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Journal of the Acoustical Society of America

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Jan 2011

Volume 129, Issue 1, pp. EL1-547

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Perceptual assimilation of Dutch vowels by Peruvian Spanish listeners

Paola Escudero and Daniel Williams

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. EL1-EL7 (2011); (7 pages)

Online Publication Date: 18 Jan 2011

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Many cross-language and L2 speech perception studies have been conducted on English sounds and a limited number of speakers or synthetic tokens have been used for auditory stimuli. The Spanish listeners of the present study were presented with natural tokens of Dutch vowels produced by males and females selected from the corpus reported in Adank et al. [(2004) J. Acoust. Soc. Am. 116, 1729–1738]. The results show that single category assimilations are common and that certain Dutch vowels frequently assimilate to Spanish diphthongs. Predictions are made for Spanish learners’ initial stage in the acquisition of the Dutch vowel system.
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43.71.Hw Cross-language perception of speech
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.71.An Models and theories of speech perception
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Experimental implementation of reverse time migration for nondestructive evaluation applications

Brian E. Anderson, Michele Griffa, Pierre-Yves Le Bas, Timothy J. Ulrich, and Paul A. Johnson

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. EL8-EL14 (2011); (7 pages)

Online Publication Date: 18 Jan 2011

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Reverse time migration (RTM) is a commonly employed imaging technique in seismic applications (e.g., to image reservoirs of oil). Its standard implementation cannot account for multiple scattering/reverberation. For this reason it has not yet found application in nondestructive evaluation (NDE). This paper applies RTM imaging to NDE applications in bounded samples, where reverberation is always present. This paper presents a fully experimental implementation of RTM, whereas in seismic applications, only part of the procedure is done experimentally. A modified RTM imaging condition is able to localize scatterers and locations of disbonding. Experiments are conducted on aluminum samples with controlled scatterers.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation
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Lateralization produced by interaural intensitive disparities appears to be larger for high- vs low-frequency stimuli

Leslie R. Bernstein and Constantine Trahiotis

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. EL15-EL20 (2011); (6 pages) | Cited 1 time

Online Publication Date: 18 Jan 2011

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The purpose of this communication is to report the results of a study indicating that a given magnitude of interaural intensitive disparity (IID) produced a larger extent of laterality, as measured via an acoustic pointer, for stimuli centered at 4 kHz than for stimuli centered at 500 Hz. The data and their analysis, taken together, suggest that the findings reflect true across-frequency differences rather than being manifestations of response-related factors.
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43.66.Pn Binaural hearing
43.66.Ba Models and theories of auditory processes
43.66.Qp Localization of sound sources
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Noise tolerance in human frequency-following responses to voice pitch

Ximing Li and Fuh-Cherng Jeng

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. EL21-EL26 (2011); (6 pages)

Online Publication Date: 18 Jan 2011

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Speech communication usually occurs in the presence of background noise. This study examined noise tolerance in the brainstem’s processing of voice pitch, as reflected by the scalp-recorded frequency-following response (FFR) from 12 normal-hearing adults. By systematically manipulating signal-to-noise ratio (SNR) across three different stimulus intensities, the results indicated that Frequency Error, Slope Error, and Tracking Accuracy remained relatively stable until SNR was degraded to 0 dB or lower (i.e., a turning point). This turning point not only provided physiological evidence supporting pitch tolerance of noise but also allowed recommendation of a minimal SNR when evaluating pitch processing in difficult-to-test patients.
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43.64.Ri Evoked responses to sounds
43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Wn Effects of noise and trauma on the auditory system
43.64.Sj Neural responses to speech
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Investigations on the balloon as an impulse source

Jukka Pätynen, Brian F.G. Katz, and Tapio Lokki

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. EL27-EL33 (2011); (7 pages)

