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Mar 2012

Volume 131, Issue 3, pp. EL197-2555

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Analysis of acoustic parameters for consonant voicing classification in clean and telephone speech

Suk-Myung Lee and Jeung-Yoon Choi

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL197-EL202 (2012); (6 pages)

Online Publication Date: 08 Feb 2012

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This paper describes acoustic cues for classification of consonant voicing in a distinctive feature-based speech recognition system. Initial acoustic cues are selected by studying consonant production mechanisms. Spectral representations, band-limited energies, and correlation values, along with Mel-frequency cepstral coefficients features (MFCCs) are also examined. Analysis of variance is performed to assess relative significance of features. Overall, 82.2 %, 80.6 %, and 78.4 % classification rates are obtained on the TIMIT database for stops, fricatives, and affricates, respectively. Combining acoustic parameters with MFCCs shows performance improvement in all cases. Also, performance in the NTIMIT telephone channel speech shows that acoustic parameters are more robust than MFCCs.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.72.Kb Speech communication systems and dialogue systems
43.72.Ne Automatic speech recognition systems
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Aerial ultrasonic micro Doppler sonar detection range in outdoor environments

Marshall Bradley and James M. Sabatier

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL203-EL209 (2012); (7 pages)

Online Publication Date: 08 Feb 2012

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Current research demonstrates that micro Doppler sonar has the capability to uniquely identify the presence of a moving human, making it an attractive component in surveillance systems for border security applications. Primary environmental factors that limit sonar performance are two-way spreading losses, ultrasonic absorption, and backscattered energy from the ground that appears at zero Doppler shift in the sonar signal processor. Spectral leakage from the backscatter component has a significant effect on sonar performance for slow moving targets. Sonar performance is shown to rapidly decay as the sensor is moved closer to the ground due to increasing surface backscatter levels.
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43.80.Jz Use of acoustic energy (with or without other forms) in studies of structure and function of biological systems
43.20.Bi Mathematical theory of wave propagation
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Acoustically-observable properties of adult gait

Marshall Bradley and James M. Sabatier

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL210-EL215 (2012); (6 pages)

Online Publication Date: 08 Feb 2012

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An approach has been developed for extracting human gait parameters from micro Doppler sonar grams. Key parameters include average speed of walking, torso velocity, walk cycle time, and peak leg velocity. The approach is a modification of a technique previously used in radar data analysis. It has been adapted because of differences between sonar and radar micro Doppler grams. The approach has been applied to an acoustic data set of 16 female and 60 male walkers. Statistics have been tabulated that illustrate the similarities and dissimilarities between female and male gait. Males tend to walk with larger walk cycle times and peak leg velocities than females.
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43.80.Jz Use of acoustic energy (with or without other forms) in studies of structure and function of biological systems
43.20.Bi Mathematical theory of wave propagation
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Complement to standard method for measuring normal incidence sound transmission loss with three microphones

Yacoubou Salissou, Raymond Panneton, and Olivier Doutres

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL216-EL222 (2012); (7 pages)

Online Publication Date: 08 Feb 2012

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Complement to standard E2611-09 of the American Society for Testing and Materials [Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method (American Society for Testing and Materials, New York, 2009)] is proposed in order to measure normal incidence sound transmission loss of materials in a modified impedance tube using a three-microphone two-load or one-load method. The modified tube is a standard two-microphone impedance tube, where a third microphone is mounted on a movable hard termination. This method is conceptually identical to the four-microphone two-load or one-load method described in the standard; however, it requires fewer transfer functions and one microphone less. The method is validated on (1) symmetrical homogeneous and (2) non-symmetrical non-homogeneous specimens.
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43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.55.Rg Sound transmission through walls and through ducts: theory and measurement
43.58.Bh Acoustic impedance measurement
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Modulation cues influence binaural masking-level difference in masking-pattern experiments

Marc Nitschmann and Jesko L. Verhey

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL223-EL228 (2012); (6 pages)

