Laurel M.; Pal, Ivan; Soli, Sigfrid D.

    2011-01-01

    directional microphone when the speech and masker were spatially separated, emphasizing the importance of measuring binaural benefits separately for each HRTF. Evaluation of binaural benefits indicated that binaural squelch and spatial release from masking were found for all HRTFs and binaural summation was found for all but one HRTF, although binaural summation was less robust than the other types of binaural benefits. Additionally, the results indicated that neither interaural time nor level cues dominated binaural benefits for the normal hearing participants. Conclusions This study provides a means to measure the degree to which cochlear implant microphones affect acoustic hearing with respect to speech perception in noise. It also provides measures that can be used to evaluate the independent contributions of interaural time and level cues. These measures provide tools that can aid researchers in understanding and improving binaural benefits in acoustic hearing individuals listening via cochlear implant microphones. PMID:21412155

  20. Near noise field characteristics of Nike rocket motors for application to space vehicle payload acoustic qualification

    NASA Technical Reports Server (NTRS)

    Hilton, D. A.; Bruton, D.

    1977-01-01

    Results of a series of noise measurements that were made under controlled conditions during the static firing of two Nike solid propellant rocket motors are presented. The usefulness of these motors as sources for general spacecraft noise testing was assessed, and the noise expected in the cargo bay of the orbiter was reproduced. Brief descriptions of the Nike motor, the general procedures utilized for the noise tests, and representative noise data including overall sound pressure levels, one third octave band spectra, and octave band spectra were reviewed. Data are presented on two motors of different ages in order to show the similarity between noise measurements made on motors having different loading dates. The measured noise from these tests is then compared to that estimated for the space shuttle orbiter cargo bay.

  1. Equal autophonic level curves under different room acoustics conditions.

    PubMed

    Pelegrín-García, David; Fuentes-Mendizábal, Oier; Brunskog, Jonas; Jeong, Cheol-Ho

    2011-07-01

    The indirect auditory feedback from one's own voice arises from sound reflections at the room boundaries or from sound reinforcement systems. The relative variations of indirect auditory feedback are quantified through room acoustic parameters such as the room gain and the voice support, rather than the reverberation time. Fourteen subjects matched the loudness level of their own voice (the autophonic level) to that of a constant and external reference sound, under different synthesized room acoustics conditions. The matching voice levels are used to build a set of equal autophonic level curves. These curves give an indication of the amount of variation in voice level induced by the acoustic environment as a consequence of the sidetone compensation or Lombard effect. In the range of typical rooms for speech, the variations in overall voice level that result in a constant autophonic level are on the order of 2 dB, and more than 3 dB in the 4 kHz octave band. By comparison of these curves with previous studies, it is shown that talkers use acoustic cues other than loudness to adjust their voices when speaking in different rooms.

  2. Acoustic noise reduction. January 1970-November 1988 (Citations from the US Patent data base). Report for January 1970-November 1988

    SciTech Connect

    Not Available

    1988-12-01

    This bibliography contains citations of selected patents concerning methods, devices, and materials for acoustic-noise reduction. Included are noise-reduction techniques for engines, turbines, machinery, motor vehicles, pumps, aircraft cabins, and compressors. (Contains 189 citations fully indexed and including a title list.)

  3. Relationship between Aircraft Noise Contour Area and Noise Levels at Certification Points

    NASA Technical Reports Server (NTRS)

    Powell, Clemans A.

    2003-01-01

    The use of sound exposure level contour area reduction has been proposed as an alternative or supplemental metric of progress and success for the NASA Quiet Aircraft Technology program, which currently uses the average of predicted noise reductions at three community locations. As the program has expanded to include reductions in airframe noise as well as reduction due to optimization of operating procedures for lower noise, there is concern that the three-point methodology may not represent a fair measure of benefit to airport communities. This paper addresses several topics related to this proposal: (1) an analytical basis for a relationship between certification noise levels and noise contour areas for departure operations is developed, (2) the relationship between predicted noise contour area and the noise levels measured or predicted at the certification measurement points is examined for a wide range of commercial and business aircraft, and (3) reductions in contour area for low-noise approach scenarios are predicted and equivalent reductions in source noise are determined.

  4. Noise Control in Space Shuttle Orbiter

    NASA Technical Reports Server (NTRS)

    Goodman, Jerry R.

    2009-01-01

    Acoustic limits in habitable space enclosures are required to ensure crew safety, comfort, and habitability. Noise control is implemented to ensure compliance with the acoustic requirements. The purpose of this paper is to describe problems with establishing acoustic requirements and noise control efforts, and present examples of noise control treatments and design applications used in the Space Shuttle Orbiter. Included is the need to implement the design discipline of acoustics early in the design process, and noise control throughout a program to ensure that limits are met. The use of dedicated personnel to provide expertise and oversight of acoustic requirements and noise control implementation has shown to be of value in the Space Shuttle Orbiter program. It is concluded that to achieve acceptable and safe noise levels in the crew habitable space, early resolution of acoustic requirements and implementation of effective noise control efforts are needed. Management support of established acoustic requirements and noise control efforts is essential.

  5. Intrinsic Noise Level of Noise Cross-Correlation Functions and its Implication to Source Population of Ambient noises

    NASA Astrophysics Data System (ADS)