Online Publication Date: 18 Jan 2011

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Measurements of impulses produced by bursting balloons are presented. Various sizes of balloons were popped with a mechanical device in an anechoic chamber and recorded with a spherical microphone array. The power responses and directivity of the balloons are analyzed. Results indicate that power responses have two emphasized frequencies which depend on balloon size and inflation level. Larger balloons radiated more energy and higher inflation levels resulted in stronger high frequency content. Balloon directivity patterns are stable over repetitions. However, balloons do not radiate omnidirectionally. The degree of omnidirectionality improves with balloon size and for midrange frequencies.
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43.20.Ye Measurement methods and instrumentation
43.58.Gn Acoustic impulse analyzers and measurements
43.75.Zz Analysis, synthesis, and processing of musical sounds
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A method for evaluating the relation between sound source segregation and masking

Robert A. Lutfi and Ching-Ju Liu

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. EL34-EL38 (2011); (5 pages) | Cited 1 time

Online Publication Date: 18 Jan 2011

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Sound source segregation refers to the ability to hear as separate entities two or more sound sources comprising a mixture. Masking refers to the ability of one sound to make another sound difficult to hear. Often in studies, masking is assumed to result from a failure of segregation, but this assumption may not always be correct. Here a method is offered to identify the relation between masking and sound source segregation in studies and an example is given of its application.
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43.66.Ba Models and theories of auditory processes
43.66.Dc Masking
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Frequency discrimination duration effects for Huggins pitch and narrowband noise (L)

Christopher J. Plack, Martine Turgeon, Stuart Lancaster, Robert P. Carlyon, and Hedwig E. Gockel

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 1-4 (2011); (4 pages) | Cited 2 times

Online Publication Date: 02 Feb 2011

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Frequency difference limens (FDLs) were measured for Huggins pitch (HP) stimuli, consisting of a 30-Hz wide band of interaurally decorrelated noise in a diotic low-pass noise and for 30-Hz wide bands of diotic narrowband noise presented in a diotic low-pass noise background. FDLs at a 400-ms duration for the two stimulus types were equated by adjusting the level of the narrowband noise relative to the background. The effects of duration on the FDLs were then measured for center frequencies of 300, 600, and 900 Hz. Although the results were compromised by floor effects at 900 Hz, at 300 and 600 Hz, the duration effects were very similar for the HP and narrowband noise stimuli, with a large improvement in performance between 100 and 400 ms. In contrast to previous results for pure tones, the effect of duration was independent of frequency. The results suggest that: (1) Binaural and monaural pitches may be processed using a common mechanism; (2) discrimination performance for HP and low-sensation-level narrowband noise stimuli is not determined by the number of waveform periods.
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43.66.Hg Pitch
43.66.Fe Discrimination: intensity and frequency
43.66.Pn Binaural hearing
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
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Higher mode sound transmission from a point source through a rectangular aperture

J. L. Horner and K. S. Peat

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 5-11 (2011); (7 pages)

Online Publication Date: 02 Feb 2011

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This paper considers the higher-order scattered and transmitted wave fields that result when an acoustic wave from a point source impinges at an arbitrary angle on a rectangular aperture in a rigid, thick wall. In this analysis, it is assumed that free field conditions exist on both sides of the aperture. Although the full scattered and transmitted pressure fields contain both modal sum and modal coupling effects, the modal coupling effects of the higher-order modes are ignored such that an approximate analytical solution to the uncoupled analysis can be utilized. Experiments have been undertaken to measure the sound pressure levels in the transmitted field that result when sound from a point source impinges on the opposite side of a rectangular aperture. Measurements were made with the source located at the required position to drive a particular in-aperture higher-order mode. The source was also located at positions that did not directly excite any in-aperture higher-order mode at a cut-on frequency. These results indicate that the approximate analysis developed here gives accurate solutions whether or not any mode of the aperture is driven at cut-on. Thus, the method can be used for any relative location of a source from a rectangular aperture of any dimensions.
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43.20.Fn Scattering of acoustic waves

Acoustical scattering by multilayer spherical elastic scatterer containing electrorheological layer

Liang-Wu Cai, Dacio K. Dacol, Gregory J. Orris, David C. Calvo, and Michael Nicholas

