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Proceedings of Meetings on Acoustics

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POMA - 158th Meeting Acoustical Society of America
Conference Location: San Antonio, Texas Conference Date: 26 - 30 October 2009
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Sediment shear as a perturbation in geoacoustic inversions and an explanation of the anomalous frequency dependence of the attenuation

Allan D. Pierce and William M. Carey

POMA Volume 8, pp. 005001 (May 2010); (14 pages)

Online Publication Date: May 19, 2010

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The depth-dependent shear wave speed in marine sediments is much less than both the compressional and water column sound speeds. The neglect of shear in geoacoustic inversions is usually justifiable, but at frequencies less than 300 Hz, the loss of acoustic energy from the water column because of nonreturning radiation of shear waves into the bottom dominates the loss due to the intrinsic attenuation of the sediment. To account for this in a simple manner, a perturbation theory that takes advantage of the small shear speed has been devised. A derivation from fundamental principles shows that, to a fair aproximation, the contribution of the shear waves to the apparent attenuation is linear in frequency. The intrinsic attenuation varies as the freqency squared. With an assumed shear wave speed of the order of 300 m/s, the shear wave contribution is sufficient to drop the exponent in the power law from 2 to 1.8
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
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Insertion loss: Train and light-vehicle horns and railroad-crossing sound levels

Raymond Brach and Matthew Brach

POMA Volume 8, pp. 015001 (November 2009); (17 pages)

Online Publication Date: November 27, 2009

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The study presented here focuses on two of the components of the sound transmission from the train horn to the interior of an automobile. One part of the paper is the development of a method to predict the attenuation of the sound level over the path from the train horn to the vehicle. The method is based on the classical sound decay equation (including variable directivity and theoretical 6 dB drop-off per doubling of distance) but is modified to accommodate drop-off rates based on experimentally measured values. Such values are reported in current literature to range typically between 5 and 8 dB. The second portion of the sound path covered in this paper is the attenuation of the sound level due to transmission through vehicle bodies. This attenuation is frequently described by a quantity known as insertion loss. Insertion loss values and insertion loss spectra are measured for seven different light vehicles (1998 through 2007 model years). The range of insertion loss for the seven vehicles for the conditions of a) all windows closed and b) driver's window fully open were found to be between 31 and 37 dBA and 1 and 7 dBA, respectively.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
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Uncertainty of sound power levels determined following Air Conditioning Heating and Refrigeration Institute Standard 220

Stephen Lind

POMA Volume 8, pp. 015002 (January 2010); (9 pages)

Online Publication Date: January 28, 2010

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As part of the AHRI, ASA-ANSI, and ISO standards development processes, the uncertainty of sound power measurements needs to be quantified for inclusion in sound power standards. A study of four reverberation rooms with volumes of 140, 280, 560, and 1790 cubic meters was undertaken. Sound power levels for five noise sources (two vertical shafted sound sources, two horizontal shafted sound sources, and a leaf blower) were determined using ARI Standard 220. Variables investigated include: source location, source orientation, room conditions, source operating characteristics, and microphone traverse length. The frequency range of interest was 25 Hz to 10 kHz. Measurements were repeated and the order of tests was randomized. Of particular interest was the difference between the 140 cubic foot room and the other rooms to confirm the room qualification process required by ARI Standard 220 because the 140 cubic foot room does not meet the ARI Standard 220 qualification process but does meet the requirements in ISO 3741. This work will be helpful in understanding the sources of variation and allow for a starting point for determining if improvements are needed and if so what factors should be considered.
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43.55.Cs Stationary response of rooms to noise; spatial statistics of room response; random testing
43.55.Nd Reverberation room design: theory, applications to measurements of sound absorption, transmission loss, sound power
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Studying architectural acoustics through the University of Nebraska's Architectural Engineering Program

Lily M. Wang and Siu-Kit Lau

POMA Volume 8, pp. 015003 (May 2010); (12 pages)