Online Publication Date: 09 Feb 2012

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Binaural masking patterns show a steep decrease in the binaural masking-level difference (BMLD) when masker and signal have no frequency component in common. Experimental threshold data are presented together with model simulations for a diotic masker centered at 250 or 500 Hz and a bandwidth of 10 or 100 Hz masking a sinusoid interaurally in phase (S0) or in antiphase (Sπ). Simulations with a binaural model, including a modulation filterbank for the monaural analysis, indicate that a large portion of the decrease in the BMLD in remote-masking conditions may be due to an additional modulation cue available for monaural detection.
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43.66.Pn Binaural hearing
43.66.Dc Masking
43.66.Ba Models and theories of auditory processes
43.66.Rq Dichotic listening
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Some illustrative examples of the use of a spectral-element method in ocean acoustics

Paul Cristini and Dimitri Komatitsch

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL229-EL235 (2012); (7 pages)

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Some numerical results in the time domain obtained with the spectral-element method are presented in order to illustrate the high potential of this technique for modeling the propagation of acoustic waves in the ocean in complex configurations. A validation for a simple configuration with a known solution is shown, followed by some simulations of the propagation of acoustic waves over different types of ocean bottoms (fluid, elastic, and porous) to emphasize the wide variety of media that can be considered within the framework of this method. Finally, a movie illustrating upslope propagation over a viscoelastic wedge is presented and discussed.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.58.Ta Computers and computer programs in acoustics
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Rapid perceptual learning of noise-vocoded speech requires attention

Julia Jones Huyck and Ingrid S. Johnsrude

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL236-EL242 (2012); (7 pages)

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Humans are able to adapt to unfamiliar forms of speech (such as accented, time-compressed, or noise-vocoded speech) quite rapidly. Can such perceptual learning occur when attention is directed away from the speech signal? Here, participants were simultaneously exposed to noise-vocoded sentences, auditory distractors, and visual distractors. One group attended to the speech, listening to each sentence and reporting what they heard. Two other groups attended to either the auditory or visual distractors, performing a target-detection task. Only the attend-speech group benefited from the exposure when subsequently reporting noise-vocoded sentences. Thus, attention to noise-vocoded speech appears necessary for learning.
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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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Acoustical characterization of exploding hydrogen-oxygen balloons

Julia A. Vernon, Kent L. Gee, and Jeffrey H. Macedone

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL243-EL249 (2012); (7 pages)

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Exploding hydrogen-oxygen balloons are popular chemistry demonstrations. Although initial research experimentally quantified potential hearing risk via analysis of peak levels [K. L. Gee et al., J. Chem. Educ. 87, 1039–1044 (2010)], further waveform and spectral analyses have been conducted to more fully characterize these impulsive noise sources. While hydrogen-only balloons produce inconsistent reactions and relatively low, variable levels, stoichiometrically mixed hydrogen-oxygen balloons produce consistent high-amplitude noise waveforms. Preliminary consideration is also given to the potential use of these exploding balloons in architectural acoustics applications.
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43.50.Pn Impulse noise and noise due to impact
43.25.Vt Intense sound sources
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Probing of laser-induced crack modulation by laser-monitored surface waves and surface skimming bulk waves

Chen-Yin Ni, Nikolay Chigarev, Vincent Tournat, Nicolas Delorme, Zhong-Hua Shen, and Vitalyi E. Gusev

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL250-EL255 (2012); (6 pages)

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All-optical monitoring of the nonlinear motion of a surface-breaking crack is reported. Crack closing is induced by quasi-continuous laser heating, while Rayleigh surface acoustic pulses and bulk longitudinal surface skimming acoustic pulses are also generated and detected by lasers. By exploiting the strong dependence of the acoustic pulses reflection and transmission efficiency on the state—open or closed—of the contacts between the crack faces, the parametric modulation of ultrasonic pulses is achieved. It is observed that bulk acoustic waves skimming along the surface can be more sensitive to crack motion than Rayleigh surface waves.
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43.25.Fe Effect of nonlinearity on acoustic surface waves
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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A comparison of automatic and human speech recognition in null grammar

Amit Juneja

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL256-EL261 (2012); (6 pages)