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 12-23 (2011); (12 pages) | Cited 1 time

Online Publication Date: 02 Feb 2011

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A computational procedure for analyzing acoustical scattering by multilayer concentric spherical scatterers having an arbitrary mixture of acoustic and elastic materials is proposed. The procedure is then used to analyze the scattering by a spherical scatterer consisting of a solid shell and a solid core encasing an electrorheological (ER) fluid layer, and the tunability in the scattering characteristics afforded by the ER layer is explored numerically. Tunable scatterers with two different ER fluids are analyzed. One, corn starch in peanut oil, shows that a significant increase in scattering cross-section is possible in moderate frequencies. Another, fine poly-methyl methacrylate (PMMA) beads in dodecane, shows only slight change in scattering cross-sections overall. But, when the shell is thin, a noticeable local resonance peak can appear near ka = 1, and this resonance can be turned on or off by the external electric field.
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43.20.Fn Scattering of acoustic waves
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.35.Mr Acoustics of viscoelastic materials

Green’s function of radial inhomogeneous spheres excited by internal sources

Grigorios P. Zouros and Gerassimos C. Kokkorakis

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 24-31 (2011); (8 pages) | Cited 1 time

Online Publication Date: 02 Feb 2011

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Green’s function in the interior of penetrable bodies with inhomogeneous compressibility by sources placed inside them is evaluated through a Schwinger–Lippmann volume integral equation. In the case of a radial inhomogeneous sphere, the radial part of the unknown Green’s function can be expanded in a double Dini’s series, which allows analytical evaluation of the involved cumbersome integrals. The simple case treated here can be extended to more difficult situations involving inhomogeneous density as well as to the corresponding electromagnetic or elastic problem. Finally, numerical results are given for various inhomogeneous compressibility distributions.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.20.Ks Standing waves, resonance, normal modes
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Evaluation of a wave-vector-frequency-domain method for nonlinear wave propagation

Yun Jing, Molei Tao, and Greg T. Clement

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 32-46 (2011); (15 pages) | Cited 5 times

Online Publication Date: 02 Feb 2011

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A wave-vector-frequency-domain method is presented to describe one-directional forward or backward acoustic wave propagation in a nonlinear homogeneous medium. Starting from a frequency-domain representation of the second-order nonlinear acoustic wave equation, an implicit solution for the nonlinear term is proposed by employing the Green’s function. Its approximation, which is more suitable for numerical implementation, is used. An error study is carried out to test the efficiency of the model by comparing the results with the Fubini solution. It is shown that the error grows as the propagation distance and step-size increase. However, for the specific case tested, even at a step size as large as one wavelength, sufficient accuracy for plane-wave propagation is observed. A two-dimensional steered transducer problem is explored to verify the nonlinear acoustic field directional independence of the model. A three-dimensional single-element transducer problem is solved to verify the forward model by comparing it with an existing nonlinear wave propagation code. Finally, backward-projection behavior is examined. The sound field over a plane in an absorptive medium is backward projected to the source and compared with the initial field, where good agreement is observed.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
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Aspects of ground effect modeling

Gunnar Taraldsen and Hans Jonasson

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 47-53 (2011); (7 pages) | Cited 1 time

Online Publication Date: 02 Feb 2011

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A recently published one-parameter ground model based on Darcy’s law is here generalized into a two-parameter model which depends on an effective flow resistivity and an effective layer depth. Extensive field measurements of the acoustic impedance of various ground types have been carried out for frequencies in the range from 200 Hz to 2.5 kHz. The model based on Darcy’s law gives an improved fit to the measurements compared to the Delany–Bazley model. It is, in addition, argued on purely theoretical grounds that the suggested model is preferable. In contrast to the Delany–Bazley model it corresponds to a proper causal time-domain model. This is particularly relevant for extrapolation of the models to lower frequencies and for the recently developed harmonized methods intended for use in the implementation of the European Union directive on the assessment and management of environmental noise. The harmonized methods include frequencies down to the 25 Hz third octave band and have the Delany–Bazley ground impedance model as the default choice. The arguments presented here suggest that this default choice should be replaced by the more physically based model from the law of Darcy.
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43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.28.We Measurement methods and instrumentation for remote sensing and for inverse problems
43.28.Js Numerical models for outdoor propagation
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Interpretation of multi-frequency acoustic data: Effects of fish orientation