    Chen, Ying-Nien; Gung, Yuancheng; Chiao, Ling-Yun; Rhie, Junkee

    2017-01-01

    SUMMARYWe present a quantitative procedure to evaluate the intrinsic <span class="hlt">noise</span> <span class="hlt">level</span> (INL) of the <span class="hlt">noise</span> cross-correlation function (NCF). The method is applied to realistic NCFs derived from the continuous data recorded by the seismic arrays in Taiwan and Korea. The obtained temporal evolution of NCF <span class="hlt">noise</span> <span class="hlt">level</span> follows fairly the prediction of the theoretical formulation, confirming the feasibility of the method. We then apply the obtained INL to the assessment of data quality and the source characteristics of ambient <span class="hlt">noise</span>. We show that the INL-based signal-to-<span class="hlt">noise</span> ratio provides an exact measure for the true <span class="hlt">noise</span> <span class="hlt">level</span> within the NCF and better resolving power for the NCF quality, and such measurement can be implemented to any time windows of the NCFs to evaluate the quality of overtones or coda waves. Moreover, since NCF amplitudes are influenced by both the population and excitation strengths of <span class="hlt">noises</span>, while INL is primarily sensitive to the overall source population, with information from both measurements, we may better constrain the source characteristics of seismic ambient <span class="hlt">noises</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20080047683','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20080047683"><span>A Numerical Investigation of Turbine <span class="hlt">Noise</span> Source Hierarchy and Its <span class="hlt">Acoustic</span> Transmission Characteristics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>VanZante, Dale; Envia, Edmane</p> <p>2008-01-01</p> <p>Understanding the relative importance of the various turbine <span class="hlt">noise</span> generation mechanisms and the characteristics of the turbine <span class="hlt">acoustic</span> transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine <span class="hlt">noise</span> signature. A computationally based investigation has been undertaken to help guide the development of a turbine <span class="hlt">noise</span> prediction capability that does not rely on empiricism. The investigation relies on highly detailed numerical simulations of the unsteady flowfield inside a modern high-pressure turbine (HPT). The simulations are developed using TURBO, which is an unsteady Reynolds-averaged Navier-Stokes (URANS) code capable of multi-stage simulations. The purpose of this study is twofold. First, to determine an estimate of the relative importance of the contributions to the coherent part of the <span class="hlt">acoustic</span> signature of a turbine from the three potential sources of turbine <span class="hlt">noise</span> generation, namely, blade-row viscous interaction, potential field interaction, and entropic source associated with the interaction of the blade rows with the temperature nonuniformities caused by the incomplete mixing of the hot fluid and the cooling flow. Second, to develop an understanding of the turbine <span class="hlt">acoustic</span> transmission characteristics and to assess the applicability of existing empirical and analytical transmission loss models to realistic geometries and flow conditions for modern turbine designs. The investigation so far has concentrated on two simulations: (1) a single-stage HPT and (2) a two-stage HPT and the associated inter-turbine duct/strut segment. The simulations are designed to resolve up to the second harmonic of the blade passing frequency tone in accordance with accepted rules for second order solvers like TURBO. The calculations include blade and vane cooling flows and a radial profile of pressure and temperature at the turbine inlet. The calculation can be modified later to include the combustor pattern factor at the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MS%26E..180a2121R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MS%26E..180a2121R"><span>Measurement of <span class="hlt">Noise</span> <span class="hlt">Level</span> in Enumeration Station in Rubber Industry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rizkya, I.; Syahputri, K.; Sari, R. M.; Siregar, I.</p> <p>2017-03-01</p> <p>This research was conducted in companies engaged in the production of crumb rubber. In the rubber industry, the potential <span class="hlt">noise</span> occurs in the enumeration station. Stations enumeration use machine and equipment that potentially generated <span class="hlt">noise</span>. <span class="hlt">Noise</span> can be defined as an unwanted sound because it does not fit the context of space and time so that may interfere with the comfort and human health. The <span class="hlt">noise</span> <span class="hlt">level</span> measured at random during the initial observation station enumeration is 101.8 dB. This value has exceeded the Threshold Limit Value (TLV) Kep-51 / MEN / 1999 and SNI No. 16-7063-2004 so research must be done to measure the <span class="hlt">level</span> of <span class="hlt">noise</span> in the enumeration station. Quantitative methods used in the study. Observations made with the calculation method of equivalent <span class="hlt">noise</span> <span class="hlt">level</span>. Observations were made on six measurement points for one shift for three days. The results showed the <span class="hlt">noise</span> <span class="hlt">level</span> over the Threshold Limit Value is equal to 85 dBA/8 hours. Based on the measurement results, the whole point of observation was far above the threshold Limit Value (TLV). The highest <span class="hlt">noise</span> <span class="hlt">level</span> equivalent is in the observation point 6 with a value of 102, 21 dB.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22507599','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22507599"><span><span class="hlt">Acoustic</span> evaluation and adjustment of an open-plan office through architectural design and <span class="hlt">noise</span> control.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Passero, Carolina Reich Marcon; Zannin, Paulo Henrique Trombetta</p> <p>2012-11-01</p> <p>Arranging office space into a single open room offers advantages in terms of easy exchange of information and interaction among coworkers, but reduces privacy and <span class="hlt">acoustic</span> comfort. Thus, the purpose of this work was to evaluate the <span class="hlt">acoustic</span> quality of a real open-plan office and to propose changes in the room to improve the <span class="hlt">acoustic</span> conditioning of this office. The computational model of the office under study was calibrated based on RT and STI measurements. Predictions were made of the RT and STI, which generated the radius of distraction r(D), and the rate of spatial decay of sound pressure <span class="hlt">levels</span> per distance doubling DL(2) in the real conditions of the office and after modifications of the room. The insertion of dividers between work stations and an increase in the ceiling's sound absorption improved the <span class="hlt">acoustic</span> conditions in the office under study.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27106340','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27106340"><span>Military jet <span class="hlt">noise</span> source imaging using multisource statistically optimized near-field <span class="hlt">acoustical</span> holography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wall, Alan T; Gee, Kent L; Neilsen, Tracianne B; McKinley, Richard L; James, Michael M</p> <p>2016-04-01</p> <p>The identification of <span class="hlt">acoustic</span> sources is critical to targeted <span class="hlt">noise</span> reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of <span class="hlt">acoustic</span> sources from a tactical jet using near-field <span class="hlt">acoustical</span> holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field <span class="hlt">acoustical</span> holography (M-SONAH) is used to reconstruct apparent source distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated source location; sources farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped source regions, which is a phenomenon relatively recently reported for full-scale jets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1012409','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1012409"><span><span class="hlt">Noise</span> <span class="hlt">Levels</span> in the Operating Room</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2001-10-01</p> <p>CRNA vigilance is crucial to the well-being of patients, and if the cause of the <span class="hlt">noise</span> can be identified and corrected , CRNAs in the future...64.6 52.2 85.5 107.0 56.2 23 Open shoulder GETA 64.3 48.3 88.9 112.6 54.6 24 Cancelled (before induction) 66.8 50.6 95.0 117.2 53.9 25 Osteotomy ...acromioplasty Knee arthroscopy Knee arthroscopy Knee arthroscopy Finger pinning Wrist pinning Open shoulder Cancelled before inducing Osteotomy ACL</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25175843','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25175843"><span>Reduction of classroom <span class="hlt">noise</span> <span class="hlt">levels</span> using group contingencies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ring, Brandon M; Sigurdsson, Sigurdur O; Eubanks, Sean L; Silverman, Kenneth</p> <p>2014-01-01</p> <p>The therapeutic workplace is an employment-based abstinence reinforcement intervention for unemployed drug users where trainees receive on-the-job employment skills training in a classroom setting. The study is an extension of prior therapeutic workplace research, which suggested that trainees frequently violated <span class="hlt">noise</span> standards. Participants received real-time graphed feedback of <span class="hlt">noise</span> <span class="hlt">levels</span> and had the opportunity to earn monetary group reinforcement for maintaining a low number of <span class="hlt">noise</span> violations. Results suggested that feedback and monetary reinforcement reduced the number of <span class="hlt">noise</span> violations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994JSV...177..289W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994JSV...177..289W"><span><span class="hlt">Acoustic</span> Performance Of New Designs Of Traffic <span class="hlt">Noise</span> Barriers: Full Scale Tests</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watts, G. R.; Crombie, D. H.; Hothersall, D. C.</p> <p>1994-10-01</p> <p>Full scale tests of <span class="hlt">acoustical</span> performance are reported on a range of promising traffic <span class="hlt">noise</span> barrier shapes which had previously been identified by mathematical and scale modelling work. The designs chosen for testing were T-shaped, multiple edge barriers and double barriers. A test facility was established at the Transport Research Laboratory (TRL) in order to examine effectiveness under full scale conditions. This consisted of a 20 m length of <span class="hlt">noise</span> barrier with interchangeable barrier panels, a large flat asphalt surface and a transportable speaker system capable of sufficient output to represent typical traffic <span class="hlt">noise</span>. Screening performance was measured up to 80 m behind the barriers over a flat grassland area and at heights above the ground of 1·5 and 4·5 m. It was concluded that the average increase in <span class="hlt">acoustic</span> screening of 2 m high T-shaped, multiple edge and double barriers compared with a simple plane reflecting barrier of identical overall height ranged from 1·4 to 3·6dB(A) depending on detailed design. It was suggested that a full scale test of a promising design should be carried out at a suitable highway location in order to validate fully these test results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5121232','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5121232"><span>Long Term Memory for <span class="hlt">Noise</span>: Evidence of Robust Encoding of Very Short Temporal <span class="hlt">Acoustic</span> Patterns</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Viswanathan, Jayalakshmi; Rémy, Florence; Bacon-Macé, Nadège; Thorpe, Simon J.</p> <p>2016-01-01</p> <p>Recent research has demonstrated that humans are able to implicitly encode and retain repeating patterns in meaningless auditory <span class="hlt">noise</span>. Our study aimed at testing the robustness of long-term implicit recognition memory for these learned patterns. Participants performed a cyclic/non-cyclic discrimination task, during which they were presented with either 1-s cyclic <span class="hlt">noises</span> (CNs) (the two halves of the <span class="hlt">noise</span> were identical) or 1-s plain random <span class="hlt">noises</span> (Ns). Among CNs and Ns presented once, target CNs were implicitly presented multiple times within a block, and implicit recognition of these target CNs was tested 4 weeks later using a similar cyclic/non-cyclic discrimination task. Furthermore, robustness of implicit recognition memory was tested by presenting participants with looped (shifting the origin) and scrambled (chopping sounds into 10− and 20-ms bits before shuffling) versions of the target CNs. We found that participants had robust implicit recognition memory for learned <span class="hlt">noise</span> patterns after 4 weeks, right from the first presentation. Additionally, this memory was remarkably resistant to <span class="hlt">acoustic</span> transformations, such as looping and scrambling of the sounds. Finally, implicit recognition of sounds was dependent on participant's discrimination performance during learning. Our findings suggest that meaningless temporal features as short as 10 ms can be implicitly stored in long-term auditory memory. Moreover, successful encoding and storage of such fine features may vary between participants, possibly depending on individual attention and auditory discrimination abilities. Significance Statement Meaningless auditory patterns could be implicitly encoded and stored in long-term memory.<span class="hlt">Acoustic</span> transformations of learned meaningless patterns could be implicitly recognized after 4 weeks.Implicit long-term memories can be formed for meaningless auditory features as short as 10 ms.Successful encoding and long-term implicit recognition of meaningless patterns may</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2707461','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2707461"><span><span class="hlt">Noise</span> <span class="hlt">Levels</span> Associated With New York City's Mass Transit Systems</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gershon, Robyn R. M.; Zeltser, Marina; Canton, Allison; Akram, Muhammad</p> <p>2009-01-01</p> <p>Objectives. We measured <span class="hlt">noise</span> <span class="hlt">levels</span> associated with various forms of mass transit and compared them to exposure guidelines designed to protect against <span class="hlt">noise</span>-induced hearing loss. Methods. We used <span class="hlt">noise</span> dosimetry to measure time-integrated <span class="hlt">noise</span> <span class="hlt">levels</span> in a representative sample of New York City mass transit systems (subways, buses, ferries, tramway, and commuter railways) aboard transit vehicles and at vehicle boarding platforms or terminals during June and July 2007. Results. Of the transit types evaluated, subway cars and platforms had the highest associated equivalent continuous average (Leq) and maximum <span class="hlt">noise</span> <span class="hlt">levels</span>. All transit types had Leq <span class="hlt">levels</span> appreciably above 70 A-weighted decibels, the threshold at which <span class="hlt">noise</span>-induced hearing loss is considered possible. Conclusions. Mass transit <span class="hlt">noise</span> exposure has the potential to exceed limits recommended by the World Health Organization and the US Environmental Protection Agency and thus cause <span class="hlt">noise</span>-induced hearing loss among riders of all forms of mass transit given sufficient exposure durations. Environmental noise–control efforts in mass transit and, in cases in which controls are infeasible, the use of personal hearing protection would benefit the ridership's hearing health. PMID:19542046</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850022454','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850022454"><span>Effects of propeller rotation direction on airplane interior <span class="hlt">noise</span> <span class="hlt">levels</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Willis, C. M.; Mayes, W. H.; Daniels, E. F.</p> <p>1985-01-01</p> <p>Interior <span class="hlt">noise</span> measurements for upsweeping and downsweeping movement of the propeller blade tips past the fuselage were made on a twin-engine airplane and on two simplified fuselage models. Changes in interior <span class="hlt">noise</span> <span class="hlt">levels</span> of as much as 8 dB reversal of propeller rotation direction were measured for some configurations and test conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19800019333','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19800019333"><span><span class="hlt">Noise</span> <span class="hlt">levels</span> near streets, effectiveness and cost abatement measures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lang, J.</p> <p>1980-01-01</p> <p>During the years 1975-1978, research was carried concerning the current <span class="hlt">noise</span> <span class="hlt">levels</span> near streets, the annoyance felt by the population, possible <span class="hlt">noise</span> abatement measures for these streets, and the economic impact of such measures. The results of the research are summarized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=noise+AND+environment&pg=4&id=EJ736160','ERIC'); return false;" href="http://eric.ed.gov/?q=noise+AND+environment&pg=4&id=EJ736160"><span><span class="hlt">Acoustical</span> Barriers in Classrooms: The Impact of <span class="hlt">Noise</span> on Performance in the Classroom</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Dockrell, Julie E.; Shield, Bridget M.</p> <p>2006-01-01</p> <p>There is general concern about the <span class="hlt">levels</span> of <span class="hlt">noise</span> that children are exposed to in classroom situations. The article reports the results of a study that explores the effects of typical classroom <span class="hlt">noise</span> on the performance of primary school children on a series of literacy and speed tasks. One hundred and fifty-eight children in six Year 3 classes…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21192960','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21192960"><span><span class="hlt">Noise</span> exposure during early development influences the <span class="hlt">acoustic</span> startle reflex in adult rats.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rybalko, Natalia; Bureš, Zbyněk; Burianová, Jana; Popelář, Jiří; Grécová, Jolana; Syka, Josef</p> <p>2011-03-28</p> <p><span class="hlt">Noise</span> exposure during the critical period of postnatal development in rats results in anomalous processing of <span class="hlt">acoustic</span> stimuli in the adult auditory system. In the present study, the behavioral consequences of an acute <span class="hlt">acoustic</span> trauma in the critical period are assessed in adult rats using the <span class="hlt">acoustic</span> startle reflex (ASR) and prepulse inhibition (PPI) of ASR. Rat pups (strain Long-Evans) were exposed to broad-band <span class="hlt">noise</span> of 125 dB SPL for 8 min on postnatal day 14; at the age of 3-5 months, ASR and PPI of ASR were examined and compared with those obtained in age-matched controls. In addition, hearing thresholds were measured in all animals by means of auditory brainstem responses. The results show that although the hearing thresholds in both groups of animals were not different, a reduced strength of the startle reflex was observed in exposed rats compared with controls. The efficacy of PPI in exposed and control rats was also markedly different. In contrast to control rats, in which an increase in prepulse intensity was accompanied by a consistent increase in the efficacy of PPI, the PPI function in the exposed animals was characterized by a steep increase in inhibitory efficacy at low prepulse intensities of 20-30 dB SPL. A further increase of prepulse intensity up to 60-70 dB SPL caused only a small and insignificant change of PPI. Our findings demonstrate that brief <span class="hlt">noise</span> exposure in rat pups results in altered behavioral responses to sounds in adulthood, indicating anomalies in intensity coding and loudness perception.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S41A2707A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S41A2707A"><span>Ambient <span class="hlt">Noise</span> Surface Wave Tomography for Geotechnical Monitoring Using "Large N" Distributed <span class="hlt">Acoustic</span> Sensing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ajo Franklin, J. B.; Lindsey, N.; Martin, E. R.; Wagner, A. M.; Robertson, M.; Bjella, K.; Gelvin, A.; Ulrich, C.; Wu, Y.; Freifeld, B. M.; Daley, T. M.; Dou, S.</p> <p>2015-12-01</p> <p>Surface wave tomography using ambient <span class="hlt">noise</span> sources has found broad application at the regional scale but has not been adopted fully for geotechnical applications despite the abundance of <span class="hlt">noise</span> sources in this context. The recent development of Distributed <span class="hlt">Acoustic</span> Sensing (DAS) provides a clear path for inexpensively recording high spatial resolution (< 1m sampling) surface wave data in the context of infrastructure monitoring over significant spatial domains (10s of km). Infrastructure monitoring is particularly crucial in the context of high-latitude installations where a changing global climate can trigger reductions in soil strength due to permafrost thaw. DAS surface wave monitoring systems, particularly those installed in/near transport corridors and coupled to ambient <span class="hlt">noise</span> inversion algorithms, could be a critical "early warning" system to detect zones of decreased shear strength before failure. We present preliminary ambient <span class="hlt">noise</span> tomography results from a 1.3 km continuously recording subsurface DAS array used to record traffic <span class="hlt">noise</span> next to an active road in Fairbanks, AK. The array, depolyed at the Farmer's Loop Permafrost Test Station, was designed as a narrow 2D array and installed via trenching at ~30 cm. We develop a pre-processing and QC approach to analyze the large resulting volume of data, equivalent to a 1300 geophone array sampled at 1 khz. We utilize automated dispersion analysis and a quasi-2D MC inversion to generate a shear wave velocity profile underneath the road in a region of discontinuous permafrost. The results are validated against a high-resolution ERT survey as well as direct-push data on ice content. We also compare vintages of ambient <span class="hlt">noise</span> DAS data to evaluate the short-term repeatability of the technique in the face of changing <span class="hlt">noise</span> environments. The resulting dataset demonstrates the utility of using DAS for real-time shear-modulus monitoring in support of critical infrastructure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16018467','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16018467"><span><span class="hlt">Acoustic</span> characteristics of an electrodynamic planar digital loudspeaker using <span class="hlt">noise</span> shaping technology.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hayama, Atsushi; Furihata, Kenji; Asano, David K; Yanagisawa, Takesaburo</p> <p>2005-06-01</p> <p>The present study extends our previous work [Furihata et al., J. <span class="hlt">Acoust</span>. Soc. Am. 114, 174-184 (2003)] by investigating our electrodynamic planar loudspeaker when driven by a 12 bit digital signal with <span class="hlt">noise</span> shaping. Changing the structure of the loudspeaker can lead to improvement, but in this paper improvements that can be made using signal processing are investigated. Results show that the digital loudspeaker demonstrated good linearity over its 84 dB dynamic range from 40 Hz to 10 kHz. This shows that a 12 bit digital loudspeaker which is equivalent to a 16 bit one is possible.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JMMM..426..779N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JMMM..426..779N"><span>Magnetic Barkhausen <span class="hlt">noise</span> and magneto <span class="hlt">acoustic</span> emission in pressure vessel steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Neyra Astudillo, Miriam Rocío; López Pumarega, María Isabel; Núñez, Nicolás Marcelo; Pochettino, Alberto; Ruzzante, José</p> <p>2017-03-01</p> <p>Magnetic Barkhausen <span class="hlt">Noise</span> (MBN) and Magneto <span class="hlt">Acoustic</span> Emission (MAE) were studied in A508 Class II forged steel used for pressure vessels in nuclear power stations. The magnetic experimental determinations were completed with a macro graphic study of sulfides and the texture analysis of the material. The analysis of these results allows us to determine connections between the magnetic anisotropy, texture and microstructure of the material. Results clearly suggest that the plastic flow direction is different from the forging direction indicated by the material supplier</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..MARM46012E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..MARM46012E"><span>Towards Truly Quiet MRI: animal MRI magnetic field gradients as a test platform for <span class="hlt">acoustic</span> <span class="hlt">noise</span> reduction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Edelstein, William; El-Sharkawy, Abdel-Monem</p> <p>2013-03-01</p> <p>Clinical MRI <span class="hlt">acoustic</span> <span class="hlt">noise</span>, often substantially exceeding 100 dB, causes patient anxiety and discomfort and interferes with functional MRI (fMRI) and interventional MRI. MRI <span class="hlt">acoustic</span> <span class="hlt">noise</span> reduction is a long-standing and difficult technical challenge. The <span class="hlt">noise</span> is basically caused by large Lorentz forces on gradient windings--surrounding the patient bore--situated in strong magnetic fields (1.5 T, 3 T or higher). Pulsed currents of 300 A or more are switched through the gradient windings in sub-milliseconds. Experimenting with hardware <span class="hlt">noise</span> reduction on clinical scanners is difficult and expensive because of the large scale and weight of clinical scanner components (gradient windings ~ 1000 kg) that require special handling equipment in large engineering test facilities. Our approach is to produce a Truly Quiet (<70 dB) small-scale animal imager. Results serve as a test platform for <span class="hlt">acoustic</span> <span class="hlt">noise</span> reduction measures that can be implemented in clinical scanners. We have so far decreased <span class="hlt">noise</span> in an animal scale imager from 108 dB to 71 dB, a 37 dB reduction. Our <span class="hlt">noise</span> reduction measures include: a gradient container that can be evacuated; inflatable antivibration mounts to prevent transmission of vibrations from gradient winding to gradient container; vibration damping of wires going from gradient to the outside world via the gradient container; and a copper passive shield to prevent the generation of eddy currents in the metal cryostat inner bore, which in turn can vibrate and produce <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013SPIE.8711E..09R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013SPIE.8711E..09R"><span>A multi-band spectral subtraction-based algorithm for real-time <span class="hlt">noise</span> cancellation applied to gunshot <span class="hlt">acoustics</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ramos, António L. L.; Holm, Sverre; Gudvangen, Sigmund; Otterlei, Ragnvald</p> <p>2013-06-01</p> <p><span class="hlt">Acoustical</span> sniper positioning is based on the detection and direction-of-arrival estimation of the shockwave and the muzzle blast <span class="hlt">acoustical</span> signals. In real-life situations, the detection and direction-of-arrival estimation processes is usually performed under the influence of background <span class="hlt">noise</span> sources, e.g., vehicles <span class="hlt">noise</span>, and might result in non-negligible inaccuracies than can affect the system performance and reliability negatively, specially when detecting the muzzle sound under long range distance and absorbing terrains. This paper introduces a multi-band spectral subtraction based algorithm for real-time <span class="hlt">noise</span> reduction, applied to gunshot <span class="hlt">acoustical</span> signals. The ballistic shockwave and the muzzle blast signals exhibit distinct frequency contents that are affected differently by additive <span class="hlt">noise</span>. In most real situations, the <span class="hlt">noise</span> component is colored and a multi-band spectral subtraction approach for <span class="hlt">noise</span> reduction contributes to reducing the presence of artifacts in denoised signals. The proposed algorithm is tested using a dataset generated by combining signals from real gunshots and real vehicle <span class="hlt">noise</span>. The <span class="hlt">noise</span> component was generated using a steel tracked military tank running on asphalt and includes, therefore, the sound from the vehicle engine, which varies slightly in frequency over time according to the engine's rpm, and the sound from the steel tracks as the vehicle moves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3411812','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3411812"><span>Vessel <span class="hlt">Noise</span> Affects Beaked Whale Behavior: Results of a Dedicated <span class="hlt">Acoustic</span> Response Study</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Pirotta, Enrico; Milor, Rachael; Quick, Nicola; Moretti, David; Di Marzio, Nancy; Tyack, Peter; Boyd, Ian; Hastie, Gordon</p> <p>2012-01-01</p> <p>Some beaked whale species are susceptible to the detrimental effects of anthropogenic <span class="hlt">noise</span>. Most studies have concentrated on the effects of military sonar, but other forms of <span class="hlt">acoustic</span> disturbance (e.g. shipping <span class="hlt">noise</span>) may disrupt behavior. An experiment involving the exposure of target whale groups to intense vessel-generated <span class="hlt">noise</span> tested how these exposures influenced the foraging behavior of Blainville’s beaked whales (Mesoplodon densirostris) in the Tongue of the Ocean (Bahamas). A military array of bottom-mounted hydrophones was used to measure the response based upon changes in the spatial and temporal pattern of vocalizations. The archived <span class="hlt">acoustic</span> data were used to compute metrics of the echolocation-based foraging behavior for 16 targeted groups, 10 groups further away on the range, and 26 non-exposed groups. The duration of foraging bouts was not significantly affected by the exposure. Changes in the hydrophone over which the group was most frequently detected occurred as the animals moved around within a foraging bout, and their number was significantly less the closer the whales were to the sound source. Non-exposed groups also had significantly more changes in the primary hydrophone than exposed groups irrespective of distance. Our results suggested that broadband ship <span class="hlt">noise</span> caused a significant change in beaked whale behavior up to at least 5.2 kilometers away from the vessel. The observed change could potentially correspond to a restriction in the movement of groups, a period of more directional travel, a reduction in the number of individuals clicking within the group, or a response to changes in prey movement. PMID:22880022</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22880022','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22880022"><span>Vessel <span class="hlt">noise</span> affects beaked whale behavior: results of a dedicated <span class="hlt">acoustic</span> response study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pirotta, Enrico; Milor, Rachael; Quick, Nicola; Moretti, David; Di Marzio, Nancy; Tyack, Peter; Boyd, Ian; Hastie, Gordon</p> <p>2012-01-01</p> <p>Some beaked whale species are susceptible to the detrimental effects of anthropogenic <span class="hlt">noise</span>. Most studies have concentrated on the effects of military sonar, but other forms of <span class="hlt">acoustic</span> disturbance (e.g. shipping <span class="hlt">noise</span>) may disrupt behavior. An experiment involving the exposure of target whale groups to intense vessel-generated <span class="hlt">noise</span> tested how these exposures influenced the foraging behavior of Blainville's beaked whales (Mesoplodon densirostris) in the Tongue of the Ocean (Bahamas). A military array of bottom-mounted hydrophones was used to measure the response based upon changes in the spatial and temporal pattern of vocalizations. The archived <span class="hlt">acoustic</span> data were used to compute metrics of the echolocation-based foraging behavior for 16 targeted groups, 10 groups further away on the range, and 26 non-exposed groups. The duration of foraging bouts was not significantly affected by the exposure. Changes in the hydrophone over which the group was most frequently detected occurred as the animals moved around within a foraging bout, and their number was significantly less the closer the whales were to the sound source. Non-exposed groups also had significantly more changes in the primary hydrophone than exposed groups irrespective of distance. Our results suggested that broadband ship <span class="hlt">noise</span> caused a significant change in beaked whale behavior up to at least 5.2 kilometers away from the vessel. The observed change could potentially correspond to a restriction in the movement of groups, a period of more directional travel, a reduction in the number of individuals clicking within the group, or a response to changes in prey movement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940009563','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940009563"><span><span class="hlt">Noise</span> <span class="hlt">levels</span> from a model turbofan engine with simulated <span class="hlt">noise</span> control measures applied</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hall, David G.; Woodward, Richard P.</p> <p>1993-01-01</p> <p>A study of estimated full-scale <span class="hlt">noise</span> <span class="hlt">levels</span> based on measured <span class="hlt">levels</span> from the Advanced Ducted Propeller (ADP) sub-scale model is presented. Testing of this model was performed in the NASA Lewis Low Speed Anechoic Wind Tunnel at a simulated takeoff condition of Mach 0.2. Effective Perceived <span class="hlt">Noise</span> <span class="hlt">Level</span> (EPNL) estimates for the baseline configuration are documented, and also used as the control case in a study of the potential benefits of two categories of <span class="hlt">noise</span> control. The effect of active <span class="hlt">noise</span> control is evaluated by artificially removing various rotor-stator interaction tones. Passive <span class="hlt">noise</span> control is simulated by applying a notch filter to the wind tunnel data. Cases with both techniques are included to evaluate hybrid active-passive <span class="hlt">noise</span> control. The results for EPNL values are approximate because the original source data was limited in bandwidth and in sideline angular coverage. The main emphasis is on comparisons between the baseline and configurations with simulated <span class="hlt">noise</span> control measures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25360877','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25360877"><span>Induction of enhanced <span class="hlt">acoustic</span> startle response by <span class="hlt">noise</span> exposure: dependence on exposure conditions and testing parameters and possible relevance to hyperacusis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Salloum, Rony H; Yurosko, Christopher; Santiago, Lia; Sandridge, Sharon A; Kaltenbach, James A</p> <p>2014-01-01</p> <p>There has been a recent surge of interest in the development of animal models of hyperacusis, a condition in which tolerance to sounds of moderate and high intensities is diminished. The reasons for this decreased tolerance are likely multifactorial, but some major factors that contribute to hyperacusis are increased loudness perception and heightened sensitivity and/or responsiveness to sound. Increased sound sensitivity is a symptom that sometimes develops in human subjects after <span class="hlt">acoustic</span> insult and has recently been demonstrated in animals as evidenced by enhancement of the <span class="hlt">acoustic</span> startle reflex following <span class="hlt">acoustic</span> over-exposure. However, different laboratories have obtained conflicting results in this regard, with some studies reporting enhanced startle, others reporting weakened startle, and still others reporting little, if any, change in the amplitude of the <span class="hlt">acoustic</span> startle reflex following <span class="hlt">noise</span> exposure. In an effort to gain insight into these discrepancies, we conducted measures of <span class="hlt">acoustic</span> startle responses (ASR) in animals exposed to different <span class="hlt">levels</span> of sound, and repeated such measures on consecutive days using a range of different startle stimuli. Since many studies combine measures of <span class="hlt">acoustic</span> startle with measures of gap detection, we also tested ASR in two different <span class="hlt">acoustic</span> contexts, one in which the startle amplitudes were tested in isolation, the other in which startle amplitudes were measured in the context of the gap detection test. The results reveal that the emergence of chronic hyperacusis-like enhancements of startle following <span class="hlt">noise</span> exposure is highly reproducible but is dependent on the post-exposure thresholds, the time when the measures are performed and the context in which the ASR measures are obtained. These findings could explain many of the discrepancies that exist across studies and suggest guidelines for inducing in animals enhancements of the startle reflex that may be related to hyperacusis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003ASAJ..114.2365L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003ASAJ..114.2365L"><span>A note on the <span class="hlt">acoustic</span>-phonetic characteristics of non-native English vowels produced in <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Chi-Nin; Munro, Murray J.</p> <p>2003-10-01</p> <p>The Lombard reflex occurs when people unconsciously raise their vocal <span class="hlt">levels</span> in the presence of loud background <span class="hlt">noise</span>. Previous work has established that utterances produced in noisy environments exhibit increases in vowel duration and fundamental frequency (F0), and a shift in formant center frequencies for F1 and F2. Most studies of the Lombard reflex have been conducted with native speakers; research with second-language speakers is much less common. The present study examined the effects of the Lombard reflex on foreign-accented English vowel productions. Seven female Cantonese speakers and a comparison group of English speakers were recorded producing three vowels (/i u a/) in /bVt/ context in quiet and in 70 dB of masking <span class="hlt">noise</span>. Vowel durations, F0, and the first two formants for each of the three vowels were measured. Analyses revealed that vowel durations and F0 were greater in the vowels produced in <span class="hlt">noise</span> than those produced in quiet in most cases. First formants, but not F2, were consistently higher in Lombard speech than in normal speech. The findings suggest that non-native English speakers exhibit <span class="hlt">acoustic</span>-phonetic patterns similar to those of native speakers when producing English vowels in noisy conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750019994','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750019994"><span>Interior <span class="hlt">noise</span> <span class="hlt">levels</span> of two propeller-driven light aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Catherines, J. J.; Mayes, W. H.</p> <p>1975-01-01</p> <p>The relationships between aircraft operating conditions and interior <span class="hlt">noise</span> and the degree to which ground testing can be used in lieu of flight testing for performing interior <span class="hlt">noise</span> research were studied. The results show that the <span class="hlt">noise</span> inside light aircraft is strongly influenced by the rotational speed of the engine and propeller. Both the overall <span class="hlt">noise</span> and low frequency spectra <span class="hlt">levels</span> were observed to decrease with increasing high speed rpm operations during flight. This phenomenon and its significance is not presently understood. Comparison of spectra obtained in flight with spectra obtained on the ground suggests that identification of frequency components and relative amplitude of propeller and engine <span class="hlt">noise</span> sources may be evaluated on stationary aircraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800051329&hterms=wind+turbine+impact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dwind%2Bturbine%2Bimpact','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800051329&hterms=wind+turbine+impact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dwind%2Bturbine%2Bimpact"><span>An exploratory survey of <span class="hlt">noise</span> <span class="hlt">levels</span> associated with a 100 kW wind turbine</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Balombin, J. R.