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The accuracy of automatic speech recognition (ASR) systems is generally evaluated using corpora of grammatically sound read speech or natural spontaneous speech. This prohibits an accurate estimation of the performance of the acoustic modeling part of ASR because the language modeling performance is inherently integrated in the overall performance metric. In this work, ASR and human speech recognition (HSR) accuracies are compared for null grammar sentences in different signal-to-noise ratios and vocabulary sizes—1000, 2000, 4000, and 8000. The results shed light on differences between ASR and HSR in relative significance of bottom-up word recognition and context awareness.
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43.72.Ne Automatic speech recognition systems
43.72.Kb Speech communication systems and dialogue systems
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Model-based speech enhancement using a bone-conducted signal

Patrick Kechichian and Sriram Srinivasan

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL262-EL267 (2012); (6 pages)

Online Publication Date: 23 Feb 2012

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Codebook-based single-microphone noise suppressors, which exploit prior knowledge about speech and noise statistics, provide better performance in nonstationary noise. However, as the enhancement involves a joint optimization over speech and noise codebooks, this results in high computational complexity. A codebook-based method is proposed that uses a reference signal observed by a bone-conduction microphone, and a mapping between air- and bone-conduction codebook entries generated during an offline training phase. A smaller subset of air-conducted speech codebook entries that accurately models the clean speech signal is selected using this reference signal. Experiments support the expected improvement in performance at low computational complexity.
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43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.72.Kb Speech communication systems and dialogue systems
43.60.Vx Acoustic sensing and acquisition
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Auditory externalization in hearing-impaired listeners: The effect of pinna cues and number of talkers

Alan W. Boyd, William M. Whitmer, John J. Soraghan, and Michael A. Akeroyd

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL268-EL274 (2012); (7 pages)

Online Publication Date: 23 Feb 2012

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Hearing-aid wearers have reported sound source locations as being perceptually internalized (i.e., inside their head). The contribution of hearing-aid design to internalization has, however, received little attention. This experiment compared the sensitivity of hearing-impaired (HI) and normal-hearing listeners to externalization cues when listening with their own ears and simulated behind-the-ear hearing-aids in increasingly complex listening situations and reduced pinna cues. Participants rated the degree of externalization using a multiple-stimulus listening test for mixes of internalized and externalized speech stimuli presented over headphones. The results showed that HI listeners had a contracted perception of externalization correlated with high-frequency hearing loss.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Qp Localization of sound sources
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Analyzing the coda from correlating scattered surface waves

T. Dylan Mikesell, Kasper van Wijk, Thomas E. Blum, Roel Snieder, and Haruo Sato

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. EL275-EL281 (2012); (7 pages)

Online Publication Date: 24 Feb 2012

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The accuracy of scattered Rayleigh waves estimated using an interferometric method is investigated. Summing the cross correlations of the wave fields measured all around the scatterers yields the Green’s function between two excitation points. This accounts for the direct wave and the scattered field (coda). The correlations themselves provide insights into the location of the scatterers, as well as which scatterer is responsible for particular parts of the coda. Furthermore, these measurements confirm a constant-time arrival in the correlations, not part of the Green’s function, but which has previously been derived as a result of the generalized optical theorem.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.35.Pt Surface waves in solids and liquids
43.30.Zk Experimental modeling
43.20.Ye Measurement methods and instrumentation
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Pulse propagation in an elastic medium with quadratic nonlinearity (L)

Jianmin Qu, Peter B. Nagy, and Laurence J. Jacobs

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1827-1830 (2012); (4 pages)

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This letter examines the propagation of an acoustic pulse in an elastic medium with weak quadratic nonlinearity. Both a displacement pulse and a stress pulse of arbitrary shapes are used to generate the wave motion in the solid. By obtaining the explicit solutions for arbitrary pulse shapes, it is shown that for a sinusoidal tone-burst, in addition to a second order harmonic field, a radiation induced static strain field is also generated. These results help clarify some confusion in the recent literature regarding the shape of the propagating static displacement pulse.
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43.25.Dc Nonlinear acoustics of solids
43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Qp Radiation pressure
43.25.Ba Parameters of nonlinearity of the medium
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Green’s functions for a volume source in an elastic half-space

Evgenia A. Zabolotskaya, Yurii A. Ilinskii, Todd A. Hay, and Mark F. Hamilton

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1831-1842 (2012); (12 pages)