J. Michael Jech

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 54-63 (2011); (10 pages)

Online Publication Date: 02 Feb 2011

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One goal of fisheries acoustics is to develop objective classification or identification methods to automate allocation of acoustic backscatter to species. Classification schemes rely on consistent relationships for successful apportionment of acoustic backscatter to species. A method is developed that compares frequency-dependent volume backscatter from an acoustical survey of Atlantic herring (Clupea harengus) to investigate the potential for classifying herring. Predicted backscattering patterns by a Kirchhoff-ray approximation are used to explain the observed relationships and evaluate the potential for classification of multi-frequency data. Combining predicted backscatter with observations of the frequency-dependent volume backscatter gave approximately 40% classification success, which is not sufficient for survey purposes. However, this method highlighted potential consequences that fish orientation may have on classification schemes and density and abundance estimates. This method of comparing multi-frequency volume backscatter appears to be beneficial for detecting behavioral changes by groups of fish, which may be used to select target strength values for density or abundance estimates. Utilizing predicted target strengths from numerical or analytical solutions or approximations, appropriate target strengths could be selected and would provide more accurate estimates of fish density and abundance.
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43.30.Ft Volume scattering
43.30.Sf Acoustical detection of marine life; passive and active

Wind-generated ambient noise in a topographically isolated basin: A pre-industrial era proxy

D. Benjamin Reeder, Edmond S. Sheffield, and Susan M. Mach

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 64-73 (2011); (10 pages)

Online Publication Date: 02 Feb 2011

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During the mid-1980s, calibrated measurements of ambient noise and wind speed were made in the Tongue of the Ocean in the Bahamas to quantify the spectra and statistics of wind-generated noise. This deep basin is topographically isolated from the Atlantic Ocean and, therefore, largely acoustically decoupled from the Atlantic Ocean deep sound channel. The quantitative effects of contaminating (non-surface wind-generated) noise sources within the basin were eliminated by careful measurement and robust statistical analysis methodologies. Above 500 Hz, the spectral slopes are approximately −5 dB per octave and independent of wind speed. Below 500 Hz, the ambient noise is no longer a linear function of wind speed. Below 100 Hz and for wind speeds greater than 18.5 knots (kt), the ambient noise is independent of frequency. The minimum observed ambient noise level falls 13 dB below Urick’s “light shipping” level at 30 Hz and 2–5 dB below Wenz’s sea state zero level through the wind-dominated portion of the spectrum. The basin’s geographical isolation and the rigorous measurement and analysis methodologies employed make this two-decade-old data set a reasonable and justified proxy for pre-industrial era ocean noise levels in the 20 Hz to 20 kHz frequency band.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

The effect of coupling on bubble fragmentation acoustics

Helen Czerski and Grant B. Deane

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 74-84 (2011); (11 pages)

Online Publication Date: 02 Feb 2011

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Understanding the formation and evolution of bubble populations is important in a wide range of situations, including industrial processes, medical applications, and ocean science. Passive acoustical techniques can be used to track changes in the population, since each bubble formation or fragmentation event is likely to produce sound. This sound potentially contains a wealth of information about the fragmentation process and the products, but to fully exploit these data it is necessary to understand the physical processes that determine its characteristics. The focus of this paper is binary fragmentation, when turbulence causes one bubble to split into two. Specifically, the effect that bubble-bubble coupling has on the sound produced is examined. A numerical simulation of the acoustical excitation of fragmenting bubbles is used to generate model acoustic signals, which are compared with experimental data. A frequency range with a suppressed acoustic output which is observed in the experimental data can be explained when coupling is taken into account. In addition, although the driving mechanism of neck collapse is always consistent with the data for the larger bubble of the newly formed pair, a different mechanism must be driving the smaller bubble in some situations.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field