</p> <p>1980-01-01</p> <p>During performance tests of a 125-foot diameter, 100 kW wind turbine at the NASA Plum Brook Station near Sandusky, Ohio, the opportunity arose to make exploratory <span class="hlt">noise</span> measurements and results of those surveys are presented. The data include measurements as functions of distance from the turbine, and directivity angle, and cover a frequency range from 1 Hz to several kHz. Potential community impact is discussed in terms of A-weighted <span class="hlt">noise</span> <span class="hlt">levels</span> relative to background <span class="hlt">levels</span>, and the infrasonic spectral content. Finally, the change in the sound power spectrum associated with a change in the rotor speed is described. The <span class="hlt">acoustic</span> impact of this size wind turbine is judged to be minimal.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050196669','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050196669"><span>Validation of the Small Hot Jet <span class="hlt">Acoustic</span> Rig for Jet <span class="hlt">Noise</span> Research</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bridges, James; Brown, Clifford A.</p> <p>2005-01-01</p> <p>The development and <span class="hlt">acoustic</span> validation of the Small Hot Jet Aeroacoustic Rig (SHJAR) is documented. Originally conceived to support fundamental research in jet <span class="hlt">noise</span>, the rig has been designed and developed using the best practices of the industry. While validating the rig for <span class="hlt">acoustic</span> work, a method of characterizing all extraneous rig <span class="hlt">noise</span> was developed. With this in hand, the researcher can know when the jet data being measured is being contaminated and design the experiment around this limitation. Also considered is the question of uncertainty, where it is shown that there is a fundamental uncertainty of 0.5dB or so to the best experiments, confirmed by repeatability studies. One area not generally accounted for in the uncertainty analysis is the variation which can result from differences in initial condition of the nozzle shear layer. This initial condition was modified and the differences in both flow and sound were documented. The bottom line is that extreme caution must be applied when working on small jet rigs, but that highly accurate results can be made independent of scale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007APS..DFD.GH004M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007APS..DFD.GH004M"><span>Prediction of the <span class="hlt">noise</span> of flow over a cylinder by direct computation and <span class="hlt">acoustic</span> analogy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mani, Ali; Wang, Meng; Moin, Parviz</p> <p>2007-11-01</p> <p>The sound field of flow over a circular cylinder at ReD=3900 and Ma=0.4 is evaluated using Large-Eddy Simulation (LES). The <span class="hlt">acoustic</span> results computed directly from LES are compared with those obtained using an integral solution of the Ffowcs Williams-Hawkings (FW-H) equation in conjunction with the LES source field data. The modified FW-H solution is derived using a free-space Green function which accounts for the uniform mean flow and spanwise periodicity in the flow simulation. In the implementation of the FW-H solution, the cylinder surface and three porous surfaces with different distances from the cylinder are used as integration surfaces. The effect of turbulent flow structures crossing the integration boundary on the generation of artificial <span class="hlt">noise</span> is studied. The quadrupole terms in the FW-H equation are found to be important in canceling artificial <span class="hlt">noise</span> regardless of their physical significance. Alternative formulations of <span class="hlt">acoustic</span> analogy that can better handle the boundary terms will be discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSV...333..761G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSV...333..761G"><span><span class="hlt">Acoustical</span> inverse problems regularization: Direct definition of filter factors using Signal-to-<span class="hlt">Noise</span> Ratio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gauthier, P.-A.; Gérard, A.; Camier, C.; Berry, A.</p> <p>2014-02-01</p> <p><span class="hlt">Acoustic</span> imaging aims at localization and characterization of sound sources using microphone arrays. In this paper a new regularization method for <span class="hlt">acoustic</span> imaging by inverse approach is proposed. The method first relies on the singular value decomposition of the plant matrix and on the projection of the measured data on the corresponding singular vectors. In place of regularization using classical methods such as truncated singular value decomposition and Tikhonov regularization, the proposed method involves the direct definition of the filter factors on the basis of a thresholding operation, defined from the estimated measurement <span class="hlt">noise</span>. The thresholding operation is achieved using modified filter functions. The originality of the approach is to propose the definition of a filter factor which provides more damping to the singular components dominated by <span class="hlt">noise</span> than that given by the Tikhonov filter. This has the advantage of potentially simplifying the selection of the best regularization amount in inverse problems. Theoretical results show that this method is comparatively more accurate than Tikhonov regularization and truncated singular value decomposition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130000430','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130000430"><span>Advanced Jet <span class="hlt">Noise</span> Exhaust Concepts in NASA's N+2 Supersonics Validation Study and the Environmentally Responsible Aviation Project's Upcoming Hybrid Wing Body <span class="hlt">Acoustics</span> Test</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Henderson, Brenda S.; Doty, Mike</p> <p>2012-01-01</p> <p><span class="hlt">Acoustic</span> and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-<span class="hlt">Acoustic</span> Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts presented here utilized lobed-mixers and ejectors. A powered third-stream was implemented to improve ejector <span class="hlt">acoustic</span> performance. One concept was found to produce stagnant flow within the ejector and the other produced discrete-frequency tones (due to flow separations within the model) that degraded the <span class="hlt">acoustic</span> performance of the exhaust concept. NASA's Environmentally Responsible Aviation (ERA) Project has been investigating a Hybrid Wing Body (HWB) aircraft as a possible configuration for meeting N+2 system <span class="hlt">level</span> goals for <span class="hlt">noise</span>, emissions, and fuel burn. A recently completed NRA led by Boeing Research and Technology resulted in a full-scale aircraft design and wind tunnel model. This model will be tested <span class="hlt">acoustically</span> in NASA Langley's 14-by 22-Foot Subsonic Tunnel and will include dual jet engine simulators and broadband engine <span class="hlt">noise</span> simulators as part of the test campaign. The objectives of the test are to characterize the system <span class="hlt">level</span> <span class="hlt">noise</span>, quantify the effects of shielding, and generate a valuable database for prediction method development. Further details of the test and various component preparations are described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880009834','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880009834"><span><span class="hlt">Acoustic</span> measurements from a rotor blade-vortex interaction <span class="hlt">noise</span> experiment in the German-Dutch Wind Tunnel (DNW)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Martin, Ruth M.; Splettstoesser, W. R.; Elliott, J. W.; Schultz, K.-J.</p> <p>1988-01-01</p> <p><span class="hlt">Acoustic</span> data are presented from a 40 percent scale model of the 4-bladed BO-105 helicopter main rotor, measured in the large European aeroacoustic wind tunnel, the DNW. Rotor blade-vortex interaction (BVI) <span class="hlt">noise</span> data in the low speed flight range were acquired using a traversing in-flow microphone array. The experimental apparatus, testing procedures, calibration results, and experimental objectives are fully described. A large representative set of averaged <span class="hlt">acoustic</span> signals is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA531686','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA531686"><span>Emergence of the Green’s Functions from <span class="hlt">Noise</span> and Passive <span class="hlt">Acoustic</span> Remote Sensing of Ocean Dynamics</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2009-09-30</p> <p><span class="hlt">Acoustic</span> Remote Sensing of Ocean Dynamics Oleg A. Godin CIRES/Univ. of Colorado and NOAA/OAR/Earth System Research Lab., R/PSD99, 325 Broadway...characterization of a time-varying ocean where ambient <span class="hlt">acoustic</span> <span class="hlt">noise</span> is utilized as a probing signal. • To develop a passive remote sensing technique for...inapplicable. 3. To quantify degradation of performance of passive remote sensing techniques due to ocean surface motion and other variations of underwater</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1770c0120F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1770c0120F"><span>Numerical simulation of the processes in the normal incidence tube for high <span class="hlt">acoustic</span> pressure <span class="hlt">levels</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fedotov, E. S.; Khramtsov, I. V.; Kustov, O. Yu.</p> <p>2016-10-01</p> <p>Numerical simulation of the <span class="hlt">acoustic</span> processes in an impedance tube at high <span class="hlt">levels</span> of <span class="hlt">acoustic</span> pressure is a way to solve a problem of <span class="hlt">noise</span> suppressing by liners. These studies used liner specimen that is one cylindrical Helmholtz resonator. The evaluation of the real and imaginary parts of the liner <span class="hlt">acoustic</span> impedance and sound absorption coefficient was performed for sound pressure <span class="hlt">levels</span> of 130, 140 and 150 dB. The numerical simulation used experimental data having been obtained on the impedance tube with normal incidence waves. At the first stage of the numerical simulation it was used the linearized Navier-Stokes equations, which describe well the imaginary part of the liner impedance whatever the sound pressure <span class="hlt">level</span>. These equations were solved by finite element method in COMSOL Multiphysics program in axisymmetric formulation. At the second stage, the complete Navier-Stokes equations were solved by direct numerical simulation in ANSYS CFX in axisymmetric formulation. As the result, the acceptable agreement between numerical simulation and experiment was obtained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110011393','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110011393"><span>Core <span class="hlt">Noise</span>: Implications of Emerging N+3 Designs and <span class="hlt">Acoustic</span> Technology Needs</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hultgren, Lennart S.</p> <p>2011-01-01</p> <p>This presentation is a summary of the core-<span class="hlt">noise</span> implications of NASA's primary N+3 aircraft concepts. These concepts are the MIT/P&W D8.5 Double Bubble design, the Boeing/GE SUGAR Volt hybrid gas-turbine/electric engine concept, the NASA N3-X Turboelectric Distributed Propulsion aircraft, and the NASA TBW-XN Truss-Braced Wing concept. The first two are future concepts for the Boeing 737/Airbus A320 US transcontinental mission of 180 passengers and a maximum range of 3000 nm. The last two are future concepts for the Boeing 777 transpacific mission of 350 passengers and a 7500 nm range. Sections of the presentation cover: turbofan design trends on the N+1.5 time frame and the already emerging importance of core <span class="hlt">noise</span>; the NASA N+3 concepts and associated core-<span class="hlt">noise</span> challenges; the historical trends for the engine bypass ratio (BPR), overall pressure ratio (OPR), and combustor exit temperature; and brief discussion of a <span class="hlt">noise</span> research roadmap being developed to address the core-<span class="hlt">noise</span> challenges identified for the N+3 concepts. The N+3 conceptual aircraft have (i) ultra-high bypass ratios, in the rage of 18 - 30, accomplished by either having a small-size, high-power-density core, an hybrid design which allows for an increased fan size, or by utilizing a turboelectric distributed propulsion design; and (ii) very high OPR in the 50 - 70 range. These trends will elevate the overall importance of turbomachinery core <span class="hlt">noise</span>. The N+3 conceptual designs specify the need for the development and application of advanced liners and passive and active control strategies to reduce the core <span class="hlt">noise</span>. Current engineering prediction of core <span class="hlt">noise</span> uses semi-empirical methods based on older turbofan engines, with (at best) updates for more recent designs. The models have not seen the same <span class="hlt">level</span> of development and maturity as those for fan and jet <span class="hlt">noise</span> and are grossly inadequate for the designs considered for the N+3 time frame. An aggressive program for the development of updated <span class="hlt">noise</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3891787','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3891787"><span>Pilot task-based assessment of <span class="hlt">noise</span> <span class="hlt">levels</span> among firefighters</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Neitzel, RL; Hong, O; Quinlan, P; Hulea, R</p> <p>2012-01-01</p> <p>PURPOSE Over one million American firefighters are routinely exposed to various occupational hazards agents. While efforts have been made to identify and reduce some causes of injuries and illnesses among firefighters, relatively little has been done to evaluate and understand occupational <span class="hlt">noise</span> exposures in this group. The purpose of this pilot study was to apply a task-based <span class="hlt">noise</span> exposure assessment methodology to firefighting operations to evaluate potential <span class="hlt">noise</span> exposure sources, and to use collected task-based <span class="hlt">noise</span> <span class="hlt">levels</span> to create <span class="hlt">noise</span> exposure estimates for evaluation of risk of <span class="hlt">noise</span>-induced hearing loss by comparison to the 8-hr and 24-hr recommended exposure limits (RELs) for <span class="hlt">noise</span> of 85 and 80.3 dBA, respectively. METHODS Task-based <span class="hlt">noise</span> exposures (n=100 measurements) were measured in three different fire departments (a rural department in Southeast Michigan and suburban and urban departments in Northern California). These <span class="hlt">levels</span> were then combined with time-at-task information collected from firefighters to estimate 8-hr <span class="hlt">noise</span> exposures for the rural and suburban fire departments (n=6 estimates for each department). Data from 24-hr dosimetry measurements and crude self-reported activity categories from the urban fire department (n=4 measurements) were used to create 24-hr exposure estimates to evaluate the bias associated with the task-based estimates. RESULTS Task-based <span class="hlt">noise</span> <span class="hlt">levels</span> were found to range from 82–109 dBA, with the highest <span class="hlt">levels</span> resulting from use of saws and pneumatic chisels. Some short (e.g., 30 min) sequences of common tasks were found to result in nearly an entire allowable daily exposure. The majority of estimated 8-hr and 24-hr exposures exceeded the relevant recommended exposure limit. Predicted 24-hr exposures showed substantial imprecision in some cases, suggesting the need for increased task specificity. CONCLUSIONS The results indicate potential for overexposure to <span class="hlt">noise</span> from a variety of firefighting tasks and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1013168','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1013168"><span>Factors Affecting <span class="hlt">Noise</span> <span class="hlt">Levels</span> of High-Speed Handpieces</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2012-06-01</p> <p>office communication and increase patient anxiety. Purpose: To determine if three <span class="hlt">noise</span>-reducing techniques utilized in larger scale , non- dental...hearing loss may cause confusion, fear, and loneliness , and that sometimes hearing loss is accompanied by dizziness, which would be a handicap in the...employee <span class="hlt">noise</span> exposures equal or exceed an 8- hour time-weighted average sound <span class="hlt">level</span> (TWA) of 85 decibels measured on the A scale (slow response) or</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002APS..MARG29005V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002APS..MARG29005V"><span>Networking with <span class="hlt">noise</span> at the molecular, cellular, and population <span class="hlt">level</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vilar, Jose</p> <p>2002-03-01</p> <p>The intrinsic stochastic nature of biochemical reactions affects enzymatic and transcriptional networks at different <span class="hlt">levels</span>. Yet, cells are able to function effectively and consistently amidst such random fluctuations. I will discuss some molecular mechanisms that are able to reduce the intrinsic <span class="hlt">noise</span> of chemical reactions, how suitable designs can make networks resistant to <span class="hlt">noise</span>, and what strategies can be used by populations to achieve precise functions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/8458743','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/8458743"><span>The intensitive DL of tones: dependence of signal/masker ratio on tone <span class="hlt">level</span> and on spectrum of added <span class="hlt">noise</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Greenwood, D D</p> <p>1993-02-01</p> <p>In Greenwood [J. <span class="hlt">Acoust</span>. Soc. Am. 33, 484-502 (1961a)] the ratio of masked signal threshold to masker <span class="hlt">level</span> (S/M) decreased about 4 dB at a masker <span class="hlt">level</span> of about 50 dB SL, the 'transition' <span class="hlt">level</span>, when <span class="hlt">noise</span> bands were subcritical but not when supercritical. Schlauch et al. [J. <span class="hlt">Acoust</span>. Soc. Am. 71, S73 (1982)] report a related result. A pilot study [Greenwood, Harvard Psychoacoustic Lab. Status Report 37, 8-9 (1961)] in which pure tones masked identical tones in-phase showed a larger change in S/M. Detailed tone-tone growth-of-masking curves from over a dozen subjects in 1967-69, and in 1960, are reported here. A transition in slope, of variable abruptness, often begins to occur at about 50 dB SL, dropping S/M ratio by 6 to 8 dB or more [Rabinowitz et al., J. <span class="hlt">Acoust</span>. Soc. Am. 35, 1053 (1976)]; the curves sometimes possess two segments, sometimes are simply convex. All have overall slopes less than 1.0, known also as the 'near miss'. Consistent with other results [Zwicker, Acustica 6, 365-396 (1956); Viemeister, J. <span class="hlt">Acoust</span>. Soc. Am. 51, 1265-1296 (1972); Moore and Raab, J. <span class="hlt">Acoust</span>. Soc. Am. 55, 1049-1060 (1974)], addition of low-<span class="hlt">level</span> wide-band and high-pass <span class="hlt">noise</span> was found to counteract the change in S/M, i.e., to raise the high-<span class="hlt">level</span> section of the growth-of-masking curve. However, the ability of narrow 'band-pass' <span class="hlt">noise</span> to exert this effect was greatest when added at a frequency ratio (band/masking-tone) of 1.3 to 1.5, which seems more closely to link the effects of added <span class="hlt">noise</span> to the effects of increasing a masking band from sub- to supercritical width (above). Interpretation of the decrease in DL with <span class="hlt">level</span> begins by noting that the 'transition' <span class="hlt">level</span> correlates approximately with the <span class="hlt">level</span> at which a primary unit population excited by a given pure tone begins rapidly to expand basally. Underlying this, the basalward shift of a tone's displacement envelope peak accelerates at about the same <span class="hlt">level</span> [Rhode, J. <span class="hlt">Acoust</span>. Soc. Am. 49, 1218-1231 (1971); Sellick et al., J</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA517254','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA517254"><span>High Frequency <span class="hlt">Acoustic</span> Propagation using <span class="hlt">Level</span> Set Methods</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2007-01-01</p> <p>solution of the high frequency approximation to the wave equation. Traditional solutions to the Eikonal equation in high frequency <span class="hlt">acoustics</span> are...curvature can be extracted at any point of the front from the <span class="hlt">level</span> set function (provided the normal and curvature are well-defined at that point ), and... points per wavelength to resolve the wave). Ray tracing is therefore the current standard for high frequency propagation modeling. LSM may provide</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740018137','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740018137"><span>Advanced supersonic propulsion study. [with emphasis on <span class="hlt">noise</span> <span class="hlt">level</span> reduction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sabatella, J. A. (Editor)</p> <p>1974-01-01</p> <p>A study was conducted to determine the promising propulsion systems for advanced supersonic transport application, and to identify the critical propulsion technology requirements. It is shown that <span class="hlt">noise</span> constraints have a major effect on the selection of the various engine types and cycle parameters. Several promising advanced propulsion systems were identified which show the potential of achieving lower <span class="hlt">levels</span> of sideline jet <span class="hlt">noise</span> than the first generation supersonic transport systems. The non-afterburning turbojet engine, utilizing a very high <span class="hlt">level</span> of jet suppression, shows the potential to achieve FAR 36 <span class="hlt">noise</span> <span class="hlt">level</span>. The duct-heating turbofan with a low <span class="hlt">level</span> of jet suppression is the most attractive engine for <span class="hlt">noise</span> <span class="hlt">levels</span> from FAR 36 to FAR 36 minus 5 EPNdb, and some series/parallel variable cycle engines show the potential of achieving <span class="hlt">noise</span> <span class="hlt">levels</span> down to FAR 36 minus 10 EPNdb with moderate additional penalty. The study also shows that an advanced supersonic commercial transport would benefit appreciably from advanced propulsion technology. The critical propulsion technology needed for a viable supersonic propulsion system, and the required specific propulsion technology programs are outlined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780016954','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780016954"><span><span class="hlt">Acoustic</span> evaluation of a novel swept-rotor fan. [<span class="hlt">noise</span> reduction in turbofan engines</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lucas, J. G.; Woodward, R. P.; Mackinnon, M. J.</p> <p>1978-01-01</p> <p>Inlet <span class="hlt">noise</span> and aerodynamic performance are presented for a high tip speed fan designed with rotor blade leading edge sweep that gives a subsonic component of inlet Mach number normal to the edge at all radii. The intent of the design was to minimize the generation of rotor leading edge shock waves thereby minimizing multiple pure tone <span class="hlt">noise</span>. Sound power <span class="hlt">level</span> and spectral comparisons are made with several high-speed fans of conventional design. Results show multiple pure tone <span class="hlt">noise</span> at <span class="hlt">levels</span> below those of some of the other fans and this <span class="hlt">noise</span> was initiated at a higher tip speed. Aerodynamic performance of the fan did not meet design goals for this first build which applied conventional design procedures to the swept fan geometry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22350927','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22350927"><span>Observation of the fundamental Nyquist <span class="hlt">noise</span> limit in an ultra-high Q-factor cryogenic bulk <span class="hlt">acoustic</span> wave cavity</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Goryachev, Maxim Ivanov, Eugene N.; Tobar, Michael E.; Kann, Frank van; Galliou, Serge</p> <p>2014-10-13</p> <p>Thermal Nyquist <span class="hlt">noise</span> fluctuations of high-Q bulk <span class="hlt">acoustic</span> wave cavities have been observed at cryogenic temperatures with a DC superconducting quantum interference device amplifier. High Q modes with bandwidths of few tens of milliHz produce thermal fluctuations with a signal-to-<span class="hlt">noise</span> ratio of up to 23 dB. The estimated effective temperature from the Nyquist <span class="hlt">noise</span> is in good agreement with the physical temperature of the device, confirming the validity of the equivalent circuit model and the non-existence of any excess resonator self-<span class="hlt">noise</span>. The measurements also confirm that the quality factor remains extremely high (Q > 10{sup 8} at low order overtones) for very weak (thermal) system motion at low temperatures, when compared to values measured with relatively strong external excitation. This result represents an enabling step towards operating such a high-Q <span class="hlt">acoustic</span> device at the standard quantum limit.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=noise+AND+environment&pg=2&id=EJ721822','ERIC'); return false;" href="http://eric.ed.gov/?q=noise+AND+environment&pg=2&id=EJ721822"><span><span class="hlt">Noise</span> <span class="hlt">Levels</span> in Hong Kong Primary Schools: Implications for Classroom Listening</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Choi, Ching Yee; McPherson, Bradley</p> <p>2005-01-01</p> <p>Many researchers have stressed that the <span class="hlt">acoustic</span> environment is crucial to the speech perception, academic performance, attention, and participation of students in classrooms. Classrooms in highly urbanised locations are especially vulnerable to <span class="hlt">noise</span>, a major influence on the <span class="hlt">acoustic</span> environment. The purpose of this investigation was to…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970028883','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970028883"><span>Confusion <span class="hlt">Noise</span> <span class="hlt">Level</span> Due to Galactic and Extragalactic Binaries</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bender, Peter L.; Hils, Dieter</p> <p>1997-01-01</p> <p>We have revised our earlier rough estimate of the combined galactic and extragalactic binary confusion <span class="hlt">noise</span> <span class="hlt">level</span> curve for gravitational waves. This was done to correct some numerical errors and to allow for roughly three frequency bins worth of information about weaker sources being lost for each galactic binary signal that is removed from the data. The results are still based on the spectral amplitude estimates for different types of galactic binaries reported by Hils et al in 1990, and assume that the gravitational wave power spectral densities for other galaxies are proportional to the optical luminosities. The estimated confusion <span class="hlt">noise</span> <span class="hlt">level</span> drops to the LISA instrumental <span class="hlt">noise</span> <span class="hlt">level</span> at between roughly 3 and 8 MHz.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11303918','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11303918"><span>Simulation of jet-<span class="hlt">noise</span> excitation in an <span class="hlt">acoustic</span> progressive wave tube facility.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Steinwolf, A; White, R G; Wolfe, H F</p> <p>2001-03-01</p> <p><span class="hlt">Acoustic</span> excitation produced by jet-engine effluxes was simulated in a progressive wave tube (APWT) facility with a computer-based control system. The APWT siren is driven by a signal generated numerically in a PC and then converted into analog form. Characteristics of the <span class="hlt">acoustic</span> pressure measured by a microphone are analyzed in digital form and compared with those prescribed for simulation. Divergence is compensated by immediate modification of the driving signal and this action is repeated in the form of iterative process until the test specification is attained. Typical power spectral density (PSD) shapes with maxima at low and high frequencies were simulated. A "tailoring" approach has been also achieved when a test specification was determined directly from field measurements for the particular aircraft under consideration. Since <span class="hlt">acoustic</span> pressure signals of high <span class="hlt">level</span> differ from the Gaussian random process model, particularly in terms of asymmetric probability density function, a method has been developed to make the driving signal also non-Gaussian by simulating skewness and kurtosis parameters of the APWT <span class="hlt">acoustic</span> excitation simultaneously with PSD control. Experimental results with Gaussian and non-Gaussian characteristics obtained for various PSD specifications including sharp and narrow peaks are presented in the paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27654323','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27654323"><span>Spatial Prediction Filtering of <span class="hlt">Acoustic</span> Clutter and Random <span class="hlt">Noise</span> in Medical Ultrasound Imaging.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Shin, Junseob; Huang, Lianjie</p> <p>2017-02-01</p> <p>One of the major challenges in array-based medical ultrasound imaging is the image quality degradation caused by sidelobes and off-axis clutter, which is an inherent limitation of the conventional delay-and-sum (DAS) beamforming operating on a finite aperture. Ultrasound image quality is further degraded in imaging applications involving strong tissue attenuation and/or low transmit power. In order to effectively suppress <span class="hlt">acoustic</span> clutter from off-axis targets and random <span class="hlt">noise</span> in a robust manner, we introduce in this paper a new adaptive filtering technique called frequency-space (F-X) prediction filtering or FXPF, which was first developed in seismic imaging for random <span class="hlt">noise</span> attenuation. Seismologists developed FXPF based on the fact that linear and quasilinear events or wavefronts in the time-space (T-X) domain are manifested as a superposition of harmonics in the frequency-space (F-X) domain, which can be predicted using an auto-regressive (AR) model. We describe the FXPF technique as a spectral estimation or a direction-of-arrival problem, and explain why adaptation of this technique into medical ultrasound imaging is beneficial. We apply our new technique to simulated and tissue-mimicking phantom data. Our results demonstrate that FXPF achieves CNR improvements of 26% in simulated <span class="hlt">noise</span>-free anechoic cyst, 109% in simulated anechoic cyst contaminated with random <span class="hlt">noise</span> of 15 dB SNR, and 93% for experimental anechoic cyst from a custom-made tissue-mimicking phantom. Our findings suggest that FXPF is an effective technique to enhance ultrasound image contrast and has potential to improve the visualization of clinically important anatomical structures and diagnosis of diseased conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27563964','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27563964"><span>Preparation of Ultracold Atom Clouds at the Shot <span class="hlt">Noise</span> <span class="hlt">Level</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gajdacz, M; Hilliard, A J; Kristensen, M A; Pedersen, P L; Klempt, C; Arlt, J J; Sherson, J F</p> <p>2016-08-12</p> <p>We prepare number stabilized ultracold atom clouds through the real-time analysis of nondestructive images and the application of feedback. In our experiments, the atom number N∼10^{6} is determined by high precision Faraday imaging with uncertainty ΔN below the shot <span class="hlt">noise</span> <span class="hlt">level</span>, i.e., ΔN<sqrt[N]. Based on this measurement, feedback is applied to reduce the atom number to a user-defined target, whereupon a second imaging series probes the number stabilized cloud. By this method, we show that the atom number in ultracold clouds can be prepared below the shot <span class="hlt">noise</span> <span class="hlt">level</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950005928','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950005928"><span>En route <span class="hlt">noise</span> <span class="hlt">levels</span> from propfan test assessment airplane</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Garber, Donald P.; Willshire, William L., Jr.</p> <p>1994-01-01</p> <p>The en route <span class="hlt">noise</span> test was designed to characterize propagation of propfan <span class="hlt">noise</span> from cruise altitudes to the ground. In-flight measurements of propfan source <span class="hlt">levels</span> and directional patterns were made by a chase plane flying in formation with the propfan test assessment (PTA) airplane. Ground <span class="hlt">noise</span> measurements were taken during repeated flights over a distributed microphone array. The microphone array on the ground was used to provide ensemble-averaged estimates of mean flyover <span class="hlt">noise</span> <span class="hlt">levels</span>, establish confidence limits for those means, and measure propagation-induced <span class="hlt">noise</span> variability. Even for identical nominal cruise conditions, peak sound <span class="hlt">levels</span> for individual overflights varied substantially about the average, particularly when overflights were performed on different days. Large day-to-day variations in peak <span class="hlt">level</span> measurements appeared to be caused by large day-to-day differences in propagation conditions and tended to obscure small variations arising from operating conditions. A parametric evaluation of the sensitivity of this prediction method to weather measurement and source <span class="hlt">level</span> uncertainties was also performed. In general, predictions showed good agreement with measurements. However, the method was unable to predict short-term variability of ensemble-averaged data within individual overflights. Although variations in absorption appear to be the dominant factor in variations of peak sound <span class="hlt">levels</span> recorded on the ground, accurate predictions of those <span class="hlt">levels</span> require that a complete description of operational conditions be taken into account. The comprehensive and integrated methods presented in this paper have adequately predicted ground-measured sound <span class="hlt">levels</span>. On average, peak sound <span class="hlt">levels</span> were predicted within 3 dB for each of the three different cruise conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18646974','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18646974"><span>Self-reported sleep disturbances due to railway <span class="hlt">noise</span>: exposure-response relationships for nighttime equivalent and maximum <span class="hlt">noise</span> <span class="hlt">levels</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Aasvang, Gunn Marit; Moum, Torbjorn; Engdahl, Bo</p> <p>2008-07-01</p> <p>The objective of the present survey was to study self-reported sleep disturbances due to railway <span class="hlt">noise</span> with respect to nighttime equivalent <span class="hlt">noise</span> <span class="hlt">level</span> (L(p,A,eq,night)) and maximum <span class="hlt">noise</span> <span class="hlt">level</span> (L(p,A,max)). A sample of 1349 people in and around Oslo in Norway exposed to railway <span class="hlt">noise</span> was studied in a cross-sectional survey to obtain data on sleep disturbances, sleep problems due to <span class="hlt">noise</span>, and personal characteristics including <span class="hlt">noise</span> sensitivity. Individual <span class="hlt">noise</span> exposure <span class="hlt">levels</span> were determined outside of the bedroom facade, the most-exposed facade, and inside the respondents' bedrooms. The exposure-response relationships were analyzed by using logistic regression models, controlling for possible modifying factors including the number of <span class="hlt">noise</span> events (train pass-by frequency). L(p,A,eq,night) and L(p,A,max) were significantly correlated, and the proportion of reported <span class="hlt">noise</span>-induced sleep problems increased as both L(p,A,eq,night) and L(p,A,max) increased. <span class="hlt">Noise</span> sensitivity, type of bedroom window, and pass-by frequency were significant factors affecting <span class="hlt">noise</span>-induced sleep disturbances, in addition to the <span class="hlt">noise</span> exposure <span class="hlt">level</span>. Because about half of the study population did not use a bedroom at the most-exposed side of the house, the exposure-response curve obtained by using <span class="hlt">noise</span> <span class="hlt">levels</span> for the most-exposed facade underestimated <span class="hlt">noise</span>-induced sleep disturbance for those who actually have their bedroom at the most-exposed facade.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=smith&pg=6&id=EJ986098','ERIC'); return false;" href="http://eric.ed.gov/?q=smith&pg=6&id=EJ986098"><span>What's All the <span class="hlt">Noise</span>? Differentiating Dimensions of <span class="hlt">Acoustic</span> Stress and the Limits to Meta-Analysis: Reply to Smith (2012)</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Szalma, J. L.; Hancock, P. A.</p> <p>2012-01-01</p> <p>Smith (2012) has provided pertinent observations on our recently published meta-analytic review (Szalma & Hancock, 2011) of the effects of <span class="hlt">acoustic</span> <span class="hlt">noise</span> on performance. His main points are as follows: (a) our review excluded some areas of research; (b) there were conceptual problems with our moderator analyses; and (c) limitations to…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA542098','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA542098"><span>Emergence of the Green’s Functions from <span class="hlt">Noise</span> and Passive <span class="hlt">Acoustic</span> Remote Sensing of Ocean Dynamics</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2010-09-30</p> <p>environments, Acta Acustica united with Acustica , 95, no. 6, p. 963–974 (2009b) [published, refereed] O. A. Godin, Emergence of deterministic Green’s...Godin, Emergence of <span class="hlt">acoustic</span> Green’s functions from time averages of ambient <span class="hlt">noise</span>, Acta Acustica united with Acustica (2010) [in press, refereed</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6973426','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6973426"><span><span class="hlt">Acoustic</span> <span class="hlt">noise</span> reduction for vehicle engines. (Latest citations from the US Patent Bibliographic file with exemplary claims). Published Search</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Not Available</p> <p>1994-06-01</p> <p>The bibliography contains citations of selected patents concerning methods, devices, and materials to reduce <span class="hlt">acoustic</span> <span class="hlt">noise</span> in vehicle engines. Vehicles covered include automobiles, railway locomotives, agricultural tractors, and aircraft. Internal combustion, diesel, and gas turbine engines are covered. (Contains a minimum of 188 citations and includes a subject term index and title list.)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ASAJ..118.1871K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ASAJ..118.1871K"><span><span class="hlt">Acoustical</span> and <span class="hlt">noise</span> redesign considerations when trying to increase patient privacy while ensuring comfort</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Klavetter, Eric</p> <p>2005-09-01</p> <p>An internal assessment was undertaken to understand the flow of patients to ensure comfort and privacy during their health care experience at Mayo Clinic. A number of different prototypes, work flows, and methodologies were utilized and assessed to determine the ``best experience for our patients.'' A number of prototypes ranging from self-check in to personal pagers were assessed along with creating environments that introduced ``passive distractions'' for <span class="hlt">acoustical</span> and <span class="hlt">noise</span> management, which can range from fireplaces, to coffee shops to playgrounds to ``tech corridors.'' While a number of these designs are currently being piloted, the over-reaching goal is to make the patient experience ``like no other'' when receiving their care at Mayo Clinic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988hias.rept.....G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988hias.rept.....G"><span>A high intensity <span class="hlt">acoustic</span> source for active attenuation of exhaust <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Glendinning, A. G.; Elliott, S. J.; Nelson, P. A.