Online Publication Date: May 11, 2010

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Architectural Engineering (AE) is a discipline of study that is only currently available at 17 schools across the United States, and even fewer of these AE programs include acoustics as a main option in their curricula. This presentation will review the Nebraska Acoustics Group, housed within the AE Program at the University of Nebraska which began in 1998. Students may study acoustics within any of our five engineering degree programs (BSAE, MAE, MEng, MS and PhD). Currently there are two AE faculty out of 11 who focus in acoustics at Nebraska, and the program regularly offers at least six recurring acoustics courses. Descriptions of the acoustics courses, the research interests of the Nebraska Acoustics Group, and where our graduates are to date will be given. Specifically highlighted will be the theme of our acoustics group: to promote the advancement and science of architectural acoustics by closely tying our coursework and research to practice in the 'real-world'.
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43.50.Jh Noise in buildings and general machinery noise
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
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Statistical Spectrogram Modeling and Analysis for Blind Estimation of Room Acoustics from Musical Recordings

Gang Ren, Mark Bocko, and Dave Headlam

POMA Volume 8, pp. 015004 (February 2011); (10 pages)

Online Publication Date: February 11, 2011

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An algorithm employing Markov random field modeling has been applied to spectrographic representations of musical recordings to uncover acoustical features of the recording environment. For recorded music, the reverberation pattern is most visible at the onset/offset edges of harmonic components in the spectrogram. Edge features extracted through image analysis algorithms can be mapped to the acoustical features of the recording space, but the correspondence is complicated by the inherent randomness of the musical "test signal." This is exacerbated in the media production process because a final mix can be generated from separate recordings from multiple acoustic spaces. The Markov random field modeling algorithm utilizes data-modeling techniques to estimate the probabilistic links between edge analysis results and room acoustical features and further to identify the probabilistic nature of any time-variation in latent room acoustics. Our algorithm obtained enhanced room acoustics feature extraction performance by allowing a gradual refinement of the room acoustics feature vectors through dynamic fusion of prior estimates and knowledge from current musical segments. This on-line approach is also more computationally efficient compared to batch processing. Multiple variants of the proposed algorithm are demonstrated and compared to existing blind room acoustics parameter estimation methods.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Mc Room acoustics measuring instruments, computer measurement of room properties
43.60.Ac Theory of acoustic signal processing
43.60.Uv Model-based signal processing
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Time-frequency Test Signal Synthesis for Acoustic Measurements During Music Concerts

Gang Ren, Mark Bocko, and Dave Headlam

POMA Volume 8, pp. 015005 (February 2011); (12 pages)

Online Publication Date: February 11, 2011

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When occupied by an audience, a musical performance space exhibits different acoustic characteristics compared to when it is empty. To obtain acoustical measurements with an audience present would require them to sit through an entire session of acoustic test signals, which is not practical. The dynamics of room acoustics parameters during an on-going concert may also be important to the mixing and recording engineers. These acoustic measurement scenarios demand an analysis tool for performing the designated tests during music concert sessions while not being noticeable by the audience. An acoustic measurement technique employing test signals generated during a musical performance is proposed. This method employs an adaptive time-frequency synthesis algorithm that determines the energy vacancies in the spectrogram of the on-going performance and automatically generates low-energy test signals that fill in the vacancies. The energy level of the test signal can be low enough to be masked by the music while high enough to be measurable above the noise floor. Several classes of test signals are proposed and their implementations in live musical events are demonstrated. Different system identification methods for estimating architectural acoustics parameters from the recorded test signals are also discussed and compared.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Mc Room acoustics measuring instruments, computer measurement of room properties
43.58.Ta Computers and computer programs in acoustics
43.60.Hj Time-frequency signal processing, wavelets
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Robert T. Beyer: A sustained record of distinguished service to the profession

Allan D. Pierce

POMA Volume 8, pp. 025001 (May 2010); (15 pages)