Target detection and localization in shallow water: An experimental demonstration of the acoustic barrier problem at the laboratory scale

Christian Marandet, Philippe Roux, Barbara Nicolas, and Jérôme Mars

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 85-97 (2011); (13 pages) | Cited 4 times

Online Publication Date: 02 Feb 2011

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This study demonstrates experimentally at the laboratory scale the detection and localization of a wavelength-sized target in a shallow ultrasonic waveguide between two source–receiver arrays at 3 MHz. In the framework of the acoustic barrier problem, at the 1/1000 scale, the waveguide represents a 1.1-km-long, 52-m-deep ocean acoustic channel in the kilohertz frequency range. The two coplanar arrays record in the time-domain the transfer matrix of the waveguide between each pair of source–receiver transducers. Invoking the reciprocity principle, a time-domain double-beamforming algorithm is simultaneously performed on the source and receiver arrays. This array processing projects the multireverberated acoustic echoes into an equivalent set of eigenrays, which are defined by their launch and arrival angles. Comparison is made between the intensity of each eigenray without and with a target for detection in the waveguide. Localization is performed through tomography inversion of the acoustic impedance of the target, using all of the eigenrays extracted from double beamforming. The use of the diffraction-based sensitivity kernel for each eigenray provides both the localization and the signature of the target. Experimental results are shown in the presence of surface waves, and methodological issues are discussed for detection and localization.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Fg Acoustic array systems and processing, beam-forming
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries

Fluctuating arrivals of short-range acoustic data

Cheolsoo Park, Woojae Seong, Peter Gerstoft, and William S. Hodgkiss

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 98-103 (2011); (6 pages)

Online Publication Date: 02 Feb 2011

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Geoacoustic inversion using fluctuating signal observations can be challenging. The origin of these fluctuations needs to be understood so the signals can be used appropriately. A set of experiments [Tang et al., Oceanogr. 20(4), 156–167 (2007)] was carried out in shallow water near the New Jersey shelf break in summer 2006. Significant fluctuations in the direct path and surface-reflected arrivals of short-range chirp transmissions (1.1–2.9 kHz) were observed on a vertical line array. This paper explains the origin of these signal fluctuations through analysis of the arrival amplitudes. It is shown that the strong thermocline combined with an oscillating source motion due to ocean surface waves results in the signal fluctuations.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Jn Source localization and parameter estimation
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Multiple scattering by cylinders immersed in fluid: High order approximations for the effective wavenumbers

Andrew N. Norris and Jean-Marc Conoir

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 104-113 (2011); (10 pages) | Cited 3 times

Online Publication Date: 02 Feb 2011

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Acoustic wave propagation in a fluid with a random assortment of identical cylindrical scatterers is considered. While the leading order correction to the effective wavenumber of the coherent wave is well established at dilute areal density (n0) of scatterers, in this paper the higher order dependence of the coherent wavenumber on n0 is developed in several directions. Starting from the quasi-crystalline approximation (QCA) a consistent method is described for continuing the Linton and Martin formula, which is second order in n0, to higher orders. Explicit formulas are provided for corrections to the effective wavenumber up to O (n04). Then, using the QCA theory as a basis, generalized self-consistent schemes are developed and compared with self-consistent schemes using other dynamic effective medium theories. It is shown that the Linton and Martin formula provides a closed self-consistent scheme, unlike other approaches.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.20.Fn Scattering of acoustic waves
43.20.Hq Velocity and attenuation of acoustic waves

Comparison between maximum radial expansion of ultrasound contrast agents and experimental postexcitation signal results

Daniel A. King and William D. O’Brien, Jr.