</p> <p>1988-04-01</p> <p>An electropneumatic sound source was developed for active <span class="hlt">noise</span> control systems applied in hostile environments such as the exhaust systems of gas turbines and internal combustion engines. It employs a gas bearing to support the friction free motion of a sliding plate which is used to modulate the supply of compressed air. The sliding plate is driven by an electrodynamic vibrator. Experimental results demonstrate that this arrangement reduces harmonic distortion to at least 20 dB below the fundamental driving frequency for most operating conditions. A theoretical analysis of the transducer enables predictions to be made of the <span class="hlt">acoustic</span> volume velocity (source strength) produced by the transducer as a function of the upstream pressure and displacement of the sliding valve. Applicability of the transducer to gas turbine and internal combustion engine exhaust systems was tested, and net power consumption resulting from the operation of the device was estimated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JPhCS.744a2148J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JPhCS.744a2148J"><span>Development of a model to assess <span class="hlt">acoustic</span> treatments to reduce railway <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jeong, H.; Squicciarini, G.; Thompson, D. J.; Ryue, J.</p> <p>2016-09-01</p> <p>Porous materials have recently been used in absorptive treatments around railway tracks to reduce <span class="hlt">noise</span> emissions. To investigate the effect of porous materials, a finite element model has been developed. 2D models for porous materials have been considered either as an equivalent fluid or as a poroelastic material based on the Biot theory. The two models have been validated and compared with each other to check the effect of the skeleton vibration. The poroelastic FE model has been coupled with a 2D <span class="hlt">acoustic</span> boundary element model for use in railway applications. The results show that it may be necessary to include the frame vibration, especially at low frequencies where a frame resonance occurs. A method for the characterization of porous materials is also discussed. From this it is shown that the elastic properties of the material determine the resonance frequency and the magnitude.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ASAJ..118.3086P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ASAJ..118.3086P"><span>Optimal virtual sensing for active <span class="hlt">noise</span> control in a rigid-walled <span class="hlt">acoustic</span> duct</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petersen, Dick; Zander, Anthony C.; Cazzolato, Ben S.; Hansen, Colin H.</p> <p>2005-11-01</p> <p>The performance of local active <span class="hlt">noise</span> control systems is generally limited by the small sizes of the zones of quiet created at the error sensors. This is often exacerbated by the fact that the error sensors cannot always be located close to an observer's ears. Virtual sensing is a method that can move the zone of quiet away from the physical location of the transducers to a desired location, such as an observer's ear. In this article, analytical expressions are derived for optimal virtual sensing in a rigid-walled <span class="hlt">acoustic</span> duct with arbitrary termination conditions. The expressions are derived for tonal excitations, and are obtained by employing a traveling wave model of a rigid-walled <span class="hlt">acoustic</span> duct. It is shown that the optimal solution for the virtual sensing microphone weights is independent of the source location and microphone locations. It is also shown that, theoretically, it is possible to obtain infinite reductions at the virtual location. The analytical expressions are compared with forward difference prediction techniques. The results demonstrate that the maximum attenuation, that theoretically can be obtained at the virtual location using forward difference prediction techniques, is expected to decrease for higher excitation frequencies and larger virtual distances.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12710923','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12710923"><span>Predicting mass rapid transit <span class="hlt">noise</span> <span class="hlt">levels</span> on an elevated station.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pamanikabud, Pichai; Paoprayoon, Suwajchai</p> <p>2003-04-01</p> <p>This study developed a <span class="hlt">noise</span> prediction model for elevated mass rapid transit (MRT) platforms. Relevant physical and operational parameters (e.g. cruise speed, acceleration and deceleration rates for trains, building façade setbacks and so on) were collected from the Bangkok mass transit system (BTS), the first elevated MRT system operated in Bangkok, Thailand. The equivalent continuous sound pressure <span class="hlt">levels</span> (L(Aeq)) were collected from both sides of the MRT stations at the center of each platform. The relevant parameters were collected on both platforms and ground <span class="hlt">level</span>, on both sides of MRT stations. These parameters were statistically tested to determine their correlation with MRT <span class="hlt">noise</span>. The final model was built from highly correlated parameters using multiple regression analysis with a stepwise regression technique. Statistical evaluation showed a high degree of goodness-of-fit test for the model to the observed data. Therefore, it can be efficiently used for the projection of MRT <span class="hlt">noise</span> in the affected areas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910062646&hterms=ionograms&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dionograms','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910062646&hterms=ionograms&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dionograms"><span>Wideband <span class="hlt">noise</span> observed at ground <span class="hlt">level</span> in the auroral region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Benson, Robert F.; Desch, Michael D.</p> <p>1991-01-01</p> <p>A sideband <span class="hlt">noise</span> event was detected at ground <span class="hlt">level</span> from the Andoya Rocket Range in Norway in January 1989. The signals were observed on four commercial communication receivers (tuned to 159, 515, 905, and 1200 kHz), an ionosonde (200-kHz to 3.5-MHz interference-free observations) and a riometer (32.5 MHz). The event, which occurred during a period of magnetic disturbance near magnetic midnight, was the only one observed during nearly 3 weeks of operations. This low frequency-of-occurrence is attributed partly to high local <span class="hlt">noise</span> <span class="hlt">levels</span>. The ease with which this event was identified on the ionograms produced by the local ionosonde suggests that routine ionosonde recordings should be inspected in search for such events. Such an effort would enhance existing research directed toward developing techniques for identifying quiet communication channels and help to identify the origin and frequency-of-occurrence of high-latitude wideband <span class="hlt">noise</span> events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5152973','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5152973"><span>Wideband <span class="hlt">noise</span> observed at ground <span class="hlt">level</span> in the auroral region</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Benson, R.F.; Desch, M.D. )</p> <p>1991-08-01</p> <p>A sideband <span class="hlt">noise</span> event was detected at ground <span class="hlt">level</span> from the Andoya Rocket Range in Norway in January 1989. The signals were observed on four commercial communication receivers (tuned to 159, 515, 905, and 1200 kHz), an ionosonde (200-kHz to 3.5-MHz interference-free observations) and a riometer (32.5 MHz). The event, which occurred during a period of magnetic disturbance near magnetic midnight, was the only one observed during nearly 3 weeks of operations. This low frequency-of-occurrence is attributed partly to high local <span class="hlt">noise</span> <span class="hlt">levels</span>. The ease with which this event was identified on the ionograms produced by the local ionosonde suggests that routine ionosonde recordings should be inspected in search for such events. Such an effort would enhance existing research directed toward developing techniques for identifying quiet communication channels and help to identify the origin and frequency-of-occurrence of high-latitude wideband <span class="hlt">noise</span> events. 20 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4752708','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4752708"><span>Low stimulus environments: reducing <span class="hlt">noise</span> <span class="hlt">levels</span> in continuing care</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Brown, Juliette; Fawzi, Waleed; Shah, Amar; Joyce, Margaret; Holt, Genevieve; McCarthy, Cathy; Stevenson, Carmel; Marange, Rosca; Shakes, Joy; Solomon-Ayeh, Kwesi</p> <p>2016-01-01</p> <p>In the low stimulus environment project, we aimed to reduce the <span class="hlt">levels</span> of intrusive background <span class="hlt">noise</span> on an older adult mental health ward, combining a very straightforward measure on decibel <span class="hlt">levels</span> with a downstream measure of reduced distress and agitation as expressed in incidents of violence. This project on reducing background <span class="hlt">noise</span> <span class="hlt">levels</span> on older adult wards stemmed from work the team had done on reducing <span class="hlt">levels</span> of violence and aggression. We approached the problem using quality improvement methods. Reducing harm to patients and staff is a strategic aim of our Trust and in our efforts we were supported by the Trust's extensive programme of quality improvement, including training and support provided by the Institute for Healthcare Improvement and the trust's own Quality Improvement team. Prior to the project we were running a weekly multi-disciplinary quality improvement group on the ward. We established from this a sub-group to address the specific problem of <span class="hlt">noise</span> <span class="hlt">levels</span> and invited carers of people with dementia on our ward to the group. The project was led by nursing staff. We used a <span class="hlt">noise</span> meter app readily downloadable from the internet to monitor background <span class="hlt">noise</span> <span class="hlt">levels</span> on the ward and establish a baseline measure. As a group we used a driver diagram to identify an overall aim and a clear understanding of the major factors that would drive improvements. We also used a staff and carer survey to identify further areas to work on. Change ideas that came from staff and carers included the use of the <span class="hlt">noise</span> meter to track and report back on <span class="hlt">noise</span> <span class="hlt">levels</span>, the use of posters to remind staff about <span class="hlt">noise</span> <span class="hlt">levels</span>, the introduction of a visual indication of current <span class="hlt">noise</span> <span class="hlt">levels</span> (the Yacker Tracker), the addition of relaxing background music, and adaptations to furniture and environment. We tested many of these over the course of nine months in 2015, using the iterative learning gained from multiple PDSA cycles. The specific aim was a decrease from above 60dB to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19206896','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19206896"><span>Variability in ambient <span class="hlt">noise</span> <span class="hlt">levels</span> and call parameters of North Atlantic right whales in three habitat areas.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Parks, Susan E; Urazghildiiev, Ildar; Clark, Christopher W</p> <p>2009-02-01</p> <p>The North Atlantic right whale inhabits the coastal waters off the east coasts of the United States and Canada, areas characterized by high <span class="hlt">levels</span> of shipping and fishing activities. <span class="hlt">Acoustic</span> communication plays an important role in the social behavior of these whales and increases in low-frequency <span class="hlt">noise</span> may be leading to changes in their calling behavior. This study characterizes the ambient <span class="hlt">noise</span> <span class="hlt">levels</span>, including both natural and anthropogenic sources, and right whale upcall parameters in three right whale habitat areas. Continuous recordings were made seasonally using autonomous bottom-mounted recorders in the Bay of Fundy, Canada (2004, 2005), Cape Cod Bay, (2005, 2006), and off the coast of Georgia (2004-2005, 2006-2007). Consistent interannual trends in <span class="hlt">noise</span> parameters were found for each habitat area, with both the band <span class="hlt">level</span> and spectrum <span class="hlt">level</span> measurements higher in the Bay of Fundy than in the other areas. Measured call parameters varied between habitats and between years within the same habitat area, indicating that habitat area and <span class="hlt">noise</span> <span class="hlt">levels</span> alone are not sufficient to predict variability in call parameters. These results suggest that right whales may be responding to the peak frequency of <span class="hlt">noise</span>, rather than the absolute <span class="hlt">noise</span> <span class="hlt">level</span> in their environment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27493778','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27493778"><span>Anthropogenic <span class="hlt">noise</span>, but not artificial light <span class="hlt">levels</span> predicts song behaviour in an equatorial bird.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dorado-Correa, Adriana M; Rodríguez-Rocha, Manuel; Brumm, Henrik</p> <p>2016-07-01</p> <p>Birds in cities start singing earlier in the morning than in rural areas; commonly this shift is attributed to light pollution. Some studies have suggested that traffic <span class="hlt">noise</span> has a stronger influence on singing activity than artificial light does. Changes in the timing of singing behaviour in relation to <span class="hlt">noise</span> and light pollution have only been investigated in the temperate zones. Tropical birds, however, experience little seasonal variation in day length and may be less dependent on light intensity as a modifier for reproductive behaviours such as song. To test whether <span class="hlt">noise</span> or light pollution has a stronger impact on the dawn chorus of a tropical bird, we investigated the singing behaviour of rufous-collared sparrows (Zonotrichia capensis) in Bogota, Colombia at two times during the year. We found that birds in places with high <span class="hlt">noise</span> <span class="hlt">levels</span> started to sing earlier. Light pollution did not have a significant effect. Birds may begin to sing earlier in noisy areas to avoid <span class="hlt">acoustic</span> masking by traffic later in the morning. Our results also suggest that some tropical birds may be less sensitive to variations in day length and thus less sensitive to light pollution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4968470','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4968470"><span>Anthropogenic <span class="hlt">noise</span>, but not artificial light <span class="hlt">levels</span> predicts song behaviour in an equatorial bird</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Rodríguez-Rocha, Manuel; Brumm, Henrik</p> <p>2016-01-01</p> <p>Birds in cities start singing earlier in the morning than in rural areas; commonly this shift is attributed to light pollution. Some studies have suggested that traffic <span class="hlt">noise</span> has a stronger influence on singing activity than artificial light does. Changes in the timing of singing behaviour in relation to <span class="hlt">noise</span> and light pollution have only been investigated in the temperate zones. Tropical birds, however, experience little seasonal variation in day length and may be less dependent on light intensity as a modifier for reproductive behaviours such as song. To test whether <span class="hlt">noise</span> or light pollution has a stronger impact on the dawn chorus of a tropical bird, we investigated the singing behaviour of rufous-collared sparrows (Zonotrichia capensis) in Bogota, Colombia at two times during the year. We found that birds in places with high <span class="hlt">noise</span> <span class="hlt">levels</span> started to sing earlier. Light pollution did not have a significant effect. Birds may begin to sing earlier in noisy areas to avoid <span class="hlt">acoustic</span> masking by traffic later in the morning. Our results also suggest that some tropical birds may be less sensitive to variations in day length and thus less sensitive to light pollution. PMID:27493778</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100026469','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100026469"><span>A Study of <span class="hlt">Acoustic</span> Reflections in Full-Scale Rotor Low Frequency <span class="hlt">Noise</span> Measurements Acquired in Wind Tunnels</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Barbely, Natasha L.; Sim, Ben W.; Kitaplioglu, Cahit; Goulding, Pat, II</p> <p>2010-01-01</p> <p>Difficulties in obtaining full-scale rotor low frequency <span class="hlt">noise</span> measurements in wind tunnels are addressed via residual sound reflections due to non-ideal anechoic wall treatments. Examples illustrated with the Boeing-SMART rotor test in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel facility demonstrated that these reflections introduced distortions in the measured <span class="hlt">acoustic</span> time histories that are not representative of free-field rotor <span class="hlt">noise</span> radiation. A simplified reflection analysis, based on the method of images, is used to examine the sound measurement quality in such "less-than-anechoic" environment. Predictions of reflection-adjusted <span class="hlt">acoustic</span> time histories are qualitatively shown to account for some of the spurious fluctuations observed in wind tunnel <span class="hlt">noise</span> measurements</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoRL..41.3096T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoRL..41.3096T"><span>High-speed imaging, <span class="hlt">acoustic</span> features, and aeroacoustic computations of jet <span class="hlt">noise</span> from Strombolian (and Vulcanian) explosions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Taddeucci, J.; Sesterhenn, J.; Scarlato, P.; Stampka, K.; Del Bello, E.; Pena Fernandez, J. J.; Gaudin, D.</p> <p>2014-05-01</p> <p>High-speed imaging of explosive eruptions at Stromboli (Italy), Fuego (Guatemala), and Yasur (Vanuatu) volcanoes allowed visualization of pressure waves from seconds-long explosions. From the explosion jets, waves radiate with variable geometry, timing, and apparent direction and velocity. Both the explosion jets and their wave fields are replicated well by numerical simulations of supersonic jets impulsively released from a pressurized vessel. The scaled <span class="hlt">acoustic</span> signal from one explosion at Stromboli displays a frequency pattern with an excellent match to those from the simulated jets. We conclude that both the observed waves and the audible sound from the explosions are jet <span class="hlt">noise</span>, i.e., the typical <span class="hlt">acoustic</span> field radiating from high-velocity jets. Volcanic jet <span class="hlt">noise</span> was previously quantified only in the infrasonic emissions from large, sub-Plinian to Plinian eruptions. Our combined approach allows us to define the spatial and temporal evolution of audible jet <span class="hlt">noise</span> from supersonic jets in small-scale volcanic eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24810556','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24810556"><span>Effect of external classroom <span class="hlt">noise</span> on schoolchildren's reading and mathematics performance: correlation of <span class="hlt">noise</span> <span class="hlt">levels</span> and gender.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Papanikolaou, M; Skenteris, N; Piperakis, S M</p> <p>2015-02-01</p> <p>The present study investigated the effect of low, medium, and high traffic road <span class="hlt">noise</span> as well as irrelevant background speech <span class="hlt">noise</span> on primary school children's reading and mathematical performance. A total of 676 participants (324 boys, 47.9% and 352 girls, 52.1%) of the 4th and 5th elementary classes participated in the project. The participants were enrolled in public primary schools from urban areas and had ages ranging from 9 to 10 years and from. Schools were selected on the basis of increasing <span class="hlt">levels</span> of exposure to road traffic <span class="hlt">noise</span> and then classified into three categories (Low <span class="hlt">noise</span>: 55-66 dB, Medium <span class="hlt">noise</span>: 67-77 dB, and High <span class="hlt">noise</span>: 72-80 dB). We measured reading comprehension and mathematical skills in accordance with the national guidelines for elementary education, using a test designed specifically for the purpose of this study. On the one hand, children in low-<span class="hlt">level</span> <span class="hlt">noise</span> schools showed statistically significant differences from children in medium- and high-<span class="hlt">level</span> <span class="hlt">noise</span> schools in reading performance (p<0.001). On the other hand, children in low-<span class="hlt">level</span> <span class="hlt">noise</span> schools differed significantly from children in high-<span class="hlt">level</span> <span class="hlt">noise</span> schools but only in mathematics performance (p=0.001). Girls in general did better in reading score than boys, especially in schools with medium- and high-<span class="hlt">level</span> <span class="hlt">noise</span>. Finally the <span class="hlt">levels</span> of <span class="hlt">noise</span> and gender were found to be two independent factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790023884','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790023884"><span><span class="hlt">Acoustic</span> plane waves normally incident on a clamped panel in a rectangular duct. [to explain <span class="hlt">noise</span> reduction curves for reducing interior <span class="hlt">noise</span> in aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Unz, H.; Roskam, J.</p> <p>1979-01-01</p> <p>The theory of <span class="hlt">acoustic</span> plane wave normally incident on a clamped panel in a rectangular duct is developed. The coupling theory between the elastic vibrations of the panel (plate) and the <span class="hlt">acoustic</span> wave propagation in infinite space and in the rectangular duct is considered. The partial differential equation which governs the vibration of the panel (plate) is modified by adding to its stiffness (spring) forces and damping forces, and the fundamental resonance frequency and the attenuation factor are discussed. The <span class="hlt">noise</span> reduction expression based on the theory is found to agree well with the corresponding experimental data of a sample aluminum panel in the mass controlled region, the damping controlled region, and the stiffness controlled region. All the frequency positions of the upward and downward resonance spikes in the sample experimental data are identified theoretically as resulting from four cross interacting major resonance phenomena: the cavity resonance, the <span class="hlt">acoustic</span> resonance, the plate resonance, and the wooden back panel resonance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000040432','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000040432"><span>Active Structural <span class="hlt">Acoustic</span> Control of Interior <span class="hlt">Noise</span> on a Raytheon 1900D</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Palumbo, Dan; Cabell, Ran; Sullivan, Brenda; Cline, John</p> <p>2000-01-01</p> <p>An active structural <span class="hlt">acoustic</span> control system has been demonstrated on a Raytheon Aircraft Company 1900D turboprop airliner. Both single frequency and multi-frequency control of the blade passage frequency and its harmonics was accomplished. The control algorithm was a variant of the popular filtered-x LMS implemented in the principal component domain. The control system consisted of 21 inertial actuators and 32 microphones. The actuators were mounted to the aircraft's ring frames. The microphones were distributed uniformly throughout the interior at head height, both seated and standing. Actuator locations were selected using a combinatorial search optimization algorithm. The control system achieved a 14 dB <span class="hlt">noise</span> reduction of the blade passage frequency during single frequency tests. Multi-frequency control of the first 1st, 2nd and 3rd harmonics resulted in 10.2 dB, 3.3 dB and 1.6 dB <span class="hlt">noise</span> reductions respectively. These results fall short of the predictions which were produced by the optimization algorithm (13.5 dB, 8.6 dB and 6.3 dB). The optimization was based on actuator transfer functions taken on the ground and it is postulated that cabin pressurization at flight altitude was a factor in this discrepancy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.S52B..01T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.S52B..01T"><span>Extraction of Stoneley and <span class="hlt">acoustic</span> Rayleigh waves from ambient <span class="hlt">noise</span> on ocean bottom observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tonegawa, T.; Fukao, Y.; Takahashi, T.; Obana, K.; Kodaira, S.; Kaneda, Y.</p> <p>2013-12-01</p> <p>In the interferometry, the wavefield propagating between two positions can be retrieved by correlating ambient <span class="hlt">noise</span> recorded on the two positions. This approach is useful for applying to various kinds of wavefield, such as ultrasonic, <span class="hlt">acoustic</span> (ocean <span class="hlt">acoustic</span>), and also seismology. Off the Kii Peninsula, Japan, more than 150 short-period (4.5 Hz) seismometers, in which hydrophone is also cosited, had been deployed for ~2 months on 2012 by Japan Agency for Marine-Earth Science and Technology (JAMSTEC) as a part of 'Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. In this study, correlating ambient <span class="hlt">noise</span> recorded on the sensors and hydrophones, we attempt to investigate characteristics of wavefield relative to the ocean, sediment, and solid-fluid boundary. The observation period is from Sep. 2012 to Dec. 2012. Station spacing is around 5 km. For 5 lines off the Kii Peninsula, the 30-40 seismometers are distributed at each line. Sampling interval is 200 Hz for both seismometer and hydrophone. The vertical component is just used in this study for correlation analysis. The instruments are located at 100-4800 m in water depth. In the processing for the both records, we applied a bandpass filter of 1-3 Hz, replaced the amplitude to zero if it exceeds a value that was set in this study, and took one-bit normalization. We calculated cross-correlation function (CCF) by using continuous records with a time length of 600 s, stacked the CCFs over the whole observation period. As a result of the analysis for hydrophone, a strong peak can be seen in the CCF for pairs of stations where the separation distance is ~5 km. Although the peak emerges in the CCFs for the separation distance up to 10 km, it disappears in the case that two stations are greater than 15 km separated. As a next approach, along a line off the Kii Peninsula, we aligned CCFs for two stations with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22559390','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22559390"><span>Sound <span class="hlt">level</span> discrimination by gray treefrogs in the presence and absence of chorus-shaped <span class="hlt">noise</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bee, Mark A; Vélez, Alejandro; Forester, James D</p> <p>2012-05-01</p> <p>An important aspect of hearing and <span class="hlt">acoustic</span> communication is the ability to discriminate differences in sound <span class="hlt">level</span>. Little is known about <span class="hlt">level</span> discrimination in anuran amphibians (frogs and toads), for which vocal communication in noisy social environments is often critical for reproduction. This study used two-choice phonotaxis tests to investigate the ability of females of Cope's gray treefrog (Hyla chrysoscelis) to discriminate between two advertisement calls differing only in sound pressure <span class="hlt">level</span> by 2, 4, or 6 dB. Tests were conducted in the presence and absence of chorus-shaped <span class="hlt">noise</span> (73 dB) and using two different ranges of signal <span class="hlt">levels</span> (73-79 dB and 79-85 dB). Females discriminated between two signals differing by as little as 2-4 dB. In contrast to expectations based on the "near miss to Weber's law" in birds and mammals, <span class="hlt">level</span> discrimination was slightly better at the lower range of signal amplitudes, a finding consistent with earlier studies of frogs and insects. Realistic <span class="hlt">levels</span> of background <span class="hlt">noise</span> simulating a breeding chorus had no discernable effect on discrimination at the sound <span class="hlt">level</span> differences tested in this study. These results have important implications for studies of auditory masking and signaling behavior in the contexts of anuran hearing and sound communication.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960047313','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960047313"><span>Validation of Aircraft <span class="hlt">Noise</span> Models at Lower <span class="hlt">Levels</span> of Exposure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Page, Juliet A.; Plotkin, Kenneth J.; Carey, Jeffrey N.; Bradley, Kevin A.</p> <p>1996-01-01</p> <p><span class="hlt">Noise</span> <span class="hlt">levels</span> around airports and airbases in the United States arc computed via the FAA's Integrated <span class="hlt">Noise</span> Model (INM) or the Air Force's NOISEMAP (NMAP) program. These models were originally developed for use in the vicinity of airports, at distances which encompass a day night average sound <span class="hlt">level</span> in decibels (Ldn) of 65 dB or higher. There is increasing interest in aircraft <span class="hlt">noise</span> at larger distances from the airport. including en-route <span class="hlt">noise</span>. To evaluate the applicability of INM and NMAP at larger distances, a measurement program was conducted at a major air carrier airport with monitoring sites located in areas exposed to an Ldn of 55 dB and higher. Automated Radar Terminal System (ARTS) radar tracking data were obtained to provide actual flight parameters and positive identification of aircraft. Flight operations were grouped according to aircraft type. stage length, straight versus curved flight tracks, and arrival versus departure. Sound exposure <span class="hlt">levels</span> (SEL) were computed at monitoring locations, using the INM, and compared with measured values. While individual overflight SEL data was characterized by a high variance, analysis performed on an energy-averaging basis indicates that INM and similar models can be applied to regions exposed to an Ldn of 55 dB with no loss of reliability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...377...90S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...377...90S"><span>Concurrent identification of aero-<span class="hlt">acoustic</span> scattering and <span class="hlt">noise</span> sources at a flow duct singularity in low Mach number flow</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sovardi, Carlo; Jaensch, Stefan; Polifke, Wolfgang</p> <p>2016-09-01</p> <p>A numerical method to concurrently characterize both aeroacoustic scattering and <span class="hlt">noise</span> sources at a duct singularity is presented. This approach combines Large Eddy Simulation (LES) with techniques of System Identification (SI): In a first step, a highly resolved LES with external broadband <span class="hlt">acoustic</span> excitation is carried out. Subsequently, time series data extracted from the LES are post-processed by means of SI to model both <span class="hlt">acoustic</span> propagation and <span class="hlt">noise</span> generation. The present work studies the aero-<span class="hlt">acoustic</span> characteristics of an orifice placed in a duct at low flow Mach numbers with the "LES-SI" method. Parametric SI based on the Box-Jenkins mathematical structure is employed, with a prediction error approach that utilizes correlation analysis of the output residuals to avoid overfitting. Uncertainties of model parameters due to the finite length of times series are quantified in terms of confidence intervals. Numerical results for <span class="hlt">acoustic</span> scattering matrices and power spectral densities of broad-band <span class="hlt">noise</span> are validated against experimental measurements over a wide range of frequencies below the cut-off frequency of the duct.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22087938','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22087938"><span>Effects of <span class="hlt">noise</span> <span class="hlt">levels</span> and call types on the source <span class="hlt">levels</span> of killer whale calls.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Holt, Marla M; Noren, Dawn P; Emmons, Candice K</p> <p>2011-11-01</p> <p>Accurate parameter estimates relevant to the vocal behavior of marine mammals are needed to assess potential effects of anthropogenic sound exposure including how masking <span class="hlt">noise</span> reduces the active space of sounds used for communication. Information about how these animals modify their vocal behavior in response to <span class="hlt">noise</span> exposure is also needed for such assessment. Prior studies have reported variations in the source <span class="hlt">levels</span> of killer whale sounds, and a more recent study reported that killer whales compensate for vessel masking <span class="hlt">noise</span> by increasing their call amplitude. The objectives of the current study were to investigate the source <span class="hlt">levels</span> of a variety of call types in southern resident killer whales while also considering background <span class="hlt">noise</span> <span class="hlt">level</span> as a likely factor related to call source <span class="hlt">level</span> variability. The source <span class="hlt">levels</span> of 763 discrete calls along with corresponding background <span class="hlt">noise</span> were measured over three summer field seasons in the waters surrounding the San Juan Islands, WA. Both <span class="hlt">noise</span> <span class="hlt">level</span> and call type were significant factors on call source <span class="hlt">levels</span> (1-40 kHz band, range of 135.0-175.7 dB(rms) re 1 [micro sign]Pa at 1 m). These factors should be considered in models that predict how anthropogenic masking <span class="hlt">noise</span> reduces vocal communication space in marine mammals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983eems.agar.....B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983eems.agar.....B"><span>Simulation of the <span class="hlt">acoustic</span> environment of a launcher and of the <span class="hlt">noise</span>-induced vibrations on its structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bourgine, A.</p> <p>1983-03-01</p> <p>During the launching and transonic flight of a launcher, high <span class="hlt">level</span> and wide-band frequency vibrations are transmitted to the payload and equipments. Preliminary simulation tests are planned to reproduce these dangerous phenomena; however, classical test facilities (reverberant <span class="hlt">acoustic</span> chambers) generally do not provide simultaneously the true space and time distribution of the flight pressure fluctuations. A method is described for forcing the vibratory response of the launcher wall, for instance at the shroud which shelters the satellite. (Statistical characteristics of this response are known by a previous analytical prediction). Forced vibrations are produced by using a few number of electrodynamic shakers acting on the wall; the N random forces are simultaneously synthesized on a digital computer. The proper simulation is realized when measured responses at N points exhibit spectral distributions and overall RMS <span class="hlt">levels</span> very close to the predicted flight values. Then, the <span class="hlt">noise</span> <span class="hlt">level</span> inside the shroud and the vibrations transmitted to the payload are also very close to the flight conditions. Some examples of applications to realistic structures, as the shroud of the Ariane vehicle, are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950011639','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950011639"><span>Background <span class="hlt">noise</span> <span class="hlt">levels</span> measured in the NASA Lewis 9- by 15-foot low-speed wind tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Woodward, Richard P.; Dittmar, James H.; Hall, David G.; Kee-Bowling, Bonnie</p> <p>1994-01-01</p> <p>The <span class="hlt">acoustic</span> capability of the NASA Lewis 9 by 15 Foot Low Speed Wind Tunnel has been significantly improved by reducing the background <span class="hlt">noise</span> <span class="hlt">levels</span> measured by in-flow microphones. This was accomplished by incorporating streamlined microphone holders having a profile developed by researchers at the NASA Ames Research Center. These new holders were fabricated for fixed mounting on the tunnel wall and for an axially traversing microphone probe which was mounted to the tunnel floor. Measured in-flow <span class="hlt">noise</span> <span class="hlt">levels</span> in the tunnel test section were reduced by about 10 dB with the new microphone holders compared with those measured with the older, less refined microphone holders. Wake interference patterns between fixed wall microphones were measured and resulted in preferred placement patterns for these microphones to minimize these effects. <span class="hlt">Acoustic</span> data from a model turbofan operating in the tunnel test section showed that results for the fixed and translating microphones were equivalent for common azimuthal angles, suggesting that the translating microphone probe, with its significantly greater angular resolution, is preferred for sideline <span class="hlt">noise</span> measurements. Fixed microphones can provide a local check on the traversing microphone data quality, and record <span class="hlt">acoustic</span> performance at other azimuthal angles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PhDT.......290S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PhDT.......290S"><span>Investigation into the response of the auditory and <span class="hlt">acoustic</span> communications systems in the Beluga whale (Delphinapterus leucas) of the St. Lawrence River Estuary to <span class="hlt">noise</span>, using vocal classification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scheifele, Peter Martin</p> <p>2003-06-01</p> <p><span class="hlt">Noise</span> pollution has only recently become recognized as a potential danger to marine mammals in general, and to the Beluga Whale (Delphinapterus leucas) in particular. These small gregarious Odontocetes make extensive use of sound for social communication and pod cohesion. The St. Lawrence River Estuary is habitat to a small, critically endangered population of about 700 Beluga whales who congregate in four different sites in its upper estuary. The population is believed to be threatened by the stress of high-intensity, low frequency <span class="hlt">noise</span>. One way to determine whether <span class="hlt">noise</span> is having an effect on an animal's auditory ability might be to observe a natural and repeatable response of the auditory and vocal systems to varying <span class="hlt">noise</span> <span class="hlt">levels</span>. This can be accomplished by observing changes in animal vocalizations in response to auditory feedback. A response such as this observed in humans and some animals is known as the Lombard Vocal Response, which represents a reaction of the auditory system directly manifested by changes in vocalization <span class="hlt">level</span>. In this research this population of Beluga Whales was tested to determine whether a vocalization-as-a-function-of-<span class="hlt">noise</span> phenomenon existed by using Hidden Markhov "classified" vocalizations as targets for <span class="hlt">acoustical</span> analyses. Correlation and regression analyses indicated that the phenomenon does exist and results of a human subjects experiment along with results from other animal species known to exhibit the response strongly implicate the Lombard Vocal Response in the Beluga.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OEng....6...77S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OEng....6...77S"><span><span class="hlt">Noise</span> <span class="hlt">level</span> arrangement in determined zones of homogenous development of green areas on the example of the spa park in Inowrocław</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sztubecka, Małgorzata; Skiba, Marta</p> <p>2016-11-01</p> <p><span class="hlt">Noise</span> measurements are usually carried out in developed areas as well as in the surroundings of traffic routes providing basis for actions in order to limit its influence on the neighboring areas. <span class="hlt">Noise</span> measurements in park areas are rare due to belief that these areas are silent zones. Such attitude cannot be justified. This article aims to the assessment of <span class="hlt">noise</span> appearing in determined subzones of the spa park in Inowrocław. From the research carried out it can be noticed that traffic <span class="hlt">noise</span> does not have any important meaning for the <span class="hlt">acoustic</span> climate of the park. It is the people who stay there who generate more <span class="hlt">noise</span>. Comparative analysis proves the appearance and penetration of <span class="hlt">noise</span> from the zones with greater <span class="hlt">level</span> of <span class="hlt">noise</span> to the ones with lower amount.