Online Publication Date: May 19, 2010

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A historical and anecdotal account is given of Robert T. Beyer's professional service. Highlights include his service to the Acoustical Society as Member of the Executive Council (1956-1959), Vice-President (1961-1962), Chair of the Physical Acoustics Technical Committee (1963-1964), President-Elect (1967-1968), President (1968-1969), and Treasurer (1974-1994). He was Chair of the Investments Committee (1990-1992) and served as an Associate Editor of the Journal for three distinct terms: 1952-1955 (References), 1965-1969 (Acoustical News from Abroad), and 1985-1991 (Book Reviews). He also served as interim Editor-in-Chief after the death of Robert B. Lindsay in 1985. Beyer was a voracious reader, an indefatigable translator, and a prolific writer. He wrote several textbooks, numerous book reviews, and frequent reports in JASA on the finances of the Society. His activities as a translator and editor of translated journals are legendary. Beyer's connections with the American Institute of Physics include Board of Governors (1969), Member of Executive Committee of Board (1974), Member of Translation Advisory Board (1955-1978) and its Chairman (1957-1977), and Board of Translations Editors (1978). The ASA awarded Beyer its Distinguished Service Citation in 1978, but he undoubtedly did enough more between 1978 and 2008 to justify being awarded several additional Service Citations.
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43.10.Gi Editorials, Forum
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Why we have two ears - take two: a revised experiment on sound localization

Ralph T. Muehleisen

POMA Volume 8, pp. 025002 (July 2011); (11 pages)

Online Publication Date: July 31, 2011

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Whether they fly, swim, crawl, or walk, vertebrates have binaural auditory systems. Two ears provide redundancy in case of injury to the auditory system, improve the ability to detect quiet sounds, and perhaps most importantly, improve the ability to localize sound. A simple experiment in sound localization using headphone based auralization was presented at a previous meeting. In response to some very useful suggestions a new experiment has been developed. In this experiment, a subject sits in a chair surrounded by eight speakers placed in a circle around the subject. The tester plays a signal through one of the speakers and the subject indicates the perceived direction of sound. The tester repeats the test with several different sounds and many different directions. The experiment is repeated with one ear occluded using a high isolation insert earplug and an over the ear hearing protector. The experiment is best performed in a quiet room with few reflections.
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43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources
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The Rubens tube

Kent L. Gee

POMA Volume 8, pp. 025003 (August 2011); (9 pages)

Online Publication Date: August 21, 2011

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In 1905, Heinrich Rubens and Otto Krigar-Menzel published a paper describing a unique acoustics teaching apparatus. They developed a flammable gas-filled tube with holes in the top that revealed the acoustic standing wave behavior via the height of flames above the tube. Interestingly, their article holds the distinction of being printed immediately following Einstein's Nobel-prize winning paper on the photoelectric effect. From that auspicious beginning, the "Rubens tube" has been used for over a century in the teaching of acoustical resonance behavior. This article describes some of the history around the tube's development and its operation, as well as some of the commentary and investigations involving the flame tube found in the literature.
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43.20.Ks Standing waves, resonance, normal modes
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Time Reversal Focusing for Pipeline Structural Health Monitoring

Joel Harley, Nicholas O'Donoughue, Yuanwei Jin, and Jose M. Moura

POMA Volume 8, pp. 030001 (January 2010); (8 pages)

Online Publication Date: January 20, 2010

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This paper investigates the use of time reversal processing techniques to compensate for multimodal and dispersive effects in a low-power structural health monitoring system for pipelines. We demonstrate the use of time reversal as a pitch-catch operation between two transducer arrays to illuminate changes caused by damage on a pipe. We then show and discuss how differences in the severity of damage affect the signals recorded at the receiving transducer array and demonstrate how these results can be interpreted to measure those changes. Our results are demonstrated through experimental observation.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation
43.60.Vx Acoustic sensing and acquisition
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Squealing noise in light rail transport systems: Implications in noise mapping