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 114-121 (2011); (8 pages) | Cited 2 times

Online Publication Date: 02 Feb 2011

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Experimental postexcitation signal data of collapsing Definity microbubbles are compared with the Marmottant theoretical model for large amplitude oscillations of ultrasound contrast agents (UCAs). After taking into account the insonifying pulse characteristics and size distribution of the population of UCAs, a good comparison between simulated results and previously measured experimental data is obtained by determining a threshold maximum radial expansion (Rmax) to indicate the onset of postexcitation. This threshold Rmax is found to range from 3.4 to 8.0 times the initial bubble radius, R0, depending on insonification frequency. These values are well above the typical free bubble inertial cavitation threshold commonly chosen at 2R0. The close agreement between the experiment and models suggests that lipid-shelled UCAs behave as unshelled bubbles during most of a large amplitude cavitation cycle, as proposed in the Marmottant equation.
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43.35.Ei Acoustic cavitation in liquids

Liquid compressibility effects during the collapse of a single cavitating bubble

D. Fuster, C. Dopazo, and G. Hauke

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 122-131 (2011); (10 pages)

Online Publication Date: 02 Feb 2011

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The effect of liquid compressibility on the dynamics of a single, spherical cavitating bubble is studied. While it is known that compressibility damps the amplitude of bubble rebounds, the extent to which this effect is accurately captured by weakly compressible versions of the Rayleigh–Plesset equation is unclear. To clarify this issue, partial differential equations governing conservation of mass, momentum, and energy are numerically solved both inside the bubble and in the surrounding compressible liquid. Radiated pressure waves originating at the unsteady bubble interface are directly captured. Results obtained with Rayleigh–Plesset type equations accounting for compressibility effects, proposed by Keller and Miksis [J. Acoust. Soc. Am. 68, 628–633 (1980)], Gilmore, and Tomita and Shima [Bull. JSME 20, 1453–1460 (1977)], are compared with those resulting from the full model. For strong collapses, the solution of the latter reveals that an important part of the energy concentrated during the collapse is used to generate an outgoing pressure wave. For the examples considered in this research, peak pressures are larger than those predicted by Rayleigh–Plesset type equations, whereas the amplitudes of the rebounds are smaller.
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43.35.Ei Acoustic cavitation in liquids
43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Hl Sonoluminescence
43.25.Gf Standing waves; resonance

Acoustical power amplification and damping by temperature gradients

Tetsushi Biwa, Ryo Komatsu, and Taichi Yazaki

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 132-137 (2011); (6 pages) | Cited 2 times

Online Publication Date: 02 Feb 2011

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Ceperley proposed a concept of a traveling wave heat engine [“A pistonless Stirling engine—The traveling wave heat engine,” J. Acoust. Soc. Am. 66, 1508–1513 (1979).] that provided a starting point of thermoacoustics today. This paper verifies experimentally his idea through observation of amplification and strong damping of a plane acoustic traveling wave as it passes through axial temperature gradients. The acoustic power gain is shown to obey a universal curve specified by a dimensionless parameter ωτα; ω is the angular frequency and τα is the relaxation time for the gas to thermally equilibrate with channel walls. As an application of his idea, a three-stage acoustic power amplifier is developed, which attains the gain up to 10 with a moderate temperature ratio of 2.3.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.38.Lc Amplifiers, attenuators, and audio controls
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Material selection for acoustic radiators that are light and stiff

S. P. Porter, D. C. Markley, D. J. Van Tol, and R. J. Meyer, Jr.

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 138-142 (2011); (5 pages)

Online Publication Date: 02 Feb 2011

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The headmass is a key element in tonpilz transducer design. As an acoustic radiator, a successful headmass must be built from a material that is both light and stiff. To assess the suitability of ceramics for this application, the authors used the mechanical properties of candidate materials to perform a theoretical comparison based on the flexural behavior of square plates. Although not a comprehensive metric for identifying the best headmass materials, the headmass flexure may be usefully employed as a first-level selection criteria. A software routine based on thin plate and thick plate theory was created to evaluate the flexural behavior in candidate materials.
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43.38.Ar Transducing principles, materials, and structures: general
43.40.Dx Vibrations of membranes and plates
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A synthesis approach for reproducing the response of aircraft panels to a turbulent boundary layer excitation

Teresa Bravo and Cédric Maury

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 143-153 (2011); (11 pages)