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Green’s functions are derived for elastic waves generated by a volume source in a homogeneous isotropic half-space. The context is sources at shallow burial depths, for which surface (Rayleigh) and bulk waves, both longitudinal and transverse, can be generated with comparable magnitudes. Two approaches are followed. First, the Green’s function is expanded with respect to eigenmodes that correspond to Rayleigh waves. While bulk waves are thus ignored, this approximation is valid on the surface far from the source, where the Rayleigh wave modes dominate. The second approach employs an angular spectrum that accounts for the bulk waves and yields a solution that may be separated into two terms. One is associated with bulk waves, the other with Rayleigh waves. The latter is proved to be identical to the Green’s function obtained following the first approach. The Green’s function obtained via angular spectrum decomposition is analyzed numerically in the time domain for different burial depths and distances to the receiver, and for parameters relevant to seismo-acoustic detection of land mines and other buried objects.
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43.20.Bi Mathematical theory of wave propagation
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves

Velocity and attenuation of scalar and elastic waves in random media: A spectral function approach

Marie Calvet and Ludovic Margerin

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1843-1862 (2012); (20 pages)

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This paper investigates the scattering of scalar and elastic waves in two-phase materials and single-mineral-cubic, hexagonal, orthorhombic-polycrystalline aggregates with randomly oriented grains. Based on the Dyson equation for the mean field, explicit expressions for the imaginary part of Green’s function in the frequency-wavenumber domain (ω, p), also known as the spectral function, are derived. This approach allows the identification of propagating modes with their relative contribution, and the computation of both attenuation and phase velocity for each mode. The results should be valid from the Rayleigh (low-frequency) to the geometrical optics (high-frequency) regime. Comparisons with other approaches are presented for both scalar and elastic waves.
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43.20.Bi Mathematical theory of wave propagation
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Jr Velocity and attenuation of elastic and poroelastic waves

Reflectance of acoustic horns and solution of the inverse problem

Daniel M. Rasetshwane, Stephen T. Neely, Jont B. Allen, and Christopher A. Shera

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1863-1873 (2012); (11 pages)

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A method is described for solving the inverse problem of determining the profile of an acoustic horn when time-domain reflectance (TDR) is known only at the entrance. The method involves recasting Webster’s horn equation in terms of forward and backward propagating wave variables. An essential feature of this method is a requirement that the backward propagating wave be continuous at the wave-front at all locations beyond the entrance. Derivation of the inverse solution raises questions about the meaning of causality in the context of wave propagation in non-uniform tubes. Exact reflectance expressions are presented for infinite exponential, conical and parabolic horns based on exact solutions of the horn equation. Diameter functions obtained with the inverse solution are a good match to all three horn profiles.
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43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Bi Mathematical theory of wave propagation

Propagation of guided waves through weak penetrable scatterers

Agnès Maurel and Jean-François Mercier

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1874-1889 (2012); (16 pages)

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The scattering of a scalar wave propagating in a waveguide containing weak penetrable scatterers is inspected in the Born approximation. The scatterers are of arbitrary shape and present a contrast both in density and in wavespeed (or bulk modulus), a situation that can be translated in the context of SH waves, water waves, or transverse electric/transverse magnetic polarized electromagnetic waves. For small size inclusions compared to the waveguide height, analytical expressions of the transmission and reflection coefficients are derived, and compared to results of direct numerical simulations. The cases of periodically and randomly distributed inclusions are considered in more detail, and compared with unbounded propagation through inclusions. Comparisons with previous results valid in the low frequency regime are proposed.
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43.20.Fn Scattering of acoustic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Bi Mathematical theory of wave propagation

On acoustic propagation in three-dimensional rectangular ducts with flexible walls and porous linings

Jane B. Lawrie

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1890-1901 (2012); (12 pages)