Lucie Habásková and Antonio P. Carvalho

POMA Volume 8, pp. 040001 (December 2009); (16 pages)

Online Publication Date: December 04, 2009

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Squealing noise is generated by railway vehicles riding through curves having closed radius. It is a result of wheels sliding on the rail when they negotiate a curve. This kind of noise is very annoying for people living in the surrounding areas where this phenomenon occurs because it has a characteristic spectrum that is dominated by discrete frequency components. Usually, squeal noise is not correctly accounted in urban areas noise maps. This paper presents the results of field measurements of squealing noise in Porto (Portugal) where a new light-rail system is operating. The goal was to characterize the acoustic effect of this type of noise in making noise maps. With the results obtained from in situ measurements, the squealing noise was simulated using Cadna/A software. This paper compares three variants of squeal noise use and simulation with the software CADNA/A. Comparing the noise map generated using the field measurements, with maps taking no account for squealing noise, a large difference in noise levels can be found (up to 17 dBA) leading to errors up to 100 m in noise exposed areas. A correction method was found to be easily incorporated in this model to improve the noise map estimation procedure.
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43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.50.Sr Community noise, noise zoning, by-laws, and legislation
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In-situ measures of user's preferred listening levels with a portable digital music device

Edward L. Goshorn, Kathryn J. White, and Brett E. Kemker

POMA Volume 8, pp. 040002 (May 2010); (6 pages)

Online Publication Date: May 27, 2010

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The recent development and popular use of personally worn digital music devices (PDMDs) have led to concerns about the intensity levels they produce. There is concern that users will set a PDMD to levels that are known to be hazardous to human hearing. The concern stems from the private nature of a PDMD in that insert earphones are worn that restrict the output to the user's ears, thus prohibiting monitoring of such devices by parents, teachers, employers, etc. This project measured the in situ dB SPL produced by PDMDs worn by 31 young adults (18-23 years) who had been wearing PDMDs for 3 years or less. Subjects set their PDMD to their preferred listening level (PLL) for a popular tune. Once set, in situ SPL measures of the tune at a reference point and then for a white noise were obtained with a probe microphone located near the eardrum. Hearing thresholds were also obtained. Results showed a range of 52-107 dB with a mean PLL of 83 dB for music and a range of 53-99 dB with a mean PLL of 79 dB for white noise. None of the subjects had significant hearing loss.
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43.50.Hg Noise control at the ear
43.50.Qp Effects of noise on man and society
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.50.Yw Instrumentation and techniques for noise measurement and analysis
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How can a video game cause panic attacks? 1. Effects of an auditory stressor on the human brainstem

Judith Lauter, Elizabeth Mathukutty, and Brandon Scott

POMA Volume 8, pp. 050001 (November 2009); (18 pages)

Online Publication Date: November 02, 2009

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The auditory brainstem response (ABR) was recorded during simultaneous binaural presentation of two types of sounds: 1) condensation clicks presented through in-the-ear earphones at 43.1/sec, 60dB nHL; and 2) recordings of breathing sounds, presented through supra-aural headphones, at levels adjusted by participants to be equivalent to the clicks. In alternate blocks, the breathing sounds were either: 1) a recording of quiet breathing (blocks 1, 3, 5); or 2) a recording of erratic (stressed) breathing (blocks 2, 4). The erratic breathing was modeled on a video game soundtrack in which the character was represented as running, wounded, and frightened. Four 2048-sweep ABR waveforms were collected in each of the five blocks, and the mean amplitude of ABR peak V was calculated over each set of four waveforms. Results indicate a significant decrease in the amplitude of ABR peak V during erratic breathing vs. quiet breathing. Implications include: 1) new evidence of the effect of selective attention on the ABR; 2) the potential for using auditory stressors to study the central physiology of emotional responses in humans; and 3) clues to physiological correlates of the effects of certain video games known to evoke panic attacks in susceptible players.
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43.64.Qh Electrophysiology of the auditory central nervous system
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Comparison of particle filter and histogram filter performance for passive sonar localization