Online Publication Date: 02 Feb 2011

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Random wall-pressure fluctuations due to the turbulent boundary layer (TBL) are a feature of the air flow over an aircraft fuselage under cruise conditions, creating undesirable effects such as cabin noise annoyance. In order to test potential solutions to reduce the TBL-induced noise, a cost-efficient alternative to in-flight or wind-tunnel measurements involves the laboratory simulation of the response of aircraft sidewalls to high-speed subsonic TBL excitation. Previously published work has shown that TBL simulation using a near-field array of loudspeakers is only feasible in the low frequency range due to the rapid decay of the spanwise correlation length with frequency. This paper demonstrates through theoretical criteria how the wavenumber filtering capabilities of the radiating panel reduces the number of sources required, thus dramatically enlarging the frequency range over which the response of the TBL-excited panel is accurately reproduced. Experimental synthesis of the panel response to high-speed TBL excitation is found to be feasible over the hydrodynamic coincidence frequency range using a reduced set of near-field loudspeakers driven by optimal signals. Effective methodologies are proposed for an accurate reproduction of the TBL-induced sound power radiated by the panel into a free-field and when coupled to a cavity.
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43.40.Qi Effect of sound on structures, fatigue; spatial statistics of structural vibration
43.60.Fg Acoustic array systems and processing, beam-forming
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
43.28.Lv Statistical characteristics of sound fields and propagation parameters
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Experimental study of a smart foam sound absorber

Pierre Leroy, Alain Berry, Philippe Herzog, and Noureddine Atalla

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 154-164 (2011); (11 pages)

Online Publication Date: 02 Feb 2011

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This article presents the experimental implementation and results of a hybrid passive/active absorber (smart foam) made up from the combination of a passive absorbent (foam) and a curved polyvinylidene fluoride (PVDF) film actuator bonded to the rear surface of the foam. Various smart foam prototypes were built and tested in active absorption experiments conducted in an impedance tube under plane wave propagation condition at frequencies between 100 and 1500 Hz. Three control cases were tested. The first case used a fixed controller derived in the frequency domain from estimations of the primary disturbance at a directive microphone position in the tube and the transfer function between the control PVDF and the directive microphone. The two other cases used an adaptive time-domain feedforward controller to absorb either a single-frequency incident wave or a broadband incident wave. The non-linearity of the smart foams and the causality constraint were identified to be important factors influencing active control performance. The effectiveness of the various smart foam prototypes is discussed in terms of the active and passive absorption coefficients as well as the control voltage of the PVDF actuator normalized by the incident sound pressure.
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43.50.Ki Active noise control
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
43.38.Fx Piezoelectric and ferroelectric transducers

Mathematically trivial control of sound using a parametric beam focusing source

Nobuo Tanaka and Motoki Tanaka

J. Acoust. Soc. Am. Volume 129, Issue 1, pp. 165-172 (2011); (8 pages) | Cited 1 time

Online Publication Date: 02 Feb 2011

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Show Abstract
By exploiting a case regarded as trivial, this paper presents global active noise control using a parametric beam focusing source (PBFS). As with a dipole model, one is used for a primary sound source and the other for a control sound source, the control effect for minimizing a total acoustic power depends on the distance between the two. When the distance becomes zero, the total acoustic power becomes null, hence nothing less than a trivial case. Because of the constraints in practice, there exist difficulties in placing a control source close enough to a primary source. However, by projecting a sound beam of a parametric array loudspeaker onto the target sound source (primary source), a virtual sound source may be created on the target sound source, thereby enabling the collocation of the sources. In order to further ensure feasibility of the trivial case, a PBFS is then introduced in an effort to meet the size of the two sources. Reflected sound wave of the PBFS, which is tantamount to the virtual sound source output, aims to suppress the primary sound. Finally, a numerical analysis as well as an experiment is conducted, verifying the validity of the proposed methodology.
Show PACS
43.50.Ki Active noise control
43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.60.Fg Acoustic array systems and processing, beam-forming
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