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The focus of this article is toward the development of hybrid analytic-numerical mode-matching methods for model problems involving three-dimensional ducts of rectangular cross-section and with flexible walls. Such methods require first closed form analytic expressions for the natural fluid-structure coupled waveforms that propagate in each duct section and second the corresponding orthogonality relations. It is demonstrated how recent theory [Lawrie, Proc. R. Soc. London, Ser. A 465, 2347–2367 (2009)] may be extended to a wide class of three-dimensional ducts, for example, those with a flexible wall and a porous lining (modeled as an equivalent fluid) or those with a flexible internal structure, such as a membrane (the “drum-like” silencer). Two equivalent expressions for the eigenmodes of a given duct can be formulated. For the ducts considered herein, the first ansatz is dependent on the eigenvalues/eigenfunctions appropriate for wave propagation in the corresponding two-dimensional flexible-walled duct, whereas the second takes the form of a Fourier series. The latter offers two advantages: no “root-finding” is involved and the method is appropriate for ducts in which the flexible wall is orthotropic. The first ansatz, however, provides important information about the orthogonality properties of the three-dimensional eigenmodes.
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43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Tb Interaction of vibrating structures with surrounding medium
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.

The effect of dissipation on the resistive admittance of an elastic medium

Douglas M. Photiadis

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1902-1909 (2012); (8 pages)

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The effect of dissipation on the real part of the admittance of an elastic half-space is typically thought to be unimportant if the loss factor ζ of the elastic medium is small. However, dissipation induces losses in the near field of the source and, provided the size of the source is small enough, this phenomenon can be more important than elastic wave radiation. Such losses give rise to a fundamental limit in the quality factor of an oscillator attached to a substrate. Near field losses associated with strains in the elastic substrate can actually be larger than intrinsic losses in the oscillator itself if the internal friction of the substrate is larger than the internal friction of the oscillator. For a uniform stress applied to a disk of radius a, a monopole source, such phenomena become significant for kLa<ζ, while for higher order multipole sources of order l, near field losses are important for (kLa)l+1<ζ, a far less restrictive constraint.
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43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.20.Tb Interaction of vibrating structures with surrounding medium
43.35.Mr Acoustics of viscoelastic materials
43.40.At Experimental and theoretical studies of vibrating systems

Eigenpairs of a coupled rectangular cavity and its fundamental properties

Nobuo Tanaka, Yusuke Takara, and Hiroyuki Iwamoto

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1910-1921 (2012); (12 pages)

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This paper deals with the eigenvalue problem of a coupled rectangular cavity comprising five rigid walls and one flexible panel frequently employed in much literature. It is the purpose of this paper to derive explicitly the eigenpairs of the coupled cavity, which are yet to be found. First, the coupling orthogonality conditions the eigenpairs need to satisfy are derived, thereby enabling the verification of the eigenpairs newly sought or already existent. Using the coupling orthogonality conditions, the modal equation of the coupled cavity system is then obtained, permitting one to deal with a forced response of the coupled cavity. It is shown that the eigenfunctions governing the dynamics of the sound field are expressed as the infinite sum of degenerate eigenfunctions. The characteristic matrix equation is then derived, specifying the eigenpairs of the coupled cavity. In order to investigate the fundamental properties of the eigenpairs derived, a numerical analysis is conducted, revealing the presence of evanescent modes in addition to the conventional standing wave modes. Finally, an experiment is carried out, verifying the validity of the eigenpairs derived in the article.
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43.20.Tb Interaction of vibrating structures with surrounding medium
43.20.Ks Standing waves, resonance, normal modes
43.40.Qi Effect of sound on structures, fatigue; spatial statistics of structural vibration
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Time reversed elastic nonlinearity diagnostic applied to mock osseointegration monitoring applying two experimental models

Jacques Rivière, Sylvain Haupert, Pascal Laugier, T. J. Ulrich, Pierre-Yves Le Bas, and Paul A. Johnson

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1922-1927 (2012); (6 pages)