Colin W. Jemmott, Richard L. Culver, and Jack W. Langelaan

POMA Volume 8, pp. 055001 (December 2009); (10 pages)

Online Publication Date: December 22, 2009

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This paper compares the performance of histogram and particle filters for localizing and tracking a highly maneuvering target using two widely spaced horizontal passive sonar arrays. Both filters are numerical implementations of Bayes' filter, which use recursively estimate state vectors with nonlinear update equations and non-Gaussian prior probability density functions. The histogram filter uses a grid-based approach that is analogous to midpoint rectangular integration, while the particle filter uses a direct Monte Carlo approach. Both filters are shown to successfully track a source in an example with synthetic data given sufficient computational resources. Their performance is also compared in situations where computational power is severely restricted; then the particle filter outperforms the histogram filter in this example.
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43.60.Jn Source localization and parameter estimation
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Blind Deconvolution of Quadratic Time-Frequency Representations of Musical Signals for Reverberation Feature Extraction

Gang Ren, Mark Bocko, and Dave Headlam

POMA Volume 8, pp. 055002 (February 2011); (12 pages)

Online Publication Date: February 25, 2011

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An acoustic space is uniquely characterized by its reverberant behavior. Due to the complexity of the multiple reflections and diffraction of sound in an enclosure, currently available system identification algorithms cannot effectively estimate the impulse response of a concert hall simply from musical recordings in that space. This paper reports the use of blind image deconvolution methods to construct echo patterns from quadratic time-frequency representations of reverberant recordings of music. First, a quadratic time-frequency analysis is performed to decompose the musical signal into its constituent harmonic components. Quadratic time-frequency analysis methods are known to give enhanced resolution in the time-frequency plane in comparison to conventional Fourier analysis. Reverberant features then appear as blur in the time-frequency plane, which can be estimated by employing the methods of blind deconvolution of this "image" of the sound. The proposed algorithm retrieves both the blur pattern, which corresponds to the reverberation echogram, and the direct acoustic signal.By choosing the time-frequency frame scale and smoothing window, a multi-resolution analysis of the underlying acoustic impulse response is obtained. Various quadratic time-frequency analysis methods are evaluated and their relative performance is reported. The proposed methods are also compared to existing dereverberation algorithms.
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43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Mc Room acoustics measuring instruments, computer measurement of room properties
43.60.Ac Theory of acoustic signal processing
43.60.Hj Time-frequency signal processing, wavelets
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Identification of asynchronous monaural and dichotic vowel pairs across the adult lifespan

Daniel Fogerty, Diane Kewley-Port, and Larry Humes

POMA Volume 8, pp. 060001 (August 2010); (13 pages)

Online Publication Date: August 13, 2010

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Temporal onset asynchrony is one cue that listeners use to identify concurrent vowels. Young (N=80; 18-31 years), middle-age (N=40; 40-55 years), and older (N=150; 60-88 years) adults identified vowel pairs in a temporal-order paradigm under monaural and dichotic stimulus presentations. Experiments used forced-choice constant-stimuli methods to determine the smallest stimulus onset asynchrony (SOA) between brief 70-ms vowels that enabled identification of the stimulus sequence. Vowels modified from four words (pit, pet, pot, and put) served as stimuli. All listeners identified the vowels in isolation with better than 90% accuracy. Results indicated that older listeners performed significantly poorer on monaural and dichotic temporal-order identification tasks than young listeners, with middle-age listeners in between. Correlations of performance with age across the full age span were moderate. For all three groups, SOAs for the dichotic task were significantly longer than those for the monaural task. A significant main effect of vowel pair was observed, indicating that not all vowel pairs were equally identifiable. Patterns of vowel pair identification were similar across all groups for both monaural and dichotic presentations; however, interactions with age group were observed. Effects of vowel order and dominance were also observed.
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43.71.Lz Speech perception by the aging
43.71.Rt Sensory mechanisms in speech perception
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Noise Reduction of honeycomb sandwich panels with acoustic mesh caps.