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JSMTE..11..021V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JSMTE..11..021V"><span>Analysis of fractional Gaussian <span class="hlt">noises</span> using <span class="hlt">level</span> crossing method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vahabi, M.; Jafari, G. R.; Sadegh Movahed, M.</p> <p>2011-11-01</p> <p>The so-called <span class="hlt">level</span> crossing analysis has been used to investigate the empirical data set, but there is a lack of interpretation for what is reflected by the <span class="hlt">level</span> crossing results. The fractional Gaussian <span class="hlt">noise</span> as a well-defined stochastic series could be a suitable benchmark to make more sense of the <span class="hlt">level</span> crossing findings. In this paper, we calculated the average frequency of upcrossing for a wide range of fractional Gaussian <span class="hlt">noises</span> from logarithmic (zero Hurst exponent, H = 0), to Gaussian, H = 1 (0 < H < 1). By introducing the relative change of the total number of upcrossings for original data with respect to the so-called shuffled data, {R} , an empirical function for the Hurst exponent versus {R} has been established. Finally to make the concept more obvious, we applied this approach to some financial series.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26093410','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26093410"><span>Urban <span class="hlt">noise</span> functional stratification for estimating average annual sound <span class="hlt">level</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rey Gozalo, Guillermo; Barrigón Morillas, Juan Miguel; Prieto Gajardo, Carlos</p> <p>2015-06-01</p> <p>Road traffic <span class="hlt">noise</span> causes many health problems and the deterioration of the quality of urban life; thus, adequate spatial <span class="hlt">noise</span> and temporal assessment methods are required. Different methods have been proposed for the spatial evaluation of <span class="hlt">noise</span> in cities, including the categorization method. Until now, this method has only been applied for the study of spatial variability with measurements taken over a week. In this work, continuous measurements of 1 year carried out in 21 different locations in Madrid (Spain), which has more than three million inhabitants, were analyzed. The annual average sound <span class="hlt">levels</span> and the temporal variability were studied in the proposed categories. The results show that the three proposed categories highlight the spatial <span class="hlt">noise</span> stratification of the studied city in each period of the day (day, evening, and night) and in the overall indicators (L(And), L(Aden), and L(A24)). Also, significant differences between the diurnal and nocturnal sound <span class="hlt">levels</span> show functional stratification in these categories. Therefore, this functional stratification offers advantages from both spatial and temporal perspectives by reducing the sampling points and the measurement time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26584069','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26584069"><span>Combined <span class="hlt">acoustical</span> and visual performance of <span class="hlt">noise</span> barriers in mitigating the environmental impact of motorways.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Jiang, Like; Kang, Jian</p> <p>2016-02-01</p> <p>This study investigated the overall performance of <span class="hlt">noise</span> barriers in mitigating environmental impact of motorways, taking into consideration their effects on reducing <span class="hlt">noise</span> and visual intrusions of moving traffic, but also potentially inducing visual impact themselves. A laboratory experiment was carried out, using computer-visualised video scenes and motorway traffic <span class="hlt">noise</span> recordings to present experimental scenarios covering two traffic <span class="hlt">levels</span>, two distances of receiver to road, two types of background landscape, and five barrier conditions including motorway only, motorway with tree belt, motorways with 3 m timber barrier, 5m timber barrier, and 5m transparent barrier. Responses from 30 participants of university students were gathered and perceived barrier performance analysed. The results show that <span class="hlt">noise</span> barriers were always beneficial in mitigating environmental impact of motorways, or made no significant changes in environmental quality when the impact of motorways was low. Overall, barriers only offered similar mitigation effect as compared to tree belt, but showed some potential to be more advantageous when traffic <span class="hlt">level</span> went high. 5m timber barrier tended to perform better than the 3m one at the distance of 300 m but not at 100 m possibly due to its negative visual effect when getting closer. The transparent barrier did not perform much differently from the timber barriers but tended to be the least effective in most scenarios. Some low positive correlations were found between aesthetic preference for barriers and environmental impact reduction by the barriers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000101661','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000101661"><span>Current Background <span class="hlt">Noise</span> Sources and <span class="hlt">Levels</span> in the NASA Ames 40- by 80-Foot Wind Tunnel: A Status Report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allen, Christopher S.; Jaeger, Stephen; Soderman, Paul; Koga, Dennis (Technical Monitor)</p> <p>1999-01-01</p> <p>Background <span class="hlt">noise</span> measurements were made of the <span class="hlt">acoustic</span> environment in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The measurements were acquired subsequent to the 40x80 Aeroacoustic Modernization Project, which was undertaken to improve the anechoic characteristics of the 40x80's closed test section as well as reduce the <span class="hlt">levels</span> of background <span class="hlt">noise</span> in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background <span class="hlt">noise</span>, discusses the sources of the <span class="hlt">noise</span>, and draws comparisons to previous 40x80 background <span class="hlt">noise</span> <span class="hlt">levels</span> measurements. At low wind speeds or low frequencies, the 40x80 background <span class="hlt">noise</span> is dominated by the fan drive system. To obtain the lowest fan drive <span class="hlt">noise</span> for a given tunnel condition, it is possible in the 40x80 to reduce the fans' rotational speed and adjust the fans' blade pitch, as described by Schmidtz et. al. This idea is not new, but has now been operationally implemented with modifications for increased power at low rotational speeds. At low to mid-frequencies and at higher wind speeds, the dominant <span class="hlt">noise</span> mechanism was thought to be caused by the surface interface of the previous test section floor <span class="hlt">acoustic</span> lining. In order to reduce this <span class="hlt">noise</span> mechanism, the new test section floor lining was designed to resist the pumping of flow in and out of the space between the grating slats required to support heavy equipment. In addition, the lining/flow interface over the entire test section was designed to be smoother and quieter than the previous design. At high wind speeds or high frequencies, the dominant source of background <span class="hlt">noise</span> in the 40x80 is believed to be caused by the response of the in-flow microphone probes (required by the nature of the closed test section) to the fluctuations in the freestream flow. The resulting background <span class="hlt">noise</span> <span class="hlt">levels</span> are also different for probes of various</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol2/pdf/CFR-2012-title14-vol2-sec91-859.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol2/pdf/CFR-2012-title14-vol2-sec91-859.pdf"><span>14 CFR 91.859 - Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-01-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">levels</span>. 91.859 Section 91.859 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... <span class="hlt">Noise</span> Limits § 91.859 Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>. For an airplane subject to... Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title33-vol2/pdf/CFR-2011-title33-vol2-sec149-697.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title33-vol2/pdf/CFR-2011-title33-vol2-sec149-697.pdf"><span>33 CFR 149.697 - What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey?</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-07-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">level</span> survey? 149.697 Section 149.697 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF... and Equipment <span class="hlt">Noise</span> Limits § 149.697 What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey? (a) A survey to determine the maximum <span class="hlt">noise</span> <span class="hlt">level</span> during normal operations must be conducted in each...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title33-vol2/pdf/CFR-2012-title33-vol2-sec149-697.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title33-vol2/pdf/CFR-2012-title33-vol2-sec149-697.pdf"><span>33 CFR 149.697 - What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey?</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-07-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">level</span> survey? 149.697 Section 149.697 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF... and Equipment <span class="hlt">Noise</span> Limits § 149.697 What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey? (a) A survey to determine the maximum <span class="hlt">noise</span> <span class="hlt">level</span> during normal operations must be conducted in each...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title14-vol2/pdf/CFR-2013-title14-vol2-sec91-859.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title14-vol2/pdf/CFR-2013-title14-vol2-sec91-859.pdf"><span>14 CFR 91.859 - Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-01-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">levels</span>. 91.859 Section 91.859 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... <span class="hlt">Noise</span> Limits § 91.859 Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>. For an airplane subject to... Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2010-title14-vol2/pdf/CFR-2010-title14-vol2-sec91-859.pdf','CFR'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2010-title14-vol2/pdf/CFR-2010-title14-vol2-sec91-859.pdf"><span>14 CFR 91.859 - Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2010&page.go=Go">Code of Federal Regulations, 2010 CFR</a></p> <p></p> <p>2010-01-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">levels</span>. 91.859 Section 91.859 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... <span class="hlt">Noise</span> Limits § 91.859 Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>. For an airplane subject to... Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol2/pdf/CFR-2014-title14-vol2-sec91-859.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol2/pdf/CFR-2014-title14-vol2-sec91-859.pdf"><span>14 CFR 91.859 - Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-01-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">levels</span>. 91.859 Section 91.859 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... <span class="hlt">Noise</span> Limits § 91.859 Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>. For an airplane subject to... Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title33-vol2/pdf/CFR-2013-title33-vol2-sec149-697.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title33-vol2/pdf/CFR-2013-title33-vol2-sec149-697.pdf"><span>33 CFR 149.697 - What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey?</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-07-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">level</span> survey? 149.697 Section 149.697 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF... and Equipment <span class="hlt">Noise</span> Limits § 149.697 What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey? (a) A survey to determine the maximum <span class="hlt">noise</span> <span class="hlt">level</span> during normal operations must be conducted in each...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title49-vol5/pdf/CFR-2012-title49-vol5-sec393-94.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title49-vol5/pdf/CFR-2012-title49-vol5-sec393-94.pdf"><span>49 CFR 393.94 - Interior <span class="hlt">noise</span> <span class="hlt">levels</span> in power units.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-10-01</p> <p>... 49 Transportation 5 2012-10-01 2012-10-01 false Interior <span class="hlt">noise</span> <span class="hlt">levels</span> in power units. 393.94... <span class="hlt">noise</span> <span class="hlt">levels</span> in power units. (a) Applicability of this section. The interior <span class="hlt">noise</span> <span class="hlt">level</span> requirements..., if the reading has not been influenced by extraneous <span class="hlt">noise</span> sources such as motor vehicles...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title33-vol2/pdf/CFR-2014-title33-vol2-sec149-697.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title33-vol2/pdf/CFR-2014-title33-vol2-sec149-697.pdf"><span>33 CFR 149.697 - What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey?</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-07-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">level</span> survey? 149.697 Section 149.697 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF... and Equipment <span class="hlt">Noise</span> Limits § 149.697 What are the requirements for a <span class="hlt">noise</span> <span class="hlt">level</span> survey? (a) A survey to determine the maximum <span class="hlt">noise</span> <span class="hlt">level</span> during normal operations must be conducted in each...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title49-vol5/pdf/CFR-2014-title49-vol5-sec393-94.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title49-vol5/pdf/CFR-2014-title49-vol5-sec393-94.pdf"><span>49 CFR 393.94 - Interior <span class="hlt">noise</span> <span class="hlt">levels</span> in power units.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-10-01</p> <p>... 49 Transportation 5 2014-10-01 2014-10-01 false Interior <span class="hlt">noise</span> <span class="hlt">levels</span> in power units. 393.94... <span class="hlt">noise</span> <span class="hlt">levels</span> in power units. (a) Applicability of this section. The interior <span class="hlt">noise</span> <span class="hlt">level</span> requirements..., if the reading has not been influenced by extraneous <span class="hlt">noise</span> sources such as motor vehicles...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol2/pdf/CFR-2011-title14-vol2-sec91-859.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title14-vol2/pdf/CFR-2011-title14-vol2-sec91-859.pdf"><span>14 CFR 91.859 - Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-01-01</p> <p>... <span class="hlt">noise</span> <span class="hlt">levels</span>. 91.859 Section 91.859 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF... <span class="hlt">Noise</span> Limits § 91.859 Modification to meet Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>. For an airplane subject to... Stage 3 or Stage 4 <span class="hlt">noise</span> <span class="hlt">levels</span>....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19820045630&hterms=railway&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Drailway','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19820045630&hterms=railway&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Drailway"><span>Comparing the relationships between <span class="hlt">noise</span> <span class="hlt">level</span> and annoyance in different surveys - A railway <span class="hlt">noise</span> vs. aircraft and road traffic comparison</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Fields, J. M.; Walker, J. G.</p> <p>1982-01-01</p> <p>Annoyance expressed in a railway <span class="hlt">noise</span> survey is compared with that from two road traffic and three aircraft surveys in order to determine whether responses to various types of environmental <span class="hlt">noise</span> are source-specific. Railway <span class="hlt">noise</span> is found to be less annoying than other <span class="hlt">noises</span> at any given high <span class="hlt">noise</span> <span class="hlt">level</span>. Railway <span class="hlt">noise</span> annoyance rises less rapidly with increasing <span class="hlt">noise</span> <span class="hlt">level</span>. At high <span class="hlt">levels</span>, this gap in reactions averages about 10 dB; it ranges from 4 dB to more than 20 dB. The methods used for comparing the surveys are examined. It is found that methodological uncertainties lead to imprecise comparisons and that different annoyance scales yield different estimates of intersurvey differences.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NaPho..11...44X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NaPho..11...44X"><span>Photonic microwave signals with zeptosecond-<span class="hlt">level</span> absolute timing <span class="hlt">noise</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xie, Xiaopeng; Bouchand, Romain; Nicolodi, Daniele; Giunta, Michele; Hänsel, Wolfgang; Lezius, Matthias; Joshi, Abhay; Datta, Shubhashish; Alexandre, Christophe; Lours, Michel; Tremblin, Pierre-Alain; Santarelli, Giorgio; Holzwarth, Ronald; Le Coq, Yann</p> <p>2017-01-01</p> <p>Photonic synthesis of radiofrequency (RF) waveforms revived the quest for unrivalled microwave purity because of its ability to convey the benefits of optics to the microwave world. In this work, we perform a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-<span class="hlt">noise</span> fibre-based frequency comb and cutting-edge photodetection techniques. We demonstrate the generation of the purest microwave signal with a fractional frequency stability below 6.5 × 10-16 at 1 s and a timing <span class="hlt">noise</span> floor below 41 zs Hz-1/2 (phase <span class="hlt">noise</span> below -173 dBc Hz-1 for a 12 GHz carrier). This outperforms existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with the lowermost detection <span class="hlt">noise</span>. This unprecedented <span class="hlt">level</span> of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurement methods developed here can benefit the characterization of a broad range of signals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6707800','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6707800"><span>Radiation threshold <span class="hlt">levels</span> for <span class="hlt">noise</span> degradation of photodiodes. Technical report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Aukerman, L.W.; Vernon, F.L.; Song, Y.</p> <p>1986-09-30</p> <p>Space radiation can increase the <span class="hlt">noise</span> of photodiodes as a result of either a sustained ionizing-dose-rate effect or displacement damage. Elementary, straightforward models are presented for calculating radiation threshold <span class="hlt">levels</span> and rad hit susceptibility. Radiation-effects experiments that verify these models are discussed. Calculations for room-temperature silicon p-i-n photodetectors, an avalanche photodiode, and a hypothetical cooled staring detector indicate that this damage mechanism should not be ignored for space and nuclear environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5327586','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5327586"><span>A Trainable Hearing Aid Algorithm Reflecting Individual Preferences for Degree of <span class="hlt">Noise</span>-Suppression, Input Sound <span class="hlt">Level</span>, and Listening Situation</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Yoon, Sung Hoon; Nam, Kyoung Won; Yook, Sunhyun; Cho, Baek Hwan; Jang, Dong Pyo; Hong, Sung Hwa; Kim, In Young</p> <p>2017-01-01</p> <p>Objectives In an effort to improve hearing aid users’ satisfaction, recent studies on trainable hearing aids have attempted to implement one or two environmental factors into training. However, it would be more beneficial to train the device based on the owner’s personal preferences in a more expanded environmental <span class="hlt">acoustic</span> conditions. Our study aimed at developing a trainable hearing aid algorithm that can reflect the user’s individual preferences in a more extensive environmental <span class="hlt">acoustic</span> conditions (ambient sound <span class="hlt">level</span>, listening situation, and degree of <span class="hlt">noise</span> suppression) and evaluated the perceptual benefit of the proposed algorithm. Methods Ten normal hearing subjects participated in this study. Each subjects trained the algorithm to their personal preference and the trained data was used to record test sounds in three different settings to be utilized to evaluate the perceptual benefit of the proposed algorithm by performing the Comparison Mean Opinion Score test. Results Statistical analysis revealed that of the 10 subjects, four showed significant differences in amplification constant settings between the <span class="hlt">noise</span>-only and speech-in-<span class="hlt">noise</span> situation (P<0.05) and one subject also showed significant difference between the speech-only and speech-in-<span class="hlt">noise</span> situation (P<0.05). Additionally, every subject preferred different β settings for beamforming in all different input sound <span class="hlt">levels</span>. Conclusion The positive findings from this study suggested that the proposed algorithm has potential to improve hearing aid users’ personal satisfaction under various ambient situations. PMID:27507270</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA109848','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA109848"><span>Aerodynamic and <span class="hlt">Acoustic</span> Tests of a 1/15 Scale Model Dry Cooled Jet Aircraft Runup <span class="hlt">Noise</span> Suppression System,</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1975-10-01</p> <p>Temperature Contours for the Obround Augmenter with the Jet Centered (Position a, yp = 1.0) and Deflected Downward 3.60 165 Figure 7.3- 16 . Maximum Mixed...<span class="hlt">Acoustic</span> Tests -8- r7 FLUIDYNE ENGINEERING CORPORATION I 2.0.3 Aero-Thermal Testing (Test Series 13 through 16 ) I The aero-thermal testing, Figure...Excessive Augmenter Exit Flow <span class="hlt">Noise</span> <span class="hlt">Noise</span> One Engine at Two Engines at Criteria Max. RPM Max. RPM at 250 ft. AA/ANT a AA/A NT 95 dBA 18 16 85 dBA 24</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26519582','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26519582"><span>Assessment of an action against environmental <span class="hlt">noise</span>: <span class="hlt">Acoustic</span> durability of a pavement surface with crumb rubber.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vázquez, V F; Luong, J; Bueno, M; Terán, F; Paje, S E</p> <p>2016-01-15</p> <p>Environmental <span class="hlt">noise</span> is a worldwide problem that has an adverse effect in the quality of life of urban population. Some work has shown that there is a correlation between environmental <span class="hlt">noise</span> and health issues as sleep disturbance or annoyance. This study presents the time evolution of a test track fabricated with an asphalt mixture with 20% of crumb rubber by weight of bitumen, added by the wet process. A complete surface characterization has been performed by determining tire/pavement sound <span class="hlt">levels</span>, road texture profiles, in-situ dynamic stiffness and sound absorption of compacted and extracted sample cores. Two measurement campaigns were performed: just after mixture laying and after 3 years in service. This study confirms that the use of crumb rubber as a modifier of bituminous binders (CRMB) can improve the pavement characteristics: gap-graded mixtures with crumb rubber can be used in the action plans as urban rehabilitation measure to fight <span class="hlt">noise</span> pollution. However, this <span class="hlt">noise</span> reduction seems to decrease with age at a rate of approximately 0.15 dB(A) per year.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760003044','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760003044"><span>Effects of long-chord <span class="hlt">acoustically</span> treated stator vanes on fan <span class="hlt">noise</span>. 1: Effect of long chord (taped stator)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dittmar, J. H.; Scott, J. N.; Leonard, B. R.; Stakolich, E. G.</p> <p>1975-01-01</p> <p>A set of long-chord stator vanes was designed to replace the vanes in an existing fan stage. The long vanes consisted of a turning section and axial extension pieces, both of which incorporated <span class="hlt">acoustic</span> damping material. The <span class="hlt">acoustic</span> damping material was made inactive for these tests by covering with metal tape, and the stator vanes were tested in three length configurations. Compared to the values for the original stage, broadband <span class="hlt">noise</span> was reduced in the middle to high frequencies with the long stator vanes, but a broadband <span class="hlt">noise</span> increase was observed at the low frequencies. No change was observed in the blade passage tone, but some aft end reduction in the overtones was observed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4582459','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4582459"><span>Measurement of Acceptable <span class="hlt">Noise</span> <span class="hlt">Level</span> with Background Music</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ahn, Hyun-Jung; Bahng, Junghwa</p> <p>2015-01-01</p> <p>Background and Objectives Acceptable <span class="hlt">noise</span> <span class="hlt">level</span> (ANL) is a measure of the maximum background <span class="hlt">noise</span> <span class="hlt">level</span> (BNL) that a person is willing to tolerate while following a target story. Although researchers have used various sources of target sound in ANL measures, a limited type of background <span class="hlt">noise</span> has been used. Extending the previous study of Gordon-Hickey & Moore (2007), the current study determined the effect of music genre and tempo on ANLs as possible factors affecting ANLs. We also investigated the relationships between individual ANLs and the familiarity of music samples and between music ANLs and subjective preference. Subjects and Methods Forty-one participants were seperated into two groups according to their ANLs, 29 low-ANL listeners and 12 high-ANL listeners. Using Korean ANL material, the individual ANLs were measured based on the listeners' most comfortable listening <span class="hlt">level</span> and BNL. The ANLs were measured in six conditions, with different music tempo (fast, slow) and genre (K-pop, pop, classical) in a counterbalanced order. Results Overall, ANLs did not differ by the tempo of background music, but music genre significantly affected individual ANLs. We observed relatively higher ANLs with K-pop music and relatively lower ANLs with classical music. This tendency was similar in both low-ANL and high-ANL groups. However, the subjective ratings of music familiarity and preference affected ANLs differently for low-ANL and high-ANL groups. In contrast to the low-ANL listeners, the ANLs of the high-ANL listeners were significantly affected by music familiarity and preference. Conclusions The genre of background music affected ANLs obtained using background music. The degree of music familiarity and preference appears to be associated with individual susceptibility to background music only for listeners who are greatly annoyed by background <span class="hlt">noise</span> (high-ANL listeners). PMID:26413573</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4753415','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4753415"><span>Observation of the Kibble–Zurek Mechanism in Microscopic <span class="hlt">Acoustic</span> Crackling <span class="hlt">Noises</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ghaffari, H. O.; Griffth, W. A.; Benson, P.M.; Xia, K.; Young, R. P.</p> <p>2016-01-01</p> <p>Characterizing the fast evolution of microstructural defects is key to understanding “crackling” phenomena during the deformation of solid materials. For example, it has been proposed using atomistic simulations of crack propagation in elastic materials that the formation of a nonlinear hyperelastic or plastic zone around moving crack tips controls crack velocity. To date, progress in understanding the physics of this critical zone has been limited due to the lack of data describing the complex physical processes that operate near microscopic crack tips. We show, by analyzing many <span class="hlt">acoustic</span> emission events during rock deformation experiments, that the signature of this nonlinear zone maps directly to crackling <span class="hlt">noises</span>. In particular, we characterize a weakening zone that forms near the moving crack tips using functional networks, and we determine the scaling law between the formation of damages (defects) and the traversal rate across the critical point of transition. Moreover, we show that the correlation length near the transition remains effectively frozen. This is the main underlying hypothesis behind the Kibble-Zurek mechanism (KZM) and the obtained power-law scaling verifies the main prediction of KZM. PMID:26876156</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990PhDT.......134K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990PhDT.......134K"><span>Pitch Estimation, Voicing Decision, and <span class="hlt">Noise</span> Spectrum Estimation for Speech Corrupted by High <span class="hlt">Levels</span> of Additive <span class="hlt">Noise</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Krubsack, David Allan</p> <p>1990-01-01</p> <p>This dissertation presents two algorithms that extract parameters which are important to speech processing in high <span class="hlt">levels</span> of <span class="hlt">noise</span>. The first algorithm determines whether a signal containing <span class="hlt">noise</span> corrupted human speech is voiced or not and estimates the fundamental frequency (pitch) of voiced speech. The second algorithm produces an estimate of the additive <span class="hlt">noise</span> which is corrupting the speech. Previous research related to the voicing decision and pitch estimation has been concentrated at signal-to -<span class="hlt">noise</span> ratios (SNRs) above 0 dB. Consequently, speech processing requiring the extraction of these parameters in higher <span class="hlt">levels</span> of <span class="hlt">noise</span> could not be performed with much success. The research presented in this dissertation concentrates on SNRs around and below 0 dB. Although the algorithm, based on the autocorrelation function, is designed to work well for high <span class="hlt">levels</span> of <span class="hlt">noise</span>, good results for the no <span class="hlt">noise</span> case have been maintained. The idea of a confidence measure for parameter estimation is introduced. Confidence measures are defined and developed for both the voicing decision and the pitch estimation algorithms. Estimation of <span class="hlt">noise</span> that is corrupting a speech signal has been motivated by the need to enhance the corrupted speech. Previous research has concentrated on speech which is band limited to about 3500 Hz. Therefore, the estimation of the <span class="hlt">noise</span> corrupting high frequency speech had not been considered. The <span class="hlt">noise</span> estimation algorithm presented in this dissertation considers the effects of high frequency speech on the <span class="hlt">noise</span> estimate in addition to the effects of low frequency speech. A new spectral averaging method is introduced which significantly reduces the corrupting effect of the speech components on the <span class="hlt">noise</span> estimate for SNRs above 0 dB. The algorithm is tested for stationary white <span class="hlt">noise</span>, stationary non-white <span class="hlt">noise</span>, and non-stationary white <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150000891','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150000891"><span>Tone and Broadband <span class="hlt">Noise</span> Separation from <span class="hlt">Acoustic</span> Data of a Scale-Model Counter-Rotating Open Rotor</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sree, David; Stephens, David B.</p> <p>2014-01-01</p> <p>Renewed interest in contra-rotating open rotor technology for aircraft propulsion application has prompted the development of advanced diagnostic tools for better design and improved <span class="hlt">acoustical</span> performance. In particular, the determination of tonal and broadband components of open rotor <span class="hlt">acoustic</span> spectra is essential for properly assessing the <span class="hlt">noise</span> control parameters and also for validating the open rotor <span class="hlt">noise</span> simulation codes. The technique of phase averaging has been employed to separate the tone and broadband components from a single rotor, but this method does not work for the two-shaft contra-rotating open rotor. A new signal processing technique was recently developed to process the contra-rotating open rotor <span class="hlt">acoustic</span> data. The technique was first tested using <span class="hlt">acoustic</span> data taken of a hobby aircraft open rotor propeller, and reported previously. The intent of the present work is to verify and validate the applicability of the new technique to a realistic one-fifth scale open rotor model which has 12 forward and 10 aft contra-rotating blades operating at realistic forward flight Mach numbers and tip speeds. The results and discussions of that study are presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150002339','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002339"><span>Tone and Broadband <span class="hlt">Noise</span> Separation from <span class="hlt">Acoustic</span> Data of a Scale-Model Contra-Rotating Open Rotor</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sree, Dave; Stephens, David B.</p> <p>2014-01-01</p> <p>Renewed interest in contra-rotating open rotor technology for aircraft propulsion application has prompted the development of advanced diagnostic tools for better design and improved <span class="hlt">acoustical</span> performance. In particular, the determination of tonal and broadband components of open rotor <span class="hlt">acoustic</span> spectra is essential for properly assessing the <span class="hlt">noise</span> control parameters and also for validating the open rotor <span class="hlt">noise</span> simulation codes. The technique of phase averaging has been employed to separate the tone and broadband components from a single rotor, but this method does not work for the two-shaft contra-rotating open rotor. A new signal processing technique was recently developed to process the contra-rotating open rotor <span class="hlt">acoustic</span> data. The technique was first tested using <span class="hlt">acoustic</span> data taken of a hobby aircraft open rotor propeller, and reported previously. The intent of the present work is to verify and validate the applicability of the new technique to a realistic one-fifth scale open rotor model which has 12 forward and 10 aft contra-rotating blades operating at realistic forward flight Mach numbers and tip speeds. The results and discussions of that study are presented in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26411830','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26411830"><span>Creating a Culture of Safety by Reducing <span class="hlt">Noise</span> <span class="hlt">Levels</span> in the OR.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hogan, Lisa J; Harvey, Renee L</p> <p>2015-10-01</p> <p>We implemented a quality improvement project to reduce <span class="hlt">noise</span> <span class="hlt">levels</span> in the OR in response to complaints from the anesthesia staff members at two community hospitals. Excessive <span class="hlt">noise</span> has been shown to increase staff member stress, fatigue, distraction, and ineffective communication, which can lead to medical errors. We measured <span class="hlt">noise</span> <span class="hlt">levels</span> during anesthesia induction and emergence for 118 different surgical procedures and compared <span class="hlt">noise</span> <span class="hlt">levels</span> before and after the improvement project intervention. Staff member education and <span class="hlt">noise</span> reduction strategies, which included signage, prominent <span class="hlt">noise</span> meters, and specific suggestions to staff members, helped to significantly reduce the <span class="hlt">noise</span> <span class="hlt">level</span> during the anesthetic induction and emergence phases of OR procedures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JSV...332.2808S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JSV...332.2808S"><span>On the precise implications of <span class="hlt">acoustic</span> analogies for aerodynamic <span class="hlt">noise</span> at low Mach numbers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spalart, Philippe R.</p> <p>2013-05-01</p> <p>We seek a clear statement of the scaling which may be expected with rigour for transportation or other <span class="hlt">noise</span> at low Mach numbers M, based on Lighthill's and Curle's theories of 1952 and 1955. In the presence of compact solid bodies, the leading term in the <span class="hlt">acoustic</span> intensity is of order M6. Contrary to the belief held since that time that it is of order M8, the contribution of quadrupoles, in the presence of dipoles, is of order only M7. Retarded-time-difference effects are also of order M7. Curle's widely used approximation based on unsteady forces neglects both effects. Its order of accuracy is thus lower than was thought, and the common estimates of the value of M below which it applies appear precarious. The M6 leading term is modified by powers up to the fourth of (1-Mr), where Mr is the relative Mach number between source and observer; at speeds of interest the effect is several dB. However, this is only one of the corrections of order M7, which makes its value debatable. The same applies to the difference between emission distance and reception distance. The scaling with M6 is theoretically correct to leading order, but this prediction may be so convincing, like the M8 scaling for jet <span class="hlt">noise</span>, that some authors rush to confirm it when their measurements are in conflict with it. We survey experimental studies of landing-gear <span class="hlt">noise</span>, and argue that the observed power of M is often well below 6. We also object to comparisons across Mach numbers at fixed frequency; they should be made at fixed Strouhal number St instead. Finally, the compact-source argument does not only require M≪1; it requires MSt≪1. This is more restrictive if the relevant St is well above 1, a situation which can be caused by interference with a boundary or by wake impingement, among other effects. The best length scales to define St for this purpose are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860012833','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860012833"><span>Airport-<span class="hlt">Noise</span> <span class="hlt">Levels</span> and Annoyance Model (ALAMO) user's guide</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Deloach, R.; Donaldson, J. L.; Johnson, M. J.</p> <p>1986-01-01</p> <p>A guide for the use of the Airport-<span class="hlt">Noise</span> <span class="hlt">Level</span> and Annoyance MOdel (ALAMO) at the Langley Research Center computer complex is provided. This document is divided into 5 primary sections, the introduction, the purpose of the model, and an in-depth description of the following subsystems: baseline, <span class="hlt">noise</span> reduction simulation and track analysis. For each subsystem, the user is provided with a description of architecture, an explanation of subsystem use, sample results, and a case runner's check list. It is assumed that the user is familiar with the operations at the Langley Research Center (LaRC) computer complex, the Network Operating System (NOS 1.4) and CYBER Control Language. Incorporated within the ALAMO model is a census database system called SITE II.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150021043','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150021043"><span>Application of an Aligned and Unaligned Signal Processing Technique to Investigate Tones and Broadband <span class="hlt">Noise</span> in Fan and Contra-Rotating Open Rotor <span class="hlt">Acoustic</span> Spectra</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Miles, Jeffrey Hilton; Hultgren, Lennart S.</p> <p>2015-01-01</p> <p>The study of <span class="hlt">noise</span> from a two-shaft contra-rotating open rotor (CROR) is challenging since the shafts are not phase locked in most cases. Consequently, phase averaging of the <span class="hlt">acoustic</span> data keyed to a single shaft rotation speed is not meaningful. An unaligned spectrum procedure that was developed to estimate a signal coherence threshold and reveal concealed spectral lines in turbofan engine combustion <span class="hlt">noise</span> is applied to fan and CROR <span class="hlt">acoustic</span> data in this paper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22724316','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22724316"><span>Minimum requirement of artificial <span class="hlt">noise</span> <span class="hlt">level</span> for using <span class="hlt">noise</span>-assisted correlation algorithm to suppress artifacts in ultrasonic Nakagami images.