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This study broadens vibration-like techniques developed for osseointegration monitoring to the nonlinear field. The time reversed elastic nonlinearity diagnostic is applied to two mock models. The first one consists of tightening a dental implant at different torques in a mock cortical bone; the second one allows one to follow glue curing at the interface between a dental implant and a mock jaw. Energy is focused near the implant interface using the time reversal technique. Two nonlinear procedures termed pulse inversion and the scaling subtraction method, already used successfully in other fields such as contrast agents and material characterization, are employed. These two procedures are compared for both models. The results suggest that nonlinear elasticity can provide new information regarding the interface, complementary to the linear wave velocity and attenuation. The curing experiment exhibits an overall low nonlinear level due to the fact that the glue significantly damps elastic nonlinearity at the interface. In contrast, the torque experiment shows strong nonlinearities at the focus time. Consequently, a parallel analysis of these models, both only partially reflecting a real case, enables one to envisage future in vivo experiments.
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43.25.Dc Nonlinear acoustics of solids

Reflection of compressional and Rayleigh waves on the edges of an elastic plate with quadratic nonlinearity

Thibaut B. Autrusson, Karim G. Sabra, and Michael J. Leamy

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1928-1937 (2012); (10 pages)

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Previous ultrasonic studies have demonstrated that measurements of material nonlinearities can provide a means for detecting early signs of fatigue damage using both compressional (P) and Rayleigh (R) surface waves. However, these experimental studies have typically been limited to the direct wave arrival between the source and receiver in simple geometries where no reflection occurs. In particular, the degree of material nonlinearity is often quantified by the ratio of the cumulative amplitude of the first harmonic to that of the fundamental for the direct arrival only. Hence a practical question arises over the interpretation of ultrasonic measurements of material nonlinearities in the presence of reflected nonlinear waves. Thus, this article investigates the reflection problem of P or R waves at the edge of a homogeneous plate with quadratic nonlinearity using both a theoretical formulation, based on perturbation analysis, and direct numerical simulations using a Cellular Automata formulation. The numerical approach is first validated against an existing theoretical formulation for reflecting nonlinear P waves. It is then used to simulate the nonlinear reflection of R waves at a plate’s edge for which no closed-form formulation is presently available.
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43.25.Dc Nonlinear acoustics of solids
43.25.Fe Effect of nonlinearity on acoustic surface waves
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

Product directivity models for parametric loudspeakers

Chuang Shi and Woon-Seng Gan

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1938-1945 (2012); (8 pages)

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In a recent work, the beamsteering characteristics of parametric loudspeakers were validated in an experiment. It was shown that based on the product directivity model, the locations and amplitudes of the mainlobe and grating lobes could be predicted within acceptable errors. However, the measured amplitudes of sidelobes have not been able to match the theoretical results accurately. In this paper, the original theories behind the product directivity model are revisited, and three modified product directivity models are proposed: (i) the advanced product directivity model, (ii) the exponential product directivity model, and (iii) the combined product directivity model. The proposed product directivity models take the radii of equivalent Gaussian sources into account and obtain better predictions of sidelobes for the difference frequency waves. From the comparison between measurement results and numerical solutions, all the proposed models outperform the original product directivity model in terms of selected sidelobe predictions by about 10 dB.
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43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.60.Fg Acoustic array systems and processing, beam-forming
43.38.Fx Piezoelectric and ferroelectric transducers
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A numerical approach to sound levels in near-surface refractive shadows

Sylvain Cheinet

J. Acoust. Soc. Am. Volume 131, Issue 3, pp. 1946-1958 (2012); (13 pages)

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The present study formulates a consistent method to simulate the outdoor, near-surface sound propagation through realistic refractive conditions. The correlated atmospheric stratification and turbulence properties are derived from standard meteorological quantities through flux-profile similarity relationships. The propagation of a monochromatic sound field is simulated in presence of the turbulence and stratification effects and an impedance ground. The propagation model uses a numerical solution of a second-order moment parabolic equation, which is introduced and evaluated. The so-formed coupled atmospheric-acoustic model is used to systematically investigate the sound levels in near-surface refractive shadows. In an illustrative propagation scenario, the shadow zone sound levels are predicted to show significant variations with the meteorological conditions. Specifically, the sound levels decrease with the adverse wind, as a consequence of enhanced mean upward refraction. Conversely, they increase with the absolute value of the surface heat flux, as a consequence of enhanced turbulence scattering. Implications for the assessment of the sound levels in shadow zones are discussed.
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43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.28.Js Numerical models for outdoor propagation
43.50.Vt Topographical and meteorological factors in noise propagation
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