Christina Naify, Matt Sneddon, and Steve Nutt

POMA Volume 8, pp. 065002 (November 2009); (15 pages)

Online Publication Date: November 27, 2009

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The noise reduction effectiveness of acoustic mesh septa caps in composite honeycomb sandwich panels was evaluated. The acoustic mesh in the cells acted as a lightweight resonator in weight-critical aerospace structures. Nylon mesh was inserted into they honeycomb cells of the sandwich panels and the acoustic absorption (AA) and transmission loss (TL) of the panels was measured using a normal incidence impedance tube. Single septa inserted into each cell yielded consistent improvements of 2dB in TL over low to mid-frequencies (50-1600Hz). A double layer of septa further increased these acoustic properties in the mid-frequency range by an additional 2dB. Varying the size of the mesh-weave had a significant effect. Acoustic absorption of the panels improved by a factor of 2 for the single septa and was further increased by perforating the panel facesheet. Results of the facesheet perforation were consistent with predicted values. Over low to mid-frequencies, septa yielded measurable sound-mitigating results for a small weight addition with no change to the' mechanical performance of the panels.
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43.40.At Experimental and theoretical studies of vibrating systems
43.40.Dx Vibrations of membranes and plates
43.50.Gf Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
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Nonlinear sensitivity of capacitive micromachined ultrasonic Lamb wave transducers

Li-Feng Ge

POMA Volume 8, pp. 065003 (March 2011); (7 pages)

Online Publication Date: March 12, 2011

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A capacitive micromachined ultrasonic Lamb wave transducer using the second-order bending mode of high-aspect-ratio rectangular diaphragms to excite and receive Lamb waves in a silicon plate was presented [L. Ge, SPIE 6358, 1I:1-6 (2006)]. Thus, the width of the diaphragm is made equal to the wavelength of the A0 wave, and all the transducer parameters can be determined by the TDK model for CMUTs with high-aspect-ratio rectangular diaphragms. The sensitivity, i.e., a ratio of the relative frequency shift to the change in mass loading of the plate, is derived, and is a nonlinear function, which is the same as that for capacitive ultrasonic mass resonators [L. Ge, IEEE IUS, 1034-1037 (2008)]. Also, it is a general nonlinear sensitivity expression available for both capacitive and piezoelectric gravimetric sensors. The area density increment, caused by the adsorbed or bound molecules or the fluid loading, is usually comparable with the area density of the silicon plate. Therefore, it is essential to use the nonlinear expression for determining the sensitivity accurately. The capacitive Lamb wave transducers are very attractive as gravimetric sensors for chemical and biological sensing since they have much simple structure and high sensitivity.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
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Low-frequency seismo-acoustic propagation near thin and low-shear speed ocean sediment layers

Jon M. Collis

POMA Volume 8, pp. 070001 (December 2009); (10 pages)

Online Publication Date: December 09, 2009

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Accurate and efficient prediction of propagation over realistic models of elastic ocean sediments has been achieved recently using parabolic equations. A concern has been low-shear wave speed sediments that can become singular as the wave speed tends toward zero. A historic approach for treating a sediment of this type has been to assume it is a fluid and that effects due to elasticity are negligible. This approach does not account for second order effects such as energy loss due to frequency-dependent attenuation. In addition, thin sediment layers typical of those found at the ocean bottom interface have been difficult to treat numerically. At low frequencies, layers of this type can be treated as a 'massive' interface between the water and higher-shear speed sediment basement layers. To satisfy interface conditions across the layer, Rayleigh jump conditions are imposed [F. Gilbert, Ann. Geofisica XL, 1211 (1997)]. A consequence of this approximation is that interface and other wave types become dispersive where they were not previously. In this presentation, the massive elastic interface is benchmarked with an elastic parabolic equation and the effects of resultant errors are quantified.
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43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
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Evolution of navy diver exposure standards for deterministic underwater sound in the 100-500 hertz band