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tsui, Po-Hsiang</p> <p>2012-04-01</p> <p>The Nakagami image is a complementary imaging mode for pulse-echo ultrasound B-scan to characterize tissues. White <span class="hlt">noise</span> in anechoic areas induces artifacts in the Nakagami image. Recently, we proposed a <span class="hlt">noise</span>-assisted correlation algorithm (NCA) for suppressing the Nakagami artifact. In the NCA, artificial white <span class="hlt">noise</span> is intentionally added twice to backscattered signals to produce two noisy data, which are used to establish a correlation profile for rejecting <span class="hlt">noise</span>. This study explored the effects of artificial <span class="hlt">noise</span> <span class="hlt">level</span> on the NCA to suppress the artifact of the Nakagami image. Simulations were conducted to produce B-mode images of anechoic regions under signal-to-<span class="hlt">noise</span> ratios (SNRs) of 20, 10 and 5 dB. Various artificial <span class="hlt">noise</span> <span class="hlt">levels</span> ranging from 0.1- to 1-fold of the intrinsic <span class="hlt">noise</span> amplitude were used in the NCA for constructing the Nakagami images. Phantom experiments were conducted to validate the performance of using the optimal artificial <span class="hlt">noise</span> <span class="hlt">level</span> suggested by the simulation results to suppress the Nakagami artifacts by the NCA. The simulation results indicated that the artifacts of the Nakagami image in the anechoic regions can be gradually suppressed by increasing the artificial <span class="hlt">noise</span> <span class="hlt">level</span> used in the NCA to improve the image contrast-to-<span class="hlt">noise</span> ratio (CNR). The CNR of the Nakagami image reached 20 dB when the artificial <span class="hlt">noise</span> <span class="hlt">level</span> was 0.7-fold of the intrinsic <span class="hlt">noise</span> amplitude. This criterion was demonstrated by the phantom results to provide the NCA with an excellent ability to obtain artifact-free Nakagami images.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920005565','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920005565"><span>Design and performance of duct <span class="hlt">acoustic</span> treatment</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Motsinger, R. E.; Kraft, R. E.</p> <p>1991-01-01</p> <p>The procedure for designing <span class="hlt">acoustic</span> treatment panels used to line the walls of aircraft engine ducts and for estimating the resulting suppression of turbofan engine duct <span class="hlt">noise</span> is discussed. This procedure is intended to be used for estimating <span class="hlt">noise</span> suppression of existing designs or for designing new <span class="hlt">acoustic</span> treatment panels and duct configurations to achieve desired suppression <span class="hlt">levels</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20060049123','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20060049123"><span>Analysis of <span class="hlt">Acoustic</span> Modeling and Sound Propagation in Aircraft <span class="hlt">Noise</span> Prediction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Plotkin, Kenneth J.; Shepherd, Kevin P. (Technical Monitor)</p> <p>2006-01-01</p> <p>An analysis has been performed of measured and predicted aircraft <span class="hlt">noise</span> <span class="hlt">levels</span> around Denver International Airport. A detailed examination was made of 90 straight-out departures that yielded good measurements on multiple monitors. Predictions were made with INM 5, INM 6 and the simulation model NMSIM. Predictions were consistently lower than measurements, less so for the simulation model than for the integrated models. Lateral directivity ("installation effect") patterns were seen which are consistent with other recent measurements. Atmospheric absorption was determined to be a significant factor in the underprediction. Calculations of atmospheric attenuation were made over a full year of upper air data at seven locations across the United States. It was found that temperature/humidity effects could cause variations of up to +/-4 dB, depending on season, for the sites examined. It was concluded that local temperature and humidity should be accounted for in aircraft <span class="hlt">noise</span> modeling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960003376','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960003376"><span>Active Control of Fan <span class="hlt">Noise</span>-Feasibility Study. Volume 2: Canceling <span class="hlt">Noise</span> Source-Design of an <span class="hlt">Acoustic</span> Plate Radiator Using Piezoceramic Actuators</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pla, F. G.; Rajiyah, H.</p> <p>1995-01-01</p> <p>The feasibility of using <span class="hlt">acoustic</span> plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan <span class="hlt">noise</span> is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy <span class="hlt">acoustic</span> plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of <span class="hlt">acoustic</span> plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable <span class="hlt">acoustic</span> source for active control of aircraft engine fan <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890053678&hterms=acoustic+reduction+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dacoustic%2Breduction%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890053678&hterms=acoustic+reduction+noise&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dacoustic%2Breduction%2Bnoise"><span>NASA/AHS rotorcraft <span class="hlt">noise</span> reduction program - NASA Langley <span class="hlt">Acoustics</span> Division contributions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Martin, Ruth M.</p> <p>1989-01-01</p> <p>An account is given of the contributions made by NASA-Langley's rotorcraft <span class="hlt">noise</span> research programs over the last five years. Attention has been given to the broadband and blade-vortex interaction <span class="hlt">noise</span> sources; both analytical and empirical <span class="hlt">noise</span>-prediction codes have been developed and validated for several rotor <span class="hlt">noise</span> sources, and the 'Rotonet' comprehensive system-<span class="hlt">noise</span> prediction capability has been instituted. Among the technologies explored for helicopter <span class="hlt">noise</span> reduction have been higher harmonic control and active vibration-suppression.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2894914','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2894914"><span>Your attention please: increasing ambient <span class="hlt">noise</span> <span class="hlt">levels</span> elicits a change in communication behaviour in humpback whales (Megaptera novaeangliae)</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Dunlop, Rebecca A.; Cato, Douglas H.; Noad, Michael J.</p> <p>2010-01-01</p> <p>High background <span class="hlt">noise</span> is an important obstacle in successful signal detection and perception of an intended <span class="hlt">acoustic</span> signal. To overcome this problem, many animals modify their <span class="hlt">acoustic</span> signal by increasing the repetition rate, duration, amplitude or frequency range of the signal. An alternative method to ensure successful signal reception, yet to be tested in animals, involves the use of two different types of signal, where one signal type may enhance the other in periods of high background <span class="hlt">noise</span>. Humpback whale communication signals comprise two different types: vocal signals, and surface-generated signals such as ‘breaching’ or ‘pectoral slapping’. We found that humpback whales gradually switched from primarily vocal to primarily surface-generated communication in increasing wind speeds and background <span class="hlt">noise</span> <span class="hlt">levels</span>, though kept both signal types in their repertoire. Vocal signals have the advantage of having higher information content but may have the disadvantage of loosing this information in a noisy environment. Surface-generated sounds have energy distributed over a greater frequency range and may be less likely to become confused in periods of high wind-generated <span class="hlt">noise</span> but have less information content when compared with vocal sounds. Therefore, surface-generated sounds may improve detection or enhance the perception of vocal signals in a noisy environment. PMID:20392731</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150014241','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150014241"><span>Near-Field <span class="hlt">Acoustic</span> Power <span class="hlt">Level</span> Analysis of F31/A31 Open Rotor Model at Simulated Cruise Conditions, Technical Report II</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sree, Dave</p> <p>2015-01-01</p> <p>Near-field <span class="hlt">acoustic</span> power <span class="hlt">level</span> analysis of F31A31 open rotor model has been performed to determine its <span class="hlt">noise</span> characteristics at simulated cruise flight conditions. The non-proprietary parts of the test data obtained from experiments in the 8x6 supersonic wind tunnel were provided by NASA-Glenn Research Center. The tone and broadband components of total <span class="hlt">noise</span> have been separated from raw test data by using a new data analysis tool. Results in terms of sound pressure <span class="hlt">levels</span>, <span class="hlt">acoustic</span> power <span class="hlt">levels</span>, and their variations with rotor speed, freestream Mach number, and input shaft power, with different blade-pitch setting angles at simulated cruise flight conditions, are presented and discussed. Empirical equations relating models <span class="hlt">acoustic</span> power <span class="hlt">level</span> and input shaft power have been developed. The near-field <span class="hlt">acoustic</span> efficiency of the model at simulated cruise conditions is also determined. It is hoped that the results presented in this work will serve as a database for comparison and improvement of other open rotor blade designs and also for validating open rotor <span class="hlt">noise</span> prediction codes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18729653','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18729653"><span>Discrimination of <span class="hlt">acoustic</span> communication signals by grasshoppers (Chorthippus biguttulus): temporal resolution, temporal integration, and the impact of intrinsic <span class="hlt">noise</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ronacher, Bernhard; Wohlgemuth, Sandra; Vogel, Astrid; Krahe, Rüdiger</p> <p>2008-08-01</p> <p>A characteristic feature of hearing systems is their ability to resolve both fast and subtle amplitude modulations of <span class="hlt">acoustic</span> signals. This applies also to grasshoppers, which for mate identification rely mainly on the characteristic temporal patterns of their communication signals. Usually the signals arriving at a receiver are contaminated by various kinds of <span class="hlt">noise</span>. In addition to extrinsic <span class="hlt">noise</span>, intrinsic <span class="hlt">noise</span> caused by stochastic processes within the nervous system contributes to making signal recognition a difficult task. The authors asked to what degree intrinsic <span class="hlt">noise</span> affects temporal resolution and, particularly, the discrimination of similar <span class="hlt">acoustic</span> signals. This study aims at exploring the neuronal basis for sexual selection, which depends on exploiting subtle differences between basically similar signals. Applying a metric, by which the similarities of spike trains can be assessed, the authors investigated how well the communication signals of different individuals of the same species could be discriminated and correctly classified based on the responses of auditory neurons. This spike train metric yields clues to the optimal temporal resolution with which spike trains should be evaluated.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4767928','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4767928"><span>Type of Speech Material Affects Acceptable <span class="hlt">Noise</span> <span class="hlt">Level</span> Test Outcome</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Koch, Xaver; Dingemanse, Gertjan; Goedegebure, André; Janse, Esther</p> <p>2016-01-01</p> <p>The acceptable <span class="hlt">noise</span> <span class="hlt">level</span> (ANL) test, in which individuals indicate what <span class="hlt">level</span> of <span class="hlt">noise</span> they are willing to put up with while following speech, has been used to guide hearing aid fitting decisions and has been found to relate to prospective hearing aid use. Unlike objective measures of speech perception ability, ANL outcome is not related to individual hearing loss or age, but rather reflects an individual’s inherent acceptance of competing <span class="hlt">noise</span> while listening to speech. As such, the measure may predict aspects of hearing aid success. Crucially, however, recent studies have questioned its repeatability (test–retest reliability). The first question for this study was whether the inconsistent results regarding the repeatability of the ANL test may be due to differences in speech material types used in previous studies. Second, it is unclear whether meaningfulness and semantic coherence of the speech modify ANL outcome. To investigate these questions, we compared ANLs obtained with three types of materials: the International Speech Test Signal (ISTS), which is non-meaningful and semantically non-coherent by definition, passages consisting of concatenated meaningful standard audiology sentences, and longer fragments taken from conversational speech. We included conversational speech as this type of speech material is most representative of everyday listening. Additionally, we investigated whether ANL outcomes, obtained with these three different speech materials, were associated with self-reported limitations due to hearing problems and listening effort in everyday life, as assessed by a questionnaire. ANL data were collected for 57 relatively good-hearing adult participants with an age range representative for hearing aid users. Results showed that meaningfulness, but not semantic coherence of the speech material affected ANL. Less <span class="hlt">noise</span> was accepted for the non-meaningful ISTS signal than for the meaningful speech materials. ANL repeatability was comparable</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15898619','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15898619"><span>Design and optimization of a <span class="hlt">noise</span> reduction system for infrasonic measurements using elements with low <span class="hlt">acoustic</span> impedance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Alcoverro, Benoit; Le Pichon, Alexis</p> <p>2005-04-01</p> <p>The implementation of the infrasound network of the International Monitoring System (IMS) for the enforcement of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) increases the effort in the design of suitable <span class="hlt">noise</span> reducer systems. In this paper we present a new design consisting of low impedance elements. The dimensioning and the optimization of this discrete mechanical system are based on numerical simulations, including a complete electroacoustical modeling and a realistic wind-<span class="hlt">noise</span> model. The frequency response and the <span class="hlt">noise</span> reduction obtained for a given wind speed are compared to statistical <span class="hlt">noise</span> measurements in the [0.02-4] Hz frequency band. The effects of the constructive parameters-the length of the pipes, inner diameters, summing volume, and number of air inlets-are investigated through a parametric study. The studied system consists of 32 air inlets distributed along an overall diameter of 16 m. Its frequency response is flat up to 4 Hz. For a 2 m/s wind speed, the maximal <span class="hlt">noise</span> reduction obtained is 15 dB between 0.5 and 4 Hz. At lower frequencies, the <span class="hlt">noise</span> reduction is improved by the use of a system of larger diameter. The main drawback is the high-frequency limitation introduced by <span class="hlt">acoustical</span> resonances inside the pipes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OptLE..79...61B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OptLE..79...61B"><span>Determination of hydrocarbon <span class="hlt">levels</span> in water via laser-induced <span class="hlt">acoustics</span> wave</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bidin, Noriah; Hossenian, Raheleh; Duralim, Maisarah; Krishnan, Ganesan; Marsin, Faridah Mohd; Nughro, Waskito; Zainal, Jasman</p> <p>2016-04-01</p> <p>Hydrocarbon contamination in water is a major environmental concern in terms of foreseen collapse of the natural ecosystem. Hydrocarbon <span class="hlt">level</span> in water was determined by generating <span class="hlt">acoustic</span> wave via an innovative laser-induced breakdown in conjunction with high-speed photographic coupling with piezoelectric transducer to trace <span class="hlt">acoustic</span> wave propagation. A Q-switched Nd:YAG (40 mJ) was focused in cuvette-filled hydrocarbon solution at various concentrations (0-2000 ppm) to induce optical breakdown, shock wave generation and later <span class="hlt">acoustic</span> wave propagation. A nitro-dye (ND) laser (10 mJ) was used as a flash to illuminate and frozen the <span class="hlt">acoustic</span> wave propagation. Lasers were synchronised using a digital delay generator. The image of <span class="hlt">acoustic</span> waves was grabbed and recorded via charged couple device (CCD) video camera at the speed of 30 frames/second with the aid of Matrox software version 9. The optical delay (0.8-10.0 μs) between the <span class="hlt">acoustic</span> wave formation and its frozen time is recorded through photodetectors. A piezo-electric transducer (PZT) was used to trace the <span class="hlt">acoustic</span> wave (sound signal), which cascades to a digital oscilloscope. The <span class="hlt">acoustic</span> speed is calculated from the ratio of <span class="hlt">acoustic</span> wave radius (1-8 mm) and optical time delay. <span class="hlt">Acoustic</span> wave speed is found to linearly increase with hydrocarbon concentrations. The <span class="hlt">acoustic</span> signal generation at higher hydrocarbon <span class="hlt">levels</span> in water is attributed to supplementary mass transfer and impact on the probe. Integrated high-speed photography with transducer detection system authenticated that the signals indeed emerged from the laser-induced <span class="hlt">acoustic</span> wave instead of photothermal processes. It is established that the <span class="hlt">acoustic</span> wave speed in water is used as a fingerprint to detect the hydrocarbon <span class="hlt">levels</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150010438','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150010438"><span>International Space Station <span class="hlt">Acoustics</span> - A Status Report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allen, Christopher S.</p> <p>2015-01-01</p> <p>It is important to control <span class="hlt">acoustic</span> <span class="hlt">noise</span> aboard the International Space Station (ISS) to provide a satisfactory environment for voice communications, crew productivity, alarm audibility, and restful sleep, and to minimize the risk for temporary and permanent hearing loss. <span class="hlt">Acoustic</span> monitoring is an important part of the <span class="hlt">noise</span> control process on ISS, providing critical data for trend analysis, <span class="hlt">noise</span> exposure analysis, validation of <span class="hlt">acoustic</span> analyses and predictions, and to provide strong evidence for ensuring crew health and safety, thus allowing Flight Certification. To this purpose, sound <span class="hlt">level</span> meter (SLM) measurements and <span class="hlt">acoustic</span> <span class="hlt">noise</span> dosimetry are routinely performed. And since the primary <span class="hlt">noise</span> sources on ISS include the environmental control and life support system (fans and airflow) and active thermal control system (pumps and water flow), <span class="hlt">acoustic</span> monitoring will reveal changes in hardware <span class="hlt">noise</span> emissions that may indicate system degradation or performance issues. This paper provides the current <span class="hlt">acoustic</span> <span class="hlt">levels</span> in the ISS modules and sleep stations and is an update to the status presented in 2011. Since this last status report, many payloads (science experiment hardware) have been added and a significant number of quiet ventilation fans have replaced noisier fans in the Russian Segment. Also, <span class="hlt">noise</span> mitigation efforts are planned to reduce the <span class="hlt">noise</span> <span class="hlt">levels</span> of the T2 treadmill and <span class="hlt">levels</span> in Node 3, in general. As a result, the <span class="hlt">acoustic</span> <span class="hlt">levels</span> on the ISS continue to improve.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFD.H4009W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFD.H4009W"><span>Towards a Coupled Vortex Particle and <span class="hlt">Acoustic</span> Boundary Element Solver to Predict the <span class="hlt">Noise</span> Production of Bio-Inspired Propulsion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wagenhoffer, Nathan; Moored, Keith; Jaworski, Justin</p> <p>2016-11-01</p> <p>The design of quiet and efficient bio-inspired propulsive concepts requires a rapid, unified computational framework that integrates the coupled fluid dynamics with the <span class="hlt">noise</span> generation. Such a framework is developed where the fluid motion is modeled with a two-dimensional unsteady boundary element method that includes a vortex-particle wake. The unsteady surface forces from the potential flow solver are then passed to an <span class="hlt">acoustic</span> boundary element solver to predict the radiated sound in low-Mach-number flows. The use of the boundary element method for both the hydrodynamic and <span class="hlt">acoustic</span> solvers permits dramatic computational acceleration by application of the fast multiple method. The reduced order of calculations due to the fast multipole method allows for greater spatial resolution of the vortical wake per unit of computational time. The coupled flow-<span class="hlt">acoustic</span> solver is validated against canonical vortex-sound problems. The capability of the coupled solver is demonstrated by analyzing the performance and <span class="hlt">noise</span> production of an isolated bio-inspired swimmer and of tandem swimmers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2010-title42-vol1/pdf/CFR-2010-title42-vol1-sec84-1139.pdf','CFR'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2010-title42-vol1/pdf/CFR-2010-title42-vol1-sec84-1139.pdf"><span>42 CFR 84.1139 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2010&page.go=Go">Code of Federal Regulations, 2010 CFR</a></p> <p></p> <p>2010-10-01</p> <p>... 42 Public Health 1 2010-10-01 2010-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... Efficiency Respirators and Combination Gas Masks § 84.1139 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title42-vol1/pdf/CFR-2011-title42-vol1-sec84-202.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title42-vol1/pdf/CFR-2011-title42-vol1-sec84-202.pdf"><span>42 CFR 84.202 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-10-01</p> <p>... 42 Public Health 1 2011-10-01 2011-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Chemical Cartridge Respirators § 84.202 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title42-vol1/pdf/CFR-2014-title42-vol1-sec84-140.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title42-vol1/pdf/CFR-2014-title42-vol1-sec84-140.pdf"><span>42 CFR 84.140 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-10-01</p> <p>... 42 Public Health 1 2014-10-01 2014-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Supplied-Air Respirators § 84.140 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title42-vol1/pdf/CFR-2013-title42-vol1-sec84-1139.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title42-vol1/pdf/CFR-2013-title42-vol1-sec84-1139.pdf"><span>42 CFR 84.1139 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-10-01</p> <p>... 42 Public Health 1 2013-10-01 2013-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... Efficiency Respirators and Combination Gas Masks § 84.1139 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title42-vol1/pdf/CFR-2014-title42-vol1-sec84-1139.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title42-vol1/pdf/CFR-2014-title42-vol1-sec84-1139.pdf"><span>42 CFR 84.1139 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-10-01</p> <p>... 42 Public Health 1 2014-10-01 2014-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... Efficiency Respirators and Combination Gas Masks § 84.1139 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title42-vol1/pdf/CFR-2012-title42-vol1-sec84-202.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title42-vol1/pdf/CFR-2012-title42-vol1-sec84-202.pdf"><span>42 CFR 84.202 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-10-01</p> <p>... 42 Public Health 1 2012-10-01 2012-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Chemical Cartridge Respirators § 84.202 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title42-vol1/pdf/CFR-2013-title42-vol1-sec84-140.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title42-vol1/pdf/CFR-2013-title42-vol1-sec84-140.pdf"><span>42 CFR 84.140 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-10-01</p> <p>... 42 Public Health 1 2013-10-01 2013-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Supplied-Air Respirators § 84.140 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2013-title42-vol1/pdf/CFR-2013-title42-vol1-sec84-202.pdf','CFR2013'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2013-title42-vol1/pdf/CFR-2013-title42-vol1-sec84-202.pdf"><span>42 CFR 84.202 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2013&page.go=Go">Code of Federal Regulations, 2013 CFR</a></p> <p></p> <p>2013-10-01</p> <p>... 42 Public Health 1 2013-10-01 2013-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Chemical Cartridge Respirators § 84.202 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title42-vol1/pdf/CFR-2011-title42-vol1-sec84-1139.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title42-vol1/pdf/CFR-2011-title42-vol1-sec84-1139.pdf"><span>42 CFR 84.1139 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-10-01</p> <p>... 42 Public Health 1 2011-10-01 2011-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... Efficiency Respirators and Combination Gas Masks § 84.1139 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2010-title42-vol1/pdf/CFR-2010-title42-vol1-sec84-140.pdf','CFR'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2010-title42-vol1/pdf/CFR-2010-title42-vol1-sec84-140.pdf"><span>42 CFR 84.140 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2010&page.go=Go">Code of Federal Regulations, 2010 CFR</a></p> <p></p> <p>2010-10-01</p> <p>... 42 Public Health 1 2010-10-01 2010-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Supplied-Air Respirators § 84.140 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2010-title42-vol1/pdf/CFR-2010-title42-vol1-sec84-202.pdf','CFR'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2010-title42-vol1/pdf/CFR-2010-title42-vol1-sec84-202.pdf"><span>42 CFR 84.202 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2010&page.go=Go">Code of Federal Regulations, 2010 CFR</a></p> <p></p> <p>2010-10-01</p> <p>... 42 Public Health 1 2010-10-01 2010-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Chemical Cartridge Respirators § 84.202 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2011-title42-vol1/pdf/CFR-2011-title42-vol1-sec84-140.pdf','CFR2011'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2011-title42-vol1/pdf/CFR-2011-title42-vol1-sec84-140.pdf"><span>42 CFR 84.140 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2011&page.go=Go">Code of Federal Regulations, 2011 CFR</a></p> <p></p> <p>2011-10-01</p> <p>... 42 Public Health 1 2011-10-01 2011-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Supplied-Air Respirators § 84.140 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title42-vol1/pdf/CFR-2014-title42-vol1-sec84-202.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title42-vol1/pdf/CFR-2014-title42-vol1-sec84-202.pdf"><span>42 CFR 84.202 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-10-01</p> <p>... 42 Public Health 1 2014-10-01 2014-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Chemical Cartridge Respirators § 84.202 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title42-vol1/pdf/CFR-2012-title42-vol1-sec84-140.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title42-vol1/pdf/CFR-2012-title42-vol1-sec84-140.pdf"><span>42 CFR 84.140 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-10-01</p> <p>... 42 Public Health 1 2012-10-01 2012-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... PROTECTIVE DEVICES Supplied-Air Respirators § 84.140 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title42-vol1/pdf/CFR-2012-title42-vol1-sec84-1139.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title42-vol1/pdf/CFR-2012-title42-vol1-sec84-1139.pdf"><span>42 CFR 84.1139 - Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-10-01</p> <p>... 42 Public Health 1 2012-10-01 2012-10-01 false Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets... Efficiency Respirators and Combination Gas Masks § 84.1139 Air velocity and <span class="hlt">noise</span> <span class="hlt">levels</span>; hoods and helmets; minimum requirements. <span class="hlt">Noise</span> <span class="hlt">levels</span> generated by the respirator will be measured inside the hood or...</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19820015851','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19820015851"><span>GE MOD-1 <span class="hlt">noise</span> study</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wells, R. J.</p> <p>1981-01-01</p> <p><span class="hlt">Noise</span> studies of the MOD-1 Wind Turbine Generator are summarized, and a simple mathematical <span class="hlt">noise</span> is presented which is adequate to correlate the sound <span class="hlt">levels</span> found near the machine. A simple <span class="hlt">acoustic</span> measure is suggested for use in evaluating far field sound <span class="hlt">levels</span>. Use of this measure as input to a currently available sound complaint prediction program is discussed. Results of a recent statistical survey relative to the far field variation of this <span class="hlt">acoustic</span> measure because of atmospheric effects are described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26572703','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26572703"><span>Are the <span class="hlt">noise</span> <span class="hlt">levels</span> acceptable in a built environment like Hong Kong?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>To, Wai Ming; Mak, Cheuk Ming; Chung, Wai Leung</p> <p>2015-01-01</p> <p>Governments all over the world have enacted environmental <span class="hlt">noise</span> directives and <span class="hlt">noise</span> control ordinances/acts to protect tranquility in residential areas. However, there is a lack of literature on the evaluation of whether the Acceptable <span class="hlt">Noise</span> <span class="hlt">Levels</span> (ANLs) stipulated in the directive/ordinance/act are actually achievable. The study aimed at measuring outdoor environmental <span class="hlt">noise</span> <span class="hlt">levels</span> in Hong Kong and identifying whether the measured <span class="hlt">noise</span> <span class="hlt">levels</span> are lower than the stipulated ANLs at 20 categories of residential areas. Data were gathered from a territory-wide <span class="hlt">noise</span> survey. Outdoor <span class="hlt">noise</span> measurements were conducted at 203 residential premises in urban areas, low-density residential areas, rural areas, and other areas. In total, 366 daytime hourly Leq outdoor <span class="hlt">noise</span> <span class="hlt">levels</span>, 362 nighttime hourly Leq outdoor <span class="hlt">noise</span> <span class="hlt">levels</span>, and 20 sets of daily, that is, 24 L(eq,1-)h outdoor <span class="hlt">noise</span> <span class="hlt">levels</span> were recorded. The mean daytime L(eq,1-h) values ranged 54.4-70.8 dBA, while the mean nighttime L(eq,1-h) values ranged 52.6-67.9 dBA. When the measured <span class="hlt">noise</span> <span class="hlt">levels</span> were compared with the stipulated ANLs, only three out of the 20 categories of areas had outdoor <span class="hlt">noise</span> <span class="hlt">levels</span> below ANLs during daytime. All other areas (and all areas during nighttime) were found to have outdoor <span class="hlt">noise</span> <span class="hlt">levels</span> at or above ANLs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4900474','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4900474"><span>Are the <span class="hlt">noise</span> <span class="hlt">levels</span> acceptable in a built environment like Hong Kong?</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>To, Wai Ming; Mak, Cheuk Ming; Chung, Wai Leung</p> <p>2015-01-01</p> <p>Governments all over the world have enacted environmental <span class="hlt">noise</span> directives and <span class="hlt">noise</span> control ordinances/acts to protect tranquility in residential areas. However, there is a lack of literature on the evaluation of whether the Acceptable <span class="hlt">Noise</span> <span class="hlt">Levels</span> (ANLs) stipulated in the directive/ordinance/act are actually achievable. The study aimed at measuring outdoor environmental <span class="hlt">noise</span> <span class="hlt">levels</span> in Hong Kong and identifying whether the measured <span class="hlt">noise</span> <span class="hlt">levels</span> are lower than the stipulated ANLs at 20 categories of residential areas. Data were gathered from a territory-wide <span class="hlt">noise</span> survey. Outdoor <span class="hlt">noise</span> measurements were conducted at 203 residential premises in urban areas, low-density residential areas, rural areas, and other areas. In total, 366 daytime hourly Leq outdoor <span class="hlt">noise</span> <span class="hlt">levels</span>, 362 nighttime hourly Leq outdoor <span class="hlt">noise</span> <span class="hlt">levels</span>, and 20 sets of daily, that is, 24 Leq,1-h outdoor <span class="hlt">noise</span> <span class="hlt">levels</span> were recorded. The mean daytime Leq,1-h values ranged 54.4-70.8 dBA, while the mean nighttime Leq,1-h values ranged 52.6-67.9 dBA. When the measured <span class="hlt">noise</span> <span class="hlt">levels</span> were compared with the stipulated ANLs, only three out of the 20 categories of areas had outdoor <span class="hlt">noise</span> <span class="hlt">levels</span> below ANLs during daytime. All other areas (and all areas during nighttime) were found to have outdoor <span class="hlt">noise</span> <span class="hlt">levels</span> at or above ANLs. PMID:26572703</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150021044','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150021044"><span><span class="hlt">Acoustic</span> Database for Turbofan Engine Core-<span class="hlt">Noise</span> Sources. I; Volume</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gordon, Grant</p> <p>2015-01-01</p> <p> were processed using software that accounts for the effects of convective and conductive heat transfer. The software was developed under previous NASA sponsored programs. Compensated temperature spectra and compensated time histories corresponding to the dynamic temperature of the gas stream were generated. Auto-spectral and cross-spectral analyses of the data were performed to investigate spectral features, <span class="hlt">acoustic</span> circumferential mode content, signal coherence, and time delays. The dynamic temperature data exhibit a wideband and fairly flat spectral content. The temperature spectra do not change substantially with operating speed. The pressure spectra in the combustor and ITD exhibit generally similar shapes and amplitudes, making it difficult to identify any features that suggest the presence of indirect combustion <span class="hlt">noise</span>. Cross-spectral analysis reveal a strong correlation between pressure and temperature fluctuations in the ITD, but little correlation between temperature fluctuations at the entrance of the HPT and pressure fluctuations downstream of it. Temperature fluctuations at the entrance of the low pressure turbine were an order of magnitude smaller than those at the entrance to the high pressure turbine. Time delay analysis of the temperature fluctuations in the combustor was inconclusive, perhaps due to the substantial mixing that occurs between the upstream and downstream locations. Time delay analysis of the temperature fluctuations in the ITD indicate that they convect at the mean flow speed. Analysis of the data did not reveal any convincing indications of the presence of indirect combustion <span class="hlt">noise</span>. However, this analysis has been preliminary and additional exploration of the data is recommended including the use of more sophisticated signal processing to explore subtle issues that have been revealed but which are not yet fully understood or explained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22300317','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22300317"><span>Use of co-combustion bottom ash to design an <span class="hlt">acoustic</span> absorbing material for highway <span class="hlt">noise</span> barriers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arenas, Celia; Leiva, Carlos; Vilches, Luis F.</p> <p>2013-11-15</p> <p>Highlights: • The particle size of bottom ash influenced the <span class="hlt">acoustic</span> behavior of the barrier. • The best sound absorption coefficients were measured for larger particle sizes. • The maximum <span class="hlt">noise</span> absorption is displaced to lower frequencies for higher thickness. • A <span class="hlt">noise</span> barrier was designed with better properties than commercial products. • Recycling products from bottom ash no present leaching and radioactivity problems. - Abstract: The present study aims to determine and evaluate the applicability of a new product consisting of coal bottom ash mixed with Portland cement in the application of highway <span class="hlt">noise</span> barriers. In order to effectively recycle the bottom ash, the influence of the grain particle size of bottom ash, the thickness of the panel and the combination of different layers with various particle sizes have been studied, as well as some environmental properties including leachability (EN-12457-4, NEN-7345) and radioactivity tests. Based on the obtained results, the <span class="hlt">acoustic</span> properties of the final composite material were similar or even better than those found in porous concrete used for the same application. According to this study, the material produced presented no environmental risk.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100039608','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100039608"><span>International Space Station <span class="hlt">Acoustics</span> - A Status Report</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allen, Christopher S.; Denham, Samuel A.</p> <p>2011-01-01</p> <p>It is important to control <span class="hlt">acoustic</span> <span class="hlt">noise</span> aboard the International Space Station (ISS) to provide a satisfactory environment for voice communications, crew productivity, and restful sleep, and to minimize the risk for temporary and permanent hearing loss. <span class="hlt">Acoustic</span> monitoring is an important part of the <span class="hlt">noise</span> control process on ISS, providing critical data for trend analysis, <span class="hlt">noise</span> exposure analysis, validation of <span class="hlt">acoustic</span> analysis and predictions, and to provide strong evidence for ensuring crew health and safety, thus allowing Flight Certification. To this purpose, sound <span class="hlt">level</span> meter (SLM) measurements and <span class="hlt">acoustic</span> <span class="hlt">noise</span> dosimetry are routinely performed. And since the primary <span class="hlt">noise</span> sources on ISS include the environmental control and life support system (fans and airflow) and active thermal control system (pumps and water flow), <span class="hlt">acoustic</span> monitoring will indicate changes in hardware <span class="hlt">noise</span> emissions that may indicate system degradation or performance issues. This paper provides the current <span class="hlt">acoustic</span> <span class="hlt">levels</span> in the ISS modules and sleep stations, and is an update to the status presented in 20031. Many new modules, and sleep stations have been added to the ISS since that time. In addition, <span class="hlt">noise</span> mitigation efforts have reduced <span class="hlt">noise</span> <span class="hlt">levels</span> in some areas. As a result, the <span class="hlt">acoustic</span> <span class="hlt">levels</span> on the ISS have improved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1986JSV...110..129T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986JSV...110..129T"><span>Psychophysiological <span class="hlt">acoustics</span> of indoor sound due to traffic <span class="hlt">noise</span> during sleep</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tulen, J. H. M.; Kumar, A.; Jurriëns, A. A.