Frederick M. Pestorius, Edward A. Cudahy, and David M. Fothergill

POMA Volume 8, pp. 070002 (December 2009); (8 pages)

Online Publication Date: December 09, 2009

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US Navy development of Low Frequency Active (LFA) sonar at the end of the Cold War resulted in the adverse exposure of Navy divers to high levels of LFA sound. An initial 30 month study into the effects on Navy divers of deterministic waveforms in the frequency band 160-320 HZ was conducted. Sound pressure levels up to 160 dB re 1μPa were utilized in a series of experimental observations. Auditory, animal, and human diver studies were completed. Additionally, modeling studies were conducted in the areas of cavitation, hyperthermia, tissue shearing, chest wall/lung displacement and rectified diffusion. Ultimately, 453 exposures using 87 different test subjects were conducted. These tests yielded a baseline set of guidelines for the exposure of Navy divers to deterministic sonar transmissions in the subject test band. The Navy has continued to refine and expand these guidelines to the present day utilizing both modeling and field exposure studies. A summary of the initial and subsequent testing and a tracing of the evolution of the current guidelines will be presented.
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43.80.Nd Effects of noise on animals and associated behavior, protective mechanisms
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The applicability of a small towed array system to the ocean bottom sediment classification problem.

William M. Carey and James F. Lynch

POMA Volume 8, pp. 070003 (May 2010); (11 pages)

Online Publication Date: May 19, 2010

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An autonomous array system is uniquely suited to perform near bottom ~1m ) measurements of horizontal wave number spectra that estimate water and interface wave numbers. Synthetic coherent processing provides the required gain to observe the interface wave peak ~40-50 dB below the peaks of water modes. Comparable measurements were performed with an array of seismometers (Muir et al, 1991). These spectra contain the information necessary to perform inversions that account for compressional and shear wave speed gradients. Spatial transforming the computed pressure field produces spectra comparable with measurements. Variations of the geoacoustic profiles show that the present of gradient produces additional identifiable spectral structure corresponding to shear waves trapped with in the sediments. In the experiments discussed the sound source was on the bottom and the array was towed by a vehicle. However it is feasible to either use a source of sound on the vehicle or on a companion vehicle to do surveys. This method is a fast, efficient and accurate ocean acoustic measurement tool useful in rapid waveguide characterization with the appropriate inversion technology.
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43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.30.Bp Normal mode propagation of sound in water
43.60.Gk Space-time signal processing, other than matched field processing
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Measurement of sound transmission through mud at Dodge Pond, Connecticut

William M. Carey and Allan D. Pierce

POMA Volume 8, pp. 070004 (May 2010); (8 pages)

Online Publication Date: May 19, 2010

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Depositional muddy sediments are slow bottoms and pose a problem for the sonic detection of buried ordnance. This paper addresses the question: can the frequency dependent dispersion be predicted and verified by measurements in areas where buried object detection is required? Wood and Weston (Acustica, V14, 1964) have indicated that muddy sediments in the kHz range have a compressional speed 3% less than water with a frequency dependent attenuation (less than that of sand). A theoretical treatment of "muddy sediments", the Card House Theory (Pierce and Carey, POMA (5), 7001, 2009), estimates the slow sound speed and frequency dispersion proportional to mud porosity. Preliminary Dodge Pond results obtained with a buried array (1 to 10 kHz) are presented and illustrate the importance of micro-bubbles on the dispersion characteristic. The initial measurements on the disturbed sediment were found strongly influenced by scattering from larger bubbles whereas the results after a period of 10 months showed the effect of a smaller size distribution of bubbles. Estimates of the dispersion characteristic of mud and the effect of micro-bubbles are discussed. Finally the application of an impedance tube to the characterization of mud is discussed.
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43.20.Hq Velocity and attenuation of acoustic waves
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.30.Ft Volume scattering
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
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