</p> <p>1986-10-01</p> <p>The relation between the physical characteristics of sound and an individual's perception of its as annoyance is complex and unclear. Sleep disturbance by sound is manifested in the physiological responses to the sound stimuli and the quality of sleep perceived in the morning. Both may result in deterioration of functioning during wakefulness. Therefore, psychophysiological responses to <span class="hlt">noise</span> during sleep should be studied for the evaluation of the efficacy of sound insulation. Nocturnal sleep and indoor sound <span class="hlt">level</span> were recorded in the homes of 12 subjects living along a highway with high traffic density. Double glazing sound insulation was used to create two experimental conditions: low insulation and high insulation. Twenty recordings were made per subject, ten recordings in each condition. During the nights with low insulation the quality of sleep was so low that both performance and mood were negatively affected. The enhancement of sound insulation was not effective enough to increase the restorative effects of sleep. The transient and peaky characteristics of traffic sound were also found to result in non-adaptive physiological responses during sleep. Sound insulation did have an effect on <span class="hlt">noise</span> peak characteristics such as peak <span class="hlt">level</span>, peak duration and slope. However, the number of sound peaks were found to be the same in both conditions. The relation of these sound peaks detected in the indoor recorded sound <span class="hlt">level</span> signal to characteristics of passing vehicles was established, indicating that the sound peaks causing the psychophysiological disturbances during sleep were generated by the passing vehicles. Evidence is presented to show that the reduction in sound <span class="hlt">level</span> is not a good measure of efficacy of sound insulation. The parameters of the sound peaks, as described in this paper, are a better representation of psychophysiological efficacy of sound insulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100018484','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100018484"><span><span class="hlt">Acoustic</span> Performance of Novel Fan <span class="hlt">Noise</span> Reduction Technologies for a High Bypass Model Turbofan at Simulated Flights Conditions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Elliott, David M.; Woodward, Richard P.; Podboy, Gary G.</p> <p>2010-01-01</p> <p>Two novel fan <span class="hlt">noise</span> reduction technologies, over the rotor <span class="hlt">acoustic</span> treatment and soft stator vane technologies, were tested in an ultra-high bypass ratio turbofan model in the NASA Glenn Research Center s 9- by 15-Foot Low-Speed Wind Tunnel. The performance of these technologies was compared to that of the baseline fan configuration, which did not have these technologies. Sideline <span class="hlt">acoustic</span> data and hot film flow data were acquired and are used to determine the effectiveness of the various treatments. The material used for the over the rotor treatment was foam metal and two different types were used. The soft stator vanes had several internal cavities tuned to target certain frequencies. In order to accommodate the cavities it was necessary to use a cut-on stator to demonstrate the soft vane concept.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19760055094&hterms=acoustic+reduction+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dacoustic%2Breduction%2Bnoise','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19760055094&hterms=acoustic+reduction+noise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dacoustic%2Breduction%2Bnoise"><span><span class="hlt">Noise</span> reduction as affected by the extent and distribution of <span class="hlt">acoustic</span> treatment in a turbofan engine inlet</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Minner, G. L.; Homyak, L.</p> <p>1976-01-01</p> <p>An inlet <span class="hlt">noise</span> suppressor for a TF-34 engine designed to have three <span class="hlt">acoustically</span> treated rings was tested with several different ring arrangements. The configurations included: all three rings; two outer rings; single outer ring; single intermediate ring, and finally no rings. It was expected that as rings were removed, the <span class="hlt">acoustic</span> performance would be degraded considerably. While a degradation occurred, it was not as large as predictions indicated. In fact, the prediction showed good agreement with the data only for the full-ring inlet configuration. The under-predictions which occurred with ring removal were believed a result of ignoring the presence of spinning modes which are known to damp more rapidly in cylindrical ducts than would be predicted by least attenuated mode or plane wave analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760016180','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760016180"><span><span class="hlt">Noise</span> reduction as affected by the extent and distribution of <span class="hlt">acoustic</span> treatment in a turbofan engine inlet</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Minner, G. L.; Homyak, L.</p> <p>1976-01-01</p> <p>An inlet <span class="hlt">noise</span> suppressor for a TF-34 engine designed to have three <span class="hlt">acoustically</span> treated rings was tested with several different ring arrangements. The configurations included: all three rings; two outer rings; single outer ring; single intermediate ring, and finally no rings. It was expected that as rings were removed, the <span class="hlt">acoustic</span> performance would be degraded considerably. While a degradation occurred, it was not as large as predictions indicated. The prediction showed good agreement with the data only for the full-ring inlet configuration. The underpredictions which occurred with ring removal were believed a result of ignoring the presence of spinning modes which are known to damp more rapidly in cylindrical ducts than would be predicted by least attenuated mode or plane wave analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MSSP...72..266Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MSSP...72..266Y"><span>Dual-tree complex wavelet transform and SVD based <span class="hlt">acoustic</span> <span class="hlt">noise</span> reduction and its application in leak detection for natural gas pipeline</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Xuchao; Liang, Wei; Zhang, Laibin; Jin, Hao; Qiu, Jingwei</p> <p>2016-05-01</p> <p>During the last decades, leak detection for natural gas pipeline has become one of the paramount concerns of pipeline operators and researchers across the globe. However, <span class="hlt">acoustic</span> wave method has been proved to be an effective way to identify and localize leakage for gas pipeline. Considering the fact that <span class="hlt">noises</span> inevitably exist in the <span class="hlt">acoustic</span> signals collected, <span class="hlt">noise</span> reduction should be enforced on the signals for subsequent data mining and analysis. Thus, an integrated <span class="hlt">acoustic</span> <span class="hlt">noise</span> reduction method based on DTCWT and SVD is proposed in this study. The method is put forward based on the idea that <span class="hlt">noise</span> reduction strategy should match the characteristics of the noisy signal. According to previous studies, it is known that the energy of <span class="hlt">acoustic</span> signals collected under leaking condition is mainly concentrated in low-frequency portion (0-100 Hz). And ultralow-frequency component (0-5 Hz), which is taken as the characteristic frequency band in this study, can propagate a relatively longer distance and be captured by sensors. Therefore, in order to filter the <span class="hlt">noises</span> and to reserve the characteristic frequency band, DTCWT is taken as the core to conduct multilevel decomposition and refining for <span class="hlt">acoustic</span> signals and SVD is employed to eliminate <span class="hlt">noises</span> in non-characteristic bands. Both simulation and field experiments show that DTCWT-SVD is an excellent method for <span class="hlt">acoustic</span> <span class="hlt">noise</span> reduction. At the end of this study, application in leakage localization shows that it becomes much easier and a little more accurate to estimate the location of leak hole after <span class="hlt">noise</span> reduction by DTCWT-SVD.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/874373','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/874373"><span>System and method for characterizing voiced excitations of speech and <span class="hlt">acoustic</span> signals, removing <span class="hlt">acoustic</span> <span class="hlt">noise</span> from speech, and synthesizing speech</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Burnett, Greg C.; Holzrichter, John F.; Ng, Lawrence C.</p> <p>2002-01-01</p> <p>Low power EM waves are used to detect motions of vocal tract tissues of the human speech system before, during, and after voiced speech. A voiced excitation function is derived. The excitation function provides speech production information to enhance speech characterization and to enable <span class="hlt">noise</span> removal from human speech.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/1111270','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/1111270"><span>Study of some parameters affecting <span class="hlt">noise</span> <span class="hlt">level</span> in textile spinning and weaving mills.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>el-Dakhakhny, A A; Noweir, M H; Kamel, N R</p> <p>1975-01-01</p> <p><span class="hlt">Noise</span> was evaluated in six spinning and five weaving halls located in three textile mills in Egypt. Spindle speed (rpm) and loom speed (picks per minutes) were found to be important parameters affecting the <span class="hlt">noise</span> <span class="hlt">level</span> in these mills. Reduction of the number of spinning machines to five spindles per square meter of floor area will probably bring the <span class="hlt">noise</span> <span class="hlt">level</span> below the TLV. In the weaving departments, the decrease in the number of looms will not effectively reduce the <span class="hlt">noise</span> <span class="hlt">level</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020081325','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020081325"><span><span class="hlt">Acoustic</span> and Laser Doppler Anemometer Results for Confluent, 22-Lobed, and Unique-Lobed Mixer Exhaust Systems for Subsonic Jet <span class="hlt">Noise</span> Reduction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Salikuddin, M.; Martens, S.; Shin, H.; Majjigi, R. K.; Krejsa, Gene (Technical Monitor)</p> <p>2002-01-01</p> <p>The objective of this task was to develop a design methodology and <span class="hlt">noise</span> reduction concepts for high bypass exhaust systems which could be applied to both existing production and new advanced engine designs. Special emphasis was given to engine cycles with bypass ratios in the range of 4:1 to 7:1, where jet mixing <span class="hlt">noise</span> was a primary <span class="hlt">noise</span> source at full power takeoff conditions. The goal of this effort was to develop the design methodology for mixed-flow exhaust systems and other novel <span class="hlt">noise</span> reduction concepts that would yield 3 EPNdB <span class="hlt">noise</span> reduction relative to 1992 baseline technology. Two multi-lobed mixers, a 22-lobed axisymmetric and a 21-lobed with a unique lobe, were designed. These mixers along with a confluent mixer were tested with several fan nozzles of different lengths with and without <span class="hlt">acoustic</span> treatment in GEAE's Cell 41 under the current subtask (Subtask C). In addition to the <span class="hlt">acoustic</span> and LDA tests for the model mixer exhaust systems, a semi-empirical <span class="hlt">noise</span> prediction method for mixer exhaust system is developed. Effort was also made to implement flowfield data for <span class="hlt">noise</span> prediction by utilizing MGB code. In general, this study established an aero and <span class="hlt">acoustic</span> diagnostic database to calibrate and refine current aero and <span class="hlt">acoustic</span> prediction tools.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100036690','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100036690"><span>Cabin <span class="hlt">Noise</span> Studies for the Orion Spacecraft Crew Module</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dandaroy, Indranil; Chu, S. Reynold; Larson, Lauren; Allen, Christopher S.</p> <p>2010-01-01</p> <p>Controlling cabin <span class="hlt">acoustic</span> <span class="hlt">noise</span> <span class="hlt">levels</span> in the Crew Module (CM) of the Orion spacecraft is critical for adequate speech intelligibility, to avoid fatigue and to prevent any possibility of temporary and permanent hearing loss. A vibroacoustic model of the Orion CM cabin has been developed using Statistical Energy Analysis (SEA) to assess compliance with <span class="hlt">acoustic</span> Constellation Human Systems Integration Requirements (HSIR) for the on-orbit mission phase. Cabin <span class="hlt">noise</span> in the Orion CM needs to be analyzed at the vehicle-<span class="hlt">level</span> to assess the cumulative <span class="hlt">acoustic</span> effect of various Orion systems at the crewmember's ear. The SEA model includes all major structural and <span class="hlt">acoustic</span> subsystems inside the CM including the Environmental Control and Life Support System (ECLSS), which is the primary <span class="hlt">noise</span> contributor in the cabin during the on-orbit phase. The ECLSS <span class="hlt">noise</span> sources used to excite the vehicle <span class="hlt">acoustic</span> model were derived using a combination of established empirical predictions and fan development <span class="hlt">acoustic</span> testing. Baseline <span class="hlt">noise</span> predictions were compared against <span class="hlt">acoustic</span> HSIR requirements. Key <span class="hlt">noise</span> offenders and paths were identified and ranked using <span class="hlt">noise</span> transfer path analysis. Parametric studies were conducted with various <span class="hlt">acoustic</span> treatment packages in the cabin to reduce the <span class="hlt">noise</span> <span class="hlt">levels</span> and define vehicle-<span class="hlt">level</span> mass impacts. An <span class="hlt">acoustic</span> test mockup of the CM cabin has also been developed and <span class="hlt">noise</span> treatment optimization tests were conducted to validate the results of the analyses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhyA..419..659Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhyA..419..659Z"><span>Optimising threshold <span class="hlt">levels</span> for information transmission in binary threshold networks: Independent multiplicative <span class="hlt">noise</span> on each threshold</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhou, Bingchang; McDonnell, Mark D.</p> <p>2015-02-01</p> <p>The problem of optimising the threshold <span class="hlt">levels</span> in multilevel threshold system subject to multiplicative Gaussian and uniform <span class="hlt">noise</span> is considered. Similar to previous results for additive <span class="hlt">noise</span>, we find a bifurcation phenomenon in the optimal threshold values, as the <span class="hlt">noise</span> intensity changes. This occurs when the number of threshold units is greater than one. We also study the optimal thresholds for combined additive and multiplicative Gaussian <span class="hlt">noise</span>, and find that all threshold <span class="hlt">levels</span> need to be identical to optimise the system when the additive <span class="hlt">noise</span> intensity is a constant. However, this identical value is not equal to the signal mean, unlike the case of additive <span class="hlt">noise</span>. When the multiplicative <span class="hlt">noise</span> intensity is instead held constant, the optimal threshold <span class="hlt">levels</span> are not all identical for small additive <span class="hlt">noise</span> intensity but are all equal to zero for large additive <span class="hlt">noise</span> intensity. The model and our results are potentially relevant for sensor network design and understanding neurobiological sensory neurons such as in the peripheral auditory system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890007511','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890007511"><span>NASA powered lift facility internally generated <span class="hlt">noise</span> and its transmission to the <span class="hlt">acoustic</span> far field</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huff, Ronald G.</p> <p>1988-01-01</p> <p><span class="hlt">Noise</span> tests of NASA Lewis Research Center's Powered Lift Facility (PLF) were performed to determine the frequency content of the internally generated <span class="hlt">noise</span> that reaches the far field. The sources of the internally generated <span class="hlt">noise</span> are the burner, elbows, valves, and flow turbulence. Tests over a range of nozzle pressure ratios from 1.2 to 3.5 using coherence analysis revealed that low frequency <span class="hlt">noise</span> below 1200 Hz is transmitted through the nozzle. Broad banded peaks at 240 and 640 Hz were found in the transmitted <span class="hlt">noise</span>. Aeroacoustic excitation effects are possible in this frequency range. The internal <span class="hlt">noise</span> creates a <span class="hlt">noise</span> floor that limits the amount of jet <span class="hlt">noise</span> suppression that can be measured on the PLF and similar facilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130011016','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130011016"><span><span class="hlt">Acoustics</span> Reflections of Full-Scale Rotor <span class="hlt">Noise</span> Measurements in NFAC 40- by 80-Foot Wind Tunnel</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Barbely, Natasha Lydia; Kitaplioglu, Cahit; Sim, Ben W.</p> <p>2012-01-01</p> <p>The objective of current research is to identify the extent of <span class="hlt">acoustic</span> time history distortions due to wind tunnel wall reflections. <span class="hlt">Acoustic</span> measurements from the recent full-scale Boeing-SMART rotor test (Fig. 2) will be used to illustrate the quality of <span class="hlt">noise</span> measurement in the NFAC 40- by 80-Foot Wind Tunnel test section. Results will be compared to PSU-WOPWOP predictions obtained with and without adjustments due to sound reflections off wind tunnel walls. Present research assumes a rectangular enclosure as shown in Fig. 3a. The Method of Mirror Images7 is used to account for reflection sources and their <span class="hlt">acoustic</span> paths by introducing mirror images of the rotor (i.e. <span class="hlt">acoustic</span> source), at each and every wall surface, to enforce a no-flow boundary condition at the position of the physical walls (Fig. 3b). While conventional approach evaluates the "combined" <span class="hlt">noise</span> from both the source and image rotor at a single microphone position, an alternative approach is used to simplify implementation of PSU-WOPWOP for this reflection analysis. Here, an "equivalent" microphone position is defined with respect to the source rotor for each mirror image that effectively renders the reflection analysis to be a one rotor, multiple microphones problem. This alternative approach has the advantage of allowing each individual "equivalent" microphone, representing the reflection pulse from the associated wall surface, to be adjusted by the panel absorption coefficient illustrated in Fig. 1a. Note that the presence of parallel wall surfaces requires an infinite number of mirror images (Fig. 3c) to satisfy the no-flow boundary conditions. In the present analysis, up to four mirror images (per wall surface) are accounted to achieve convergence in the predicted time histories</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......195P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......195P"><span>Designing <span class="hlt">acoustics</span> for linguistically diverse classrooms: Effects of background <span class="hlt">noise</span>, reverberation and talker foreign accent on speech comprehension by native and non-native English-speaking listeners</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peng, Zhao Ellen</p> <p></p> <p>The current classroom <span class="hlt">acoustics</span> standard (ANSI S12.60-2010) recommends core learning spaces not to exceed background <span class="hlt">noise</span> <span class="hlt">level</span> (BNL) of 35 dBA and reverberation time (RT) of 0.6 second, based on speech intelligibility performance mainly by the native English-speaking population. Existing literature has not correlated these recommended values well with student learning outcomes. With a growing population of non-native English speakers in American classrooms, the special needs for perceiving degraded speech among non-native listeners, either due to realistic room <span class="hlt">acoustics</span> or talker foreign accent, have not been addressed in the current standard. This research seeks to investigate the effects of BNL and RT on the comprehension of English speech from native English and native Mandarin Chinese talkers as perceived by native and non-native English listeners, and to provide <span class="hlt">acoustic</span> design guidelines to supplement the existing standard. This dissertation presents two studies on the effects of RT and BNL on more realistic classroom learning experiences. How do native and non-native English-speaking listeners perform on speech comprehension tasks under adverse <span class="hlt">acoustic</span> conditions, if the English speech is produced by talkers of native English (Study 1) versus native Mandarin Chinese (Study 2)? Speech comprehension materials were played back in a listening chamber to individual listeners: native and non-native English-speaking in Study 1; native English, native Mandarin Chinese, and other non-native English-speaking in Study 2. Each listener was screened for baseline English proficiency <span class="hlt">level</span>, and completed dual tasks simultaneously involving speech comprehension and adaptive dot-tracing under 15 <span class="hlt">acoustic</span> conditions, comprised of three BNL conditions (RC-30, 40, and 50) and five RT scenarios (0.4 to 1.2 seconds). The results show that BNL and RT negatively affect both objective performance and subjective perception of speech comprehension, more severely for non</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002ASAJ..112R2235M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002ASAJ..112R2235M"><span>Education in <span class="hlt">acoustics</span> in Argentina</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miyara, Federico</p> <p>2002-11-01</p> <p>Over the last decades, education in <span class="hlt">acoustics</span> (EA) in Argentina has experienced ups and downs due to economic and political issues interfering with long term projects. Unlike other countries, like Chile, where EA has reached maturity in spite of the <span class="hlt">acoustical</span> industry having shown little development, Argentina has several well-established manufacturers of <span class="hlt">acoustic</span> materials and equipment but no specific career with a major in <span class="hlt">acoustics</span>. At the university <span class="hlt">level</span>, <span class="hlt">acoustics</span> is taught as a complementary--often elective--course for careers such as architecture, communication engineering, or music. In spite of this there are several research centers with programs covering environmental and community <span class="hlt">noise</span>, effects of <span class="hlt">noise</span> on man, <span class="hlt">acoustic</span> signal processing, musical <span class="hlt">acoustics</span> and <span class="hlt">acoustic</span> emission, and several national and international meetings are held each year in which results are communicated and discussed. Several books on a variety of topics such as sound system, architectural <span class="hlt">acoustics</span>, and <span class="hlt">noise</span> control have been published as well. Another chapter in EA is technical and vocational education, ranging between secondary and postsecondary <span class="hlt">levels</span>, with technical training on sound system operation or design. Over the last years there have been several attempts to implement master degrees in <span class="hlt">acoustics</span> or audio engineering, with little or no success.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GeoJI.180..883V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GeoJI.180..883V"><span>Application of <span class="hlt">acoustic</span> <span class="hlt">noise</span> and self-potential localization techniques to a buried hydrothermal vent (Waimangu Old Geyser site, New Zealand)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vandemeulebrouck, J.; Roux, P.; Gouédard, P.; Legaz, A.; Revil, A.; Hurst, A. W.; Bolève, A.; Jardani, A.</p> <p>2010-02-01</p> <p>A seismo-<span class="hlt">acoustic</span> and self-potential survey has been performed in the hydrothermal area of the old Waimangu Geyser (New Zealand), which was violently erupting a century ago. Nowadays, no surface activity is visible there. We set-up an array of 16 geophones and recorded a high and steady <span class="hlt">acoustic</span> ambient <span class="hlt">noise</span>. We applied the matched field processing (MFP) approach to the <span class="hlt">acoustic</span> data to locate the sources responsible for the ambient <span class="hlt">noise</span>. The white <span class="hlt">noise</span> constraint processor reveals the presence of a unique and well-focused <span class="hlt">acoustic</span> source at a depth of 1.5 m below the seismic array. For this very shallow source, the application of MFP enabled the determination of both the source location and the dispersion curve of seismic velocity. The study was completed by self-potential (SP) measurements on several profiles around the <span class="hlt">acoustic</span> <span class="hlt">noise</span> source, which displayed a large positive anomaly above it. The results of the SP inversion gave an electric streaming current density source very close to the <span class="hlt">acoustic</span> one. Both sources likely belong to a shallow hydrothermal structure interpreted as a small convective cell of boiling water beneath an impermeable layer. The joint application of these methods is a promising technique to recognize hydrothermal structures and to study their dynamics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/7785930','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/7785930"><span>[Clinical development of acute <span class="hlt">noise</span>-induced <span class="hlt">acoustic</span> trauma. An evaluation of a study of 250 cases].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Suc, B; Poulet, M; Asperge, A; Vix, J; Barberot, J P; Doucet, F</p> <p>1994-01-01</p> <p>Traumatic damage on Cochlea (250 cases) induced by assault gun (F.A.M.A.S.) consists in tinitus and hearing impairement on 6000 Hz. <span class="hlt">Noise</span>'s effects are specific to one Cochlea. Dissociated developments of both tinitus and hearing loss show that their anatomical sites are different. <span class="hlt">Acoustic</span> injury entails definitive haire cells lesions, cellular biochemical and vascular changes. The treatment that reestablishes or raises cochlear blood flow entails recovery in 80% of cases provided that it is given within 48 hours after the trauma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5381195','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5381195"><span>Offshore exposure experiments on cuttlefish indicate received sound pressure and particle motion <span class="hlt">levels</span> associated with <span class="hlt">acoustic</span> trauma</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Solé, Marta; Sigray, Peter; Lenoir, Marc; van der Schaar, Mike; Lalander, Emilia; André, Michel</p> <p>2017-01-01</p> <p>Recent findings on cephalopods in laboratory conditions showed that exposure to artificial <span class="hlt">noise</span> had a direct consequence on the statocyst, sensory organs, which are responsible for their equilibrium and movements in the water column. The question remained about the contribution of the consequent near-field particle motion influence from the tank walls, to the triggering of the trauma. Offshore <span class="hlt">noise</span> controlled exposure experiments (CEE) on common cuttlefish (Sepia officinalis), were conducted at three different depths and distances from the source and particle motion and sound pressure measurements were performed at each location. Scanning electron microscopy (SEM) revealed injuries in statocysts, which severity was quantified and found to be proportional to the distance to the transducer. These findings are the first evidence of cephalopods sensitivity to anthropogenic <span class="hlt">noise</span> sources in their natural habitat. From the measured received power spectrum of the sweep, it was possible to determine that the animals were exposed at <span class="hlt">levels</span> ranging from 139 to 142 dB re 1 μPa2 and from 139 to 141 dB re 1 μPa2, at 1/3 octave bands centred at 315 Hz and 400 Hz, respectively. These results could therefore be considered a coherent threshold estimation of <span class="hlt">noise</span> <span class="hlt">levels</span> that can trigger <span class="hlt">acoustic</span> trauma in cephalopods. PMID:28378762</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28378762','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28378762"><span>Offshore exposure experiments on cuttlefish indicate received sound pressure and particle motion <span class="hlt">levels</span> associated with <span class="hlt">acoustic</span> trauma.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Solé, Marta; Sigray, Peter; Lenoir, Marc; van der Schaar, Mike; Lalander, Emilia; André, Michel</p> <p>2017-04-05</p> <p>Recent findings on cephalopods in laboratory conditions showed that exposure to artificial <span class="hlt">noise</span> had a direct consequence on the statocyst, sensory organs, which are responsible for their equilibrium and movements in the water column. The question remained about the contribution of the consequent near-field particle motion influence from the tank walls, to the triggering of the trauma. Offshore <span class="hlt">noise</span> controlled exposure experiments (CEE) on common cuttlefish (Sepia officinalis), were conducted at three different depths and distances from the source and particle motion and sound pressure measurements were performed at each location. Scanning electron microscopy (SEM) revealed injuries in statocysts, which severity was quantified and found to be proportional to the distance to the transducer. These findings are the first evidence of cephalopods sensitivity to anthropogenic <span class="hlt">noise</span> sources in their natural habitat. From the measured received power spectrum of the sweep, it was possible to determine that the animals were exposed at <span class="hlt">levels</span> ranging from 139 to 142 dB re 1 μPa(2) and from 139 to 141 dB re 1 μPa(2), at 1/3 octave bands centred at 315 Hz and 400 Hz, respectively. These results could therefore be considered a coherent threshold estimation of <span class="hlt">noise</span> <span class="hlt">levels</span> that can trigger <span class="hlt">acoustic</span> trauma in cephalopods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007MeScT..18.2131T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007MeScT..18.2131T"><span>Combustion <span class="hlt">noise</span> <span class="hlt">level</span> assessment in direct injection Diesel engines by means of in-cylinder pressure components</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Torregrosa, A. J.; Broatch, A.; Martín, J.; Monelletta, L.</p> <p>2007-07-01</p> <p>The low consumption achievable with Diesel engines and the subsequent reduction of CO2 emissions, together with the new technologies allowing to meet present and future legislation for pollutant emission reduction, make them attractive from an environmental viewpoint. However, current and future Diesel concepts are intrinsically noisy, and thus in the past few years, combustion <span class="hlt">noise</span> was considered as an additional factor in engine development alongside performance, emissions and driveability. Otherwise, due to this negative issue intrinsic to Diesel combustion, end-users could be reluctant to drive Diesel-powered vehicles and their potential for environment preservation could thus be lost or underused. Evaluation procedures are then required, both for <span class="hlt">noise</span> <span class="hlt">level</span> and sound quality, that may be integrated into the global engine development process, avoiding the need to resort to long and expensive <span class="hlt">acoustic</span> tests. In this paper, such a procedure, based on the <span class="hlt">noise</span> source diagnostic through the definition of suitable components extracted from in-cylinder pressure, is proposed and validated. An innovative decomposition of the in-cylinder pressure signal is used to obtain such components, so that features associated with the excitation inside the cylinder may be properly identified. These combustion components, significant of the rate of heat release in the cylinder and the resonance in the combustion chamber, may be correlated with the overall <span class="hlt">noise</span> <span class="hlt">level</span>. A prediction of the radiated engine <span class="hlt">noise</span> <span class="hlt">level</span> more accurate than that obtained from the classical 'block attenuation' approach is achieved, while combustion process features related to the resulting <span class="hlt">noise</span> <span class="hlt">level</span> can be identified and thus corrective actions may be proposed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770013169','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770013169"><span>Single stage, low <span class="hlt">noise</span>, advanced technology fan. Volume 5: Fan <span class="hlt">acoustics</span>. Section 2: One-third octave data tabulations and selected narrowband traces</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jutras, R. R.</p> <p>1976-01-01</p> <p>The raw-<span class="hlt">acoustic</span> data corrected to standard day, from <span class="hlt">acoustic</span> tests performed on a 0.508-scale fan vehicle of a 111,300 newton thrust, full-size engine, which has application on an advanced transport aircraft, are presented. The single-stage advanced technology fan was designed to a pressure ratio of 1.8 at a tip speed of 503 m/sec to achieve the desired pressure ratio in a single-stage fan with low radius ratio, and to maintain adequate stall margin. The two basic approaches taken in the <span class="hlt">acoustic</span> design were: (1) minimization of <span class="hlt">noise</span> at the source, and (2) suppression of the generated <span class="hlt">noise</span> in the inlet and bypass exhaust duct. Suppression of the generated <span class="hlt">noise</span> was accomplished in the inlet through use of the hybrid concept (wall <span class="hlt">acoustic</span> treatment plus airflow acceleration suppression) and in the exhaust duct with extensive <span class="hlt">acoustic</span> treatment including a splitter. The goal of the design was attainment of twenty effective perceived <span class="hlt">noise</span> decibels. The suppression goal of FAR 36-20 was not reached, but improvements in the technology of both front and aft fan-<span class="hlt">noise</span> suppression were realized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880034970&hterms=routes+Administration&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Droutes%2BAdministration','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880034970&hterms=routes+Administration&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Droutes%2BAdministration"><span>The prediction of en route <span class="hlt">noise</span> <span class="hlt">levels</span> for a DC-9 aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Weir, Donald S.</p> <p>1988-01-01</p> <p>En route <span class="hlt">noise</span> for advanced propfan powered aircraft has become an issue of concern for the Federal Aviation Administration. The NASA Aircraft <span class="hlt">Noise</span> Prediction Program (ANOPP) is used to demonstrate the source <span class="hlt">noise</span> and propagation effects for an aircraft in <span class="hlt">level</span> flight up to 35,000 feet altitude. One-third octave band spectra of the source <span class="hlt">noise</span>, atmospheric absorption loss, and received <span class="hlt">noise</span> are presented. The predicted maximum A-weighted sound pressure <span class="hlt">level</span> is compared to measured data from the Aeronautical Research Institute of Sweden. ANOPP is shown to be an effective tool in evaluating the en route <span class="hlt">noise</span> characteristics of a DC-9 aircraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22395787','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22395787"><span>Anomalously high <span class="hlt">noise</span> <span class="hlt">levels</span> in a fibre Bragg grating semiconductor laser</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kurnosov, V D; Kurnosov, K V</p> <p>2015-01-31</p> <p>Taking into account gain nonlinearity allows one to obtain anomalously high <span class="hlt">noise</span> <span class="hlt">levels</span> in a fibre Bragg grating laser diode. This paper examines the effect of the gain nonlinearity due to spectral hole burning on <span class="hlt">noise</span> characteristics. (lasers)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870001317','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870001317"><span>Prediction of helicopter rotor discrete frequency <span class="hlt">noise</span>: A computer program incorporating realistic blade motions and advanced <span class="hlt">acoustic</span> formulation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brentner, K. S.</p> <p>1986-01-01</p> <p>A computer program has been developed at the Langley Research Center to predict the discrete frequency <span class="hlt">noise</span> of conventional and advanced helicopter rotors. The program, called WOPWOP, uses the most advanced subsonic formulation of Farassat that is less sensitive to errors and is valid for nearly all helicopter rotor geometries and flight conditions. A brief derivation of the <span class="hlt">acoustic</span> formulation is presented along with a discussion of the numerical implementation of the formulation. The computer program uses realistic helicopter blade motion and aerodynamic loadings, input by the user, for <span class="hlt">noise</span> calculation in the time domain. A detailed definition of all the input variables, default values, and output data is included. A comparison with experimental data shows good agreement between prediction and experiment; however, accurate aerodynamic loading is needed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25346184','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25346184"><span>Analysis of binary mixtures of aqueous aromatic hydrocarbons with low-phase-<span class="hlt">noise</span> shear-horizontal surface <span class="hlt">acoustic</span> wave sensors using multielectrode transducer designs.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bender, Florian; Mohler, Rachel E; Ricco, Antonio J; Josse, Fabien</p> <p>2014-11-18</p> <p>The present work investigates a compact sensor system that provides rapid, real-time, in situ measurements of the identities and concentrations of aromatic hydrocarbons at parts-per-billion concentrations in water through the combined use of kinetic and thermodynamic response parameters. The system uses shear-horizontal surface <span class="hlt">acoustic</span> wave (SH-SAW) sensors operating directly in the liquid phase. The 103 MHz SAW sensors are coated with thin sorbent polymer films to provide the appropriate limits of detection as well as partial selectivity for the analytes of interest, the BTEX compounds (benzene, toluene, ethylbenzene, and xylenes), which are common indicators of fuel and oil accidental releases in groundwater. Particular emphasis is placed on benzene, a known carcinogen and the most challenging BTEX analyte with regard to both regulated <span class="hlt">levels</span> and its solubility properties. To demonstrate the identification and quantification of individual compounds in multicomponent aqueous samples, responses to binary mixtures of benzene with toluene as well as ethylbenzene were characterized at concentrations below 1 ppm (1 mg/L). The use of both thermodynamic and kinetic (i.e., steady-state and transient) responses from a single polymer-coated SH-SAW sensor enabled identification and quantification of the two BTEX compounds in binary mixtures in aqueous solution. The signal-to-<span class="hlt">noise</span> ratio was improved, resulting in lower limits of detection and improved identification at low concentrations, by designing and implementing a type of multielectrode transducer pattern, not previously reported for chemical sensor applications. The design significantly reduces signal distortion and root-mean-square (RMS) phase <span class="hlt">noise</span> by minimizing <span class="hlt">acoustic</span> wave reflections from electrode edges, thus enabling limits of detection for BTEX analytes of 9-83 ppb (calculated from RMS <span class="hlt">noise</span>); concentrations of benzene in water as low as ~100 ppb were measured directly. Reliable quantification of BTEX</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19780005908','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19780005908"><span>Investigation of <span class="hlt">acoustic</span> properties of a rigid foam with application to <span class="hlt">noise</span> reduction in light aircraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Holmer, C. I.</p> <p>1972-01-01</p> <p>A analytic model of sound transmission into an aircraft cabin was developed as well as test procedures which appropriately rank order properties which affect sound transmission. The proposed model agrees well with available data, and reveals that the pertinent properties of an aircraft cabin for sound transmission include: stiffness of cabin walls at low frequencies (as this reflects on impedance of the walls) and cabin wall transmission loss and interior absorption at mid and high frequencies. Below 315 Hz the foam contributes substantially to wall stiffness and sound transmission loss of typical light aircraft cabin construction, and could potentially reduce cabin <span class="hlt">noise</span> <span class="hlt">levels</span> by 3-5 db in this frequency range at a cost of about 0:2 lb/sq. ft. of treated cabin area. The foam was found not to have significant sound absorbing properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MSSP...66..715N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MSSP...66..715N"><span>Potential of neuro-fuzzy methodology to estimate <span class="hlt">noise</span> <span class="hlt">level</span> of wind turbines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nikolić, Vlastimir; Petković, Dalibor; Por, Lip Yee; Shamshirband, Shahaboddin; Zamani, Mazdak; Ćojbašić, Žarko; Motamedi, Shervin</p> <p>2016-01-01</p> <p>Wind turbines <span class="hlt">noise</span> effect became large problem because of increasing of wind farms numbers since renewable energy becomes the most influential energy sources. However, wind turbine <span class="hlt">noise</span> generation and propagation is not understandable in all aspects. Mechanical <span class="hlt">noise</span> of wind turbines can be ignored since aerodynamic <span class="hlt">noise</span> of wind turbine blades is the main source of the <span class="hlt">noise</span> generation. Numerical simulations of the <span class="hlt">noise</span> effects of the wind turbine can be very challenging task. Therefore in this article soft computing method is used to evaluate <span class="hlt">noise</span> <span class="hlt">level</span> of wind turbines. The main goal of the study is to estimate wind turbine <span class="hlt">noise</span> in regard of wind speed at different heights and for different sound frequency. Adaptive neuro-fuzzy inference system (ANFIS) is used to estimate the wind turbine <span class="hlt">noise</span> <span class="hlt">levels</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25994692','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25994692"><span>Community response to <span class="hlt">noise</span> in Vietnam: exposure-response relationships based on the community tolerance <span class="hlt">level</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gjestland, Truls; Nguyen, Thu Lan; Yano, Takashi</p> <p>2015-05-01</p> <p>Social surveys on <span class="hlt">noise</span> annoyance have been conducted in five different cities in Vietnam. The surveys included both aircraft <span class="hlt">noise</span> (three airports) and road traffic <span class="hlt">noise</span> (five cities). The main objective for these studies was to establish dose-response functions that were representative for Vietnam. The results have been compared with results from similar surveys from other regions. Dose-response functions for aircraft <span class="hlt">noise</span> in Vietnam showing the percentage of highly annoyed people versus the <span class="hlt">noise</span> <span class="hlt">level</span> are nearly identical to those presented in the European <span class="hlt">Noise</span> Directive [European Commission (2002). http://ec.europa.eu/environment/<span class="hlt">noise</span>/directive.htm]. For road traffic <span class="hlt">noise</span>, however, the results indicate that people in Vietnam are more tolerant. The <span class="hlt">noise</span> <span class="hlt">levels</span> can be increased by 5-10 dB in order to have a response similar to the curve recommended by the European Commission.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930091991','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930091991"><span>Sound-<span class="hlt">Level</span> Measurements of a Light Airplane Modified to Reduce <span class="hlt">Noise</span> Reaching the Ground</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vogeley, A W</p> <p>1949-01-01</p> <p>An Army liaison-type airplane, representative of personal airplanes in the 150 to 200 horsepower class, has been modified to reduce propeller and engine <span class="hlt">noise</span> according to known principles of airplane-<span class="hlt">noise</span> reduction. <span class="hlt">Noise-level</span> measurements demonstrate that, with reference to an observer on the ground, a noisy airplane of this class can be made quiet -- perhaps more quiet than necessary. In order to avoid extreme and unnecessary modifications, acceptable <span class="hlt">noise</span> <span class="hlt">levels</span> must be determined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997JSV...202..249D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997JSV...202..249D"><span>Predictive <span class="hlt">Acoustic</span> Modelling Applied to the Control of Intake/exhaust <span class="hlt">Noise</span> of Internal Combustion Engines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davies, P. O. A. L.; Harrison, M. F.</p> <p>1997-05-01</p> <p>The application of validated <span class="hlt">acoustic</span> models to intake/exhaust system <span class="hlt">acoustic</span> design is described with reference to a sequence of specific practical examples. These include large turbocharged diesel generating sets, truck engines and high performance petrol engines. The discussion includes a comparison of frequency domain, time domain and hybrid modelling approaches to design methodology. The calculation of sound emission from open terminations is summarized in an appendix.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26729143','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26729143"><span>Annoyance from Road Traffic, Trains, Airplanes and from Total Environmental <span class="hlt">Noise</span> <span class="hlt">Levels</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ragettli, Martina S; Goudreau, Sophie; Plante, Céline; Perron, Stéphane; Fournier, Michel; Smargiassi, Audrey</p> <p>2015-12-29</p> <p>There is a lack of studies assessing the exposure-response relationship between transportation <span class="hlt">noise</span> and annoyance in North America. Our aims were to investigate the prevalence of <span class="hlt">noise</span> annoyance induced by road traffic, trains and airplanes in relation to distance to transportation <span class="hlt">noise</span> sources, and to total environmental <span class="hlt">noise</span> <span class="hlt">levels</span> in Montreal, Canada; annoyance was assessed as <span class="hlt">noise</span>-induced disturbance. A telephone-based survey among 4336 persons aged >18 years was conducted. Exposure to total environmental <span class="hlt">noise</span> (A-weighted outdoor <span class="hlt">noise</span> <span class="hlt">levels</span>-LAeq24h and day-evening-night equivalent <span class="hlt">noise</span> <span class="hlt">levels</span>-Lden) for each study participant was determined using a statistical <span class="hlt">noise</span> model (land use regression-LUR) that is based on actual outdoor <span class="hlt">noise</span> measurements. The proportion of the population annoyed by road traffic, airplane and train <span class="hlt">noise</span> was 20.1%, 13.0% and 6.1%, respectively. As the distance to major roads, railways and the Montreal International Airport increased, the percentage of people disturbed and highly disturbed due to the corresponding traffic <span class="hlt">noise</span> significantly decreased. When applying the statistical <span class="hlt">noise</span> model we found a relationship between <span class="hlt">noise</span> <span class="hlt">levels</span> and disturbance from road traffic and total environmental <span class="hlt">noise</span>, with Prevalence Proportion Ratios (PPR) for highly disturbed people of 1.10 (95% CI: 1.07-1.13) and 1.04 (1.02-1.06) per 1 dB(A) Lden, respectively. Our study provides the first comprehensive information on the relationship between transportation <span class="hlt">noise</span> <span class="hlt">levels</span> and disturbance in a Canadian city. LUR models are still in development and further studies on transportation <span class="hlt">noise</span> induced annoyance are consequently needed, especially for sources other than road traffic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970017414','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970017414"><span>Fan <span class="hlt">Noise</span> Prediction System Development: Source/Radiation Field Coupling and Workstation Conversion for the <span class="hlt">Acoustic</span> Radiation Code</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meyer, H. D.</p> <p>1993-01-01</p> <p>The <span class="hlt">Acoustic</span> Radiation Code (ARC) is a finite element program used on the IBM mainframe to predict far-field <span class="hlt">acoustic</span> radiation from a turbofan engine inlet. In this report, requirements for developers of internal aerodynamic codes regarding use of their program output an input for the ARC are discussed. More specifically, the particular input needed from the Bolt, Beranek and Newman/Pratt and Whitney (turbofan source <span class="hlt">noise</span> generation) Code (BBN/PWC) is described. In a separate analysis, a method of coupling the source and radiation models, that recognizes waves crossing the interface in both directions, has been derived. A preliminary version of the coupled code has been developed and used for initial evaluation of coupling issues. Results thus far have shown that reflection from the inlet is sufficient to indicate that full coupling of the source and radiation fields is needed for accurate <span class="hlt">noise</span> predictions ' Also, for this contract, the ARC has been modified for use on the Sun and Silicon Graphics Iris UNIX workstations. Changes and additions involved in this effort are described in an appendix.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3435993','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3435993"><span>An Intelligent Sensor Array Distributed System for Vibration Analysis and <span class="hlt">Acoustic</span> <span class="hlt">Noise</span> Characterization of a Linear Switched Reluctance Actuator</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Salvado, José; Espírito-Santo, António; Calado, Maria</p> <p>2012-01-01</p> <p>This paper proposes a distributed system for analysis and monitoring (DSAM) of vibrations and <span class="hlt">acoustic</span> <span class="hlt">noise</span>, which consists of an array of intelligent modules, sensor modules, communication bus and a host PC acting as data center. The main advantages of the DSAM are its modularity, scalability, and flexibility for use of different type of sensors/transducers, with analog or digital outputs, and for signals of different nature. Its final cost is also significantly lower than other available commercial solutions. The system is reconfigurable, can operate either with synchronous or asynchronous modes, with programmable sampling frequencies, 8-bit or 12-bit resolution and a memory buffer of 15 kbyte. It allows real-time data-acquisition for signals of different nature, in applications that require a large number of sensors, thus it is suited for monitoring of vibrations in Linear Switched Reluctance Actuators (LSRAs). The acquired data allows the full characterization of the LSRA in terms of its response to vibrations of structural origins, and the vibrations and <span class="hlt">acoustic</span> <span class="hlt">noise</span> emitted under normal operation. The DSAM can also be used for electrical machine condition monitoring, machine fault diagnosis, structural characterization and monitoring, among other applications. PMID:22969364</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750022793','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750022793"><span>Study of <span class="hlt">noise</span> sources in a subsonic fan using measured blade pressures and <span class="hlt">acoustic</span> theory</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hanson, D. B.</p> <p>1975-01-01</p> <p>Sources of <span class="hlt">noise</span> in a 1.4 m (4.6 ft) diameter subsonic tip speed propulsive fan running statically outdoors are studied using a combination of techniques. Signals measured with pressure transducers on a rotor blade are plotted in a format showing the space-time history of inlet distortion. Study of these plots visually and with statistical correlation analysis confirms that the inlet flow contains long, thin eddies of turbulence. Turbulence generated in the boundary layer of the shroud upstream of the rotor tips was not found to be an important <span class="hlt">noise</span> source. Fan <span class="hlt">noise</span> is diagnosed by computing narrowband spectra of rotor and stator sound power and comparing these with measured sound power spectra. Rotor <span class="hlt">noise</span> is computed from spectra of the measured blade pressures and stator <span class="hlt">noise</span> is computed using the author's stator <span class="hlt">noise</span> theory. It is concluded that the rotor and stator sources contribute about equally at frequencies in the vicinity of the first three harmonics of blade passing frequency. At higher frequencies, the stator contribution diminishes rapidly and the rotor/inlet turbulence mechanism dominates. Two parametric studies are performed by using the rotor <span class="hlt">noise</span> calculation procedure which was correlated with test. In the first study, the effects on <span class="hlt">noise</span> spectrum and directivity are calculated for changes in turbulence properties, rotational Mach number, number of blades, and stagger angle. In the second study the influences of design tip speed and blade number on <span class="hlt">noise</span> are evaluated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25479019','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25479019"><span>Long-term, passive exposure to non-traumatic <span class="hlt">acoustic</span> <span class="hlt">noise</span> induces neural adaptation in the adult rat medial geniculate body and auditory cortex.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lau, Condon; Zhang, Jevin W; McPherson, Bradley; Pienkowski, Martin; Wu, Ed X</p> <p>2015-02-15</p> <p>Exposure to loud sounds can lead to permanent hearing loss, i.e., the elevation of hearing thresholds. Exposure at more moderate sound pressure <span class="hlt">levels</span> (SPLs) (non-traumatic and within occupational limits) may not elevate thresholds, but could in the long-term be detrimental to speech intelligibility by altering its spectrotemporal representation in the central auditory system. In support of this, electrophysiological and behavioral changes following long-term, passive (no conditioned learning) exposure at moderate SPLs have recently been observed in adult animals. To assess the potential effects of moderately loud <span class="hlt">noise</span> on the entire auditory brain, we employed functional magnetic resonance imaging (fMRI) to study <span class="hlt">noise</span>-exposed adult rats. We find that passive, pulsed broadband <span class="hlt">noise</span> exposure for two months at 65 dB SPL leads to a decrease of the sound-evoked blood oxygenation <span class="hlt">level</span>-dependent fMRI signal in the thalamic medial geniculate body (MGB) and in the auditory cortex (AC). This points to the thalamo-cortex as the site of the neural adaptation to the moderately noisy environment. The signal reduction is statistically significant during 10 Hz pulsed <span class="hlt">acoustic</span> stimulation (MGB: p<0.05, AC: p<10(-4)), but not during 5 Hz stimulation. This indicates that <span class="hlt">noise</span> exposure has a greater effect on the processing of higher pulse rate sounds. This study has enhanced our understanding of functional changes following exposure by mapping changes across the entire auditory brain. These findings have important implications for speech processing, which depends on accurate processing of sounds with a wide spectrum of pulse rates.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/7444323','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/7444323"><span>The neonatal <span class="hlt">acoustic</span> reflex.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Weatherby, L A; Bennett, M J</p> <p>1980-01-01</p> <p>Probe tones from 220 Hz to 2 000 Hz were used to measure the static and dynamic <span class="hlt">acoustic</span> impedance of 44 neonates. <span class="hlt">Acoustic</span> reflex thresholds to broad band <span class="hlt">noise</span> were obtained from every neonate tested when employing the higher frequency probe tones. The reflex threshold <span class="hlt">levels</span> measured are similar to those of adults. The static impedance values are discussed to give a possible explanation of why reflex thresholds cannot be detected using conventional 220 Hz impedance bridges.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=DUCTS&pg=2&id=EJ627952','ERIC'); return false;" href="http://eric.ed.gov/?q=DUCTS&pg=2&id=EJ627952"><span><span class="hlt">Acoustical</span> Modifications for the Classroom.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Crandell, Carl C.; Smaldino, Joseph J.</p> <p>1999-01-01</p> <p>This article reviews procedures for evaluating, measuring, and modifying <span class="hlt">noise</span> and reverberation <span class="hlt">levels</span> in the classroom environment. Recommendations include: relocating children away from high <span class="hlt">noise</span> sources, such as fans, air conditioners, heating ducts, and faulty lighting fixtures, using sound-absorbing materials, using <span class="hlt">acoustical</span> ceiling tile…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26187519','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26187519"><span>[Equivalent continuous <span class="hlt">noise</span> <span class="hlt">level</span> in neonatal intensive care unit associated to burnout syndrome].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Garrido Galindo, A P; Camargo Caicedo, Y; Vélez-Pereira, A M</p> <p>2015-01-01</p> <p><span class="hlt">Noise</span> <span class="hlt">levels</span> in neonatal intensive care units allow the appearance of symptoms associated with burnout such as stress, irritability, fatigue and emotional instability on health care personnel. The aim of this study was to evaluate the equivalent continuous <span class="hlt">noise</span> <span class="hlt">levels</span> in the neonatal intensive care unit and compare the results with <span class="hlt">noise</span> <span class="hlt">levels</span> associated with the occurrence of burnout syndrome on the care team. Continuous sampling was conducted for 20 days using a type I sound <span class="hlt">level</span> meter on the unit. The maximum, the ninetieth percentile and the equivalent continuous <span class="hlt">noise</span> <span class="hlt">level</span> (Leq) values were recorded. <span class="hlt">Noise</span> <span class="hlt">level</span> is reported in the range of 51.4-77.6 decibels A (dBA) with an average of 64 dBA, 100.6 dBA maximum, and average background <span class="hlt">noise</span> from 57.9 dBA. <span class="hlt">Noise</span> <span class="hlt">levels</span> exceed the standards suggested for neonatal intensive care units, are close to maximum values referred for <span class="hlt">noise</span> exposure in the occupational standards and to <span class="hlt">noise</span> <span class="hlt">levels</span> associated with the onset of burnout; thus allowing to infer the probability of occurrence of high <span class="hlt">levels</span> of <span class="hlt">noise</span> present in the unit on the development of burnout in caregivers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/129600','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/129600"><span>[<span class="hlt">Noise</span> <span class="hlt">level</span> measurements of the air <span class="hlt">noise</span> during drilling and grinding on the fresh isolated temporal bone (author's transl)].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Paulsen, K; Vietor, K</p> <p>1975-10-01</p> <p>Aerial sound measurements with different drilling instruments were performed during dry running and preparations of the bone. Registered were the values of the small drilling instruments Sirona, Dentatus-Air, and Electro-Torque-Ritter. Also tested were the KaVo-Technique-machine, the Hall-machine, the Air-Orbit-turbine, and the Sirona-turbine. During dry running most of them already reached the allowed marginal value of <span class="hlt">noise</span> nuisance for the ear of 85 dB (A) at a distance of 35 cm. Only the Air-Orbit-machine showed a slightly lower value of 80 dB (A). The <span class="hlt">level</span> increases with the used handpieces. Normal handpieces 1:1 exert only a minimal influence, gear handpieces 2:1, however, markedly increase the <span class="hlt">level</span>. The verticity is of no importance in the range of normal rotations between 10,000 r/min. and 80,000 r/min. Only rotations in the lower frequency range of 2,000 r/min. markedly decrease the <span class="hlt">noise</span> <span class="hlt">level</span>. During bone drilling, the kind and size of the drilling bit have an influence on the intensity of the <span class="hlt">noise</span> <span class="hlt">level</span>. Quadruple wing milling cutters create a very high <span class="hlt">noise</span> <span class="hlt">level</span> (at a distance of 15 cm still above 110 dB [A!]), big rose cutters (R 16) create <span class="hlt">noise</span> <span class="hlt">levels</span> of 95 dB (A) and above, and only diamond round bits create less <span class="hlt">noise</span> (approximately 88 db [A]). Small drilling bits make such a faint <span class="hlt">noise</span>, that it is overroared by the drilling instrument. The turbines create only slightly higher <span class="hlt">levels</span> than during dry running. Larger drilling bits cannot be employed here on principle. Wing milling cutters can lead to persistent damages of the inner ear. The frequent use of dental drilling instruments for bone preparations can also lead to a hearing loss of the operator in the long run.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005ASAJ..117.2363S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005ASAJ..117.2363S"><span>Implications of the road traffic and aircraft <span class="hlt">noise</span> exposure and children's cognition and health (RANCH) study results for classroom <span class="hlt">acoustics</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stansfeld, Stephen A.; Clark, Charlotte</p> <p>2005-04-01</p> <p>Studies in West London have found associations between aircraft <span class="hlt">noise</span> exposure and childrens' cognitive performance. This has culminated in the RANCH Study examining exposure-effect associations between aircraft and road traffic <span class="hlt">noise</span> exposure and cognitive performance and health. The RANCH project, the largest cross-sectional study of <span class="hlt">noise</span> and childrens health, examined 2844 children, 9-10 years old, from 89 schools around three major airports: in the Netherlands, Spain and the United Kingdom. Children were selected by external aircraft and road traffic <span class="hlt">noise</span> exposure at school predicted from <span class="hlt">noise</span> contour maps, modeling and on-site measurements. A substudy indicated high internal <span class="hlt">levels</span> of <span class="hlt">noise</span> within classrooms. Schools were matched for socioeconomic position within countries. Cognitive and health outcomes were measured by standardized tests and questionnaires administered in the classroom. A parental questionnaire collected information on socioeconomic position, parental education and ethnicity. Linear exposure-effect associations were found between chronic aircraft <span class="hlt">noise</span> exposure and impairment of reading comprehension and recognition memory, maintained after adjustment for mothers education, socioeconomic factors, longstanding illness and classroom insulation. Road traffic <span class="hlt">noise</span> exposure was linearly associated with episodic memory. The implications of these results for childrens' learning environments will be discussed. [Work supported by European Community (QLRT-2000-00197) Vth framework program.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18247780','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18247780"><span>Short- and long-term changes in right whale calling behavior: the potential effects of <span class="hlt">noise</span> on <span class="hlt">acoustic</span> communication.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Parks, Susan E; Clark, C W; Tyack, P L</p> <p>2007-12-01</p> <p>The impact of anthropogenic <span class="hlt">noise</span> on marine mammals has been an area of increasing concern over the past two decades. Most low-frequency anthropogenic <span class="hlt">noise</span> in the ocean comes from commercial shipping which has contributed to an increase in ocean background <span class="hlt">noise</span> over the past 150 years. The long-term impacts of these changes on marine mammals are not well understood. This paper describes both short- and long-term behavioral changes in calls produced by the endangered North Atlantic right whale (Eubalaena glacialis) and South Atlantic right whale (Eubalaena australis) in the presence of increased low-frequency <span class="hlt">noise</span>. Right whales produce calls with a higher average fundamental frequency and they call at a lower rate in high <span class="hlt">noise</span> conditions, possibly in response to masking from low-frequency <span class="hlt">noise</span>. The long-term changes have occurred within the known lifespan of individual whales, indicating that a behavioral change, rather than selective pressure, has resulted in the observed differences. This study provides evidence of a behavioral change in sound production of right whales that is correlated with increased <span class="hlt">noise</span> <span class="hlt">levels</span> and indicates that right whales may shift call frequency to compensate for increased band-limited background <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3917637','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3917637"><span><span class="hlt">Noise</span> <span class="hlt">levels</span> in a dental teaching institute - A matter of concern!</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Singh, Simarpreet; Singh, Gurminder; Sharma, Sumit; Kaur, Amarinder</p> <p>2012-01-01</p> <p>Objective: To measure and assess the <span class="hlt">noise</span> <span class="hlt">levels</span> produced by various dental equipments in different areas of a dental institution and to recommend improvements if <span class="hlt">noise</span> <span class="hlt">levels</span> are not within permissible limits. Material and Methods: Sound <span class="hlt">levels</span> were measured at three different areas of a dental institution where learning and teaching activities are organized. The sound <span class="hlt">level</span> was measured using a sound <span class="hlt">level</span> meter known as ‘decibulolmeter’. In each area the <span class="hlt">noise</span> <span class="hlt">level</span> was assessed at two positions-one, at 6 inches from the operators ear and second, at the chairside instrument trolley. <span class="hlt">Noise</span> <span class="hlt">levels</span> were also assessed from a central location of the clinic area when multiple equipments were in operation simultaneously. Results: Dental laboratory machine, dental hand-piece, ultrasonic scalers, amalgamators, high speed evacuation, and other items produce <span class="hlt">noise</span> at different sound <span class="hlt">levels</span> which is appreciable. The <span class="hlt">noise</span> <span class="hlt">levels</span> generated varied between 72.6 dB in pre-clinics and 87.2 dB in prosthesis laboratory. The results are comparable to the results of other studies which are conducted elsewhere. Although the risk to the dentists is lesser, but damage to the hearing is possible over prolonged periods. Conclusion: Higher <span class="hlt">noise</span> <span class="hlt">levels</span> are potentially hazardous to the persons working in such environments especially in the laboratory areas where <span class="hlt">noise</span> <span class="hlt">levels</span> are exceeding the permissible limits. Key words:<span class="hlt">Noise</span> <span class="hlt">level</span>, equipment, hearing loss, risk, working areas. PMID:24558544</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5875386','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5875386"><span><span class="hlt">Acoustic</span> <span class="hlt">noise</span> associated with the MOD-1 wind turbine: its source, impact, and control</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kelley, N.D.; McKenna, H.E.; Hemphill, R.R.; Etter, C.L.; Garrelts, R.L.; Linn, N.C.</p> <p>1985-02-01</p> <p>This report summarizes extensive research by staff of the Solar Energy Research Institute and its subcontractors conducted to establish the origin and possible amelioration of <span class="hlt">acoustic</span> disturbances associated with the operation of the DOE/NASA MOD-1 wind turbine installed in 1979 near Boone, North Carolina. Results have shown that the source of this <span class="hlt">acoustic</span> annoyance was the transient, unsteady aerodynamic lift imparted to the turbine blades as they passed through the lee wakes of the large, cylindrical tower supports. Nearby residents were annoyed by the low-frequency, <span class="hlt">acoustic</span> impulses propagated into the structures in which the complainants lived. The situation was aggravated further by a complex sound propagation process controlled by terrain and atmospheric focusing. Several techniques for reducing the abrupt, unsteady blade load transients were researched and are discussed in the report.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15169372','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15169372"><span>Shot <span class="hlt">noise</span> spectrum of open dissipative quantum two-<span class="hlt">level</span> systems.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Aguado, Ramón; Brandes, Tobias</p> <p>2004-05-21</p> <p>We study the current <span class="hlt">noise</span> spectrum of qubits under transport conditions in a dissipative bosonic environment. We combine (non-)Markovian master equations with correlation functions in Laplace space to derive a <span class="hlt">noise</span> formula for both weak and strong coupling to the bath. The coherence-induced reduction of <span class="hlt">noise</span> is diminished by weak dissipation and/or a large <span class="hlt">level</span> separation (bias). For weak dissipation, we demonstrate that the dephasing and relaxation rates of the two-<span class="hlt">level</span> systems can be extracted from <span class="hlt">noise</span>. In the strong dissipation regime, the localization-delocalization transition becomes visible in the low-frequency <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19534855','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19534855"><span>Performance of different types of hearing protectors undergoing high-<span class="hlt">level</span> impulse <span class="hlt">noise</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Buck, Karl</p> <p>2009-01-01</p> <p>The paper describes the problems that may occur when hearing protectors, usually designed for industrial <span class="hlt">noise</span> environments, are used for high-<span class="hlt">level</span> impulse (weapon) <span class="hlt">noise</span>. The military impulse <span class="hlt">noise</span> environment is described, as are the different types of passive and active hearing protectors and the measurement procedures. The different mechanisms that may alter the effectiveness of the hearing protectors as well as their global efficiency when submitted to high-<span class="hlt">level</span> impulse <span class="hlt">noise</span> are presented. The paper also discusses how the performance values accessible to the user may be used in different damage risk criteria for continuous and impulse <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9473860','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9473860"><span><span class="hlt">Noise</span> <span class="hlt">levels</span> and hearing ability of female workers in a textile factory in Vietnam.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nguyen, A L; Nguyen, T C; Van, T L; Hoang, M H; Nguyen, S; Jonai, H; Villanueva, M B; Matsuda, S; Sotoyama, M; Sudo, A</p> <p>1998-01-01</p> <p><span class="hlt">Noise</span> and hearing ability profiles were determined in a textile factory in Vietnam. <span class="hlt">Noise</span> mapping done in the weaving section showed that the <span class="hlt">noise</span> <span class="hlt">levels</span> exceeded the Vietnamese standard of 90 dBA by as much as 9 dBA in some areas. Audiometric tests performed on 69 female workers from the weaving section revealed that workers with more than 10 years of <span class="hlt">noise</span> exposure had the worst hearing threshold <span class="hlt">levels</span> at 1,000 and 4,000 Hz. Similar findings were observed for workers greater than 35 years old. The 4,000 Hz notch, suggestive of exposure to intense <span class="hlt">noise</span>, was noted in the audiograms of 26 subjects.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985aimm.cong..407M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985aimm.cong..407M"><span>Use of <span class="hlt">acoustic</span> intensity measurements in the characterization of jet <span class="hlt">noise</span> sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Musafir, R. E.; Slama, J. G.; Zindeluk, M.</p> <p></p> <p>The usefulness of two-microphone <span class="hlt">acoustic</span>-intensity (AI) measurements for characterizing the <span class="hlt">acoustic</span> field of a jet flow is investigated by means of numerical simulations. The theoretical principles and data basis for the simulations are explained, and the intensity patterns generated by the simulation are presented graphically. It is found that the vector information in AI data from the near field are useful in understanding complex sources, but that far-field intensity charts cannot locate separate sources and may be misleading if not analyzed in terms of a sound physical model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA113724','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA113724"><span>Prenatal Effects of Exposure to High-<span class="hlt">Level</span> <span class="hlt">Noise</span>,</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1982-03-01</p> <p>Loyola University WILLIAM D. NEFF, Staff Advisor MILTON A. WHITCOMB, Study Director ARLYSS K. WIGGINS, Administrative Secretary vi "Ile CONTENTS...determining the fetal reaction to <span class="hlt">acoustic</span> stimulation. Act a Otolaryngol. 57:571-574. Edmonds, L.D., Layde, P.M., and Erikson , J.D. (1979). Airport</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhLA..380.1151S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhLA..380.1151S"><span>Estimating the <span class="hlt">level</span> of dynamical <span class="hlt">noise</span> in time series by using fractal dimensions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sase, Takumi; Ramírez, Jonatán Peña; Kitajo, Keiichi; Aihara, Kazuyuki; Hirata, Yoshito</p> <p>2016-03-01</p> <p>We present a method for estimating the dynamical <span class="hlt">noise</span> <span class="hlt">level</span> of a 'short' time series even if the dynamical system is unknown. The proposed method estimates the <span class="hlt">level</span> of dynamical <span class="hlt">noise</span> by calculating the fractal dimensions of the time series. Additionally, the method is applied to EEG data to demonstrate its possible effectiveness as an indicator of temporal changes in the <span class="hlt">level</span> of dynamical <span class="hlt">noise</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19750003913','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19750003913"><span><span class="hlt">Acoustic</span> attenuation design requirements established through EPNL parametric trades</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Veldman, H. F.</p> <p>1972-01-01</p> <p>An optimization procedure for the provision of an <span class="hlt">acoustic</span> lining configuration that is balanced with respect to engine performance losses and lining attenuation characteristics was established using a method which determined <span class="hlt">acoustic</span> attenuation design requirements through parametric trade studies using the subjective <span class="hlt">noise</span> unit of effective perceived <span class="hlt">noise</span> <span class="hlt">level</span> (EPNL).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19910001386','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19910001386"><span>Helicopter far-field <span class="hlt">acoustic</span> <span class="hlt">levels</span> as a function of reduced main-rotor advancing blade-tip Mach number</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mueller, Arnold W.; Smith, Charles D.; Lemasurier, Philip</p> <p>1990-01-01</p> <p>During the design of a helicopter, the weight, engine, rotor speed, and rotor geometry are given significant attention when considering the specific operations for which the helicopter will be used. However, the <span class="hlt">noise</span> radiated from the helicopter and its relationship to the design variables is currently not well modeled with only a limited set of full-scale field test data to study. In general, limited field data have shown that reduced main-rotor advancing blade-tip Mach numbers result in reduced far-field <span class="hlt">noise</span> <span class="hlt">levels</span>. The status of a recent helicopter <span class="hlt">noise</span> research project is reviewed. It is designed to provide flight experimental data which may be used to further understand helicopter main-rotor advancing blade-tip Mach number effects on far-field <span class="hlt">acoustic</span> <span class="hlt">levels</span>. Preliminary results are presented relative to tests conducted with a Sikorsky S-76A helicopter operating with both the rotor speed and the flight speed as the control variable. The rotor speed was operated within the range of 107 to 90 percent NR at nominal forward speeds of 35, 100, and 155 knots.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70026920','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70026920"><span>Ambient <span class="hlt">noise</span> <span class="hlt">levels</span> in the continental United States</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>McNamara, D.E.; Buland, R.P.</p> <p>2004-01-01</p> <p>The results of our <span class="hlt">noise</span> analysis are useful for characterizing the performance of existing broadband stations and for detecting operational problems and should be relevant to the future siting of ANSS backbone stations. The <span class="hlt">noise</span> maps at body-wave frequencies should be useful for estimating the magnitude threshold for the ANSS backbone and regional networks or conversely for optimizing the distribution of regional network stations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol1/pdf/CFR-2012-title14-vol1-sec36-1501.pdf','CFR2012'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2012-title14-vol1/pdf/CFR-2012-title14-vol1-sec36-1501.pdf"><span>14 CFR 36.1501 - Procedures, <span class="hlt">noise</span> <span class="hlt">levels</span> and other information.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2012&page.go=Go">Code of Federal Regulations, 2012 CFR</a></p> <p></p> <p>2012-01-01</p> <p>..., weights, configurations, and other information or data employed for obtaining the certified <span class="hlt">noise</span> <span class="hlt">levels</span> prescribed by this part, including equivalent procedures used for flight, testing, and analysis, must...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol1/pdf/CFR-2014-title14-vol1-sec36-1501.pdf','CFR2014'); return false;" href="https://www.gpo.gov/fdsys/pkg/CFR-2014-title14-vol1/pdf/CFR-2014-title14-vol1-sec36-1501.pdf"><span>14 CFR 36.1501 - Procedures, <span class="hlt">noise</span> <span class="hlt">levels</span> and other information.</span></a></p> <p><a target="_blank" href="http://www.gpo.gov/fdsys/browse/collectionCfr.action?selectedYearFrom=2014&page.go=Go">Code of Federal Regulations, 2014 CFR</a></p> <p></p> <p>2014-01-01</p> <p>..., weights, configurations, and other information or data employed for obtaining the certified <span class="hlt">noise</span> <span class="hlt">levels</span> prescribed by this part, including equivalent procedures used for flight, testing, and analysis, must...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA573561','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA573561"><span>Ocean Basin Impact of Ambient <span class="hlt">Noise</span> on Marine Mammal Detectability, Distribution, and <span class="hlt">Acoustic</span> Communication - YIP</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2012-09-30</p> <p><span class="hlt">acoustic</span> time series from Comprehensive Test Ban Treaty Organization (CTBTO) locations in the Indian (H08) and Pacific (H11) Oceans over the past...Mammal Commission, National Fish and Wildlife Foundation Grant No. 2010-0073-003 and the NOAA Vents Program. Antarctic data was also collected by H</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <center> <div class="footer-extlink text-muted"><small>Some links on this page may take you to non-federal websites. 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