bluuebunny/crossref_metadata_2025 huggingface dataset:
Gap detection and the precedence effect in young and old adults
Authors: Schneider Bruce A. , Pichora-Fuller Margaret Kathleen , Kowalchuk Danielle , Lamb Morag
Published: October 2005

Thresholds for detecting a gap between two Gaussian-enveloped (standard deviation=0.5 ms), 2-kHz tones were determined in young and old listeners. The gap-detection thresholds of old adults were more variable and about twice as large as those obtained from young adults. Moreover, gap-detection thresholds were not correlated with audiometric thresholds in either group. Estimates of the width of the temporal window of young subjects, based on the detection of a gap between two tone pips, were smaller than those typically obtained when a relatively long duration pure tone is interrupted [Moore et al., J. Acoust. Soc. Am. 85, 1266–1275 (1989)]. Because the amount of time it takes to recover from an adapting stimulus is likely to affect gap detection thresholds [Glasberg et al., J. Acoust. Soc. Am. 81, 1546–1556 (1987)], smaller estimates of temporal window size would be expected in this paradigm if the amount of adaptation produced by the first tone pip was negligible. The larger gap-detection thresholds of old subjects indicate that they may have larger temporal windows than young subjects. The lack of correlation between audiometric and gap-detection thresholds indicates that this loss of temporal acuity is not related to the degree of sensorineural hearing loss. In a second experiment on the precedence effect using the same subjects, a Gaussian-enveloped tone was presented over earphones to the left ear followed by the same tone pip presented to the right ear. To more realistically approximate a sound field situation, the tone pip presented to each ear was followed 0.6 ms later by an attenuated version presented to the contralateral ear. The delay between the left- and right-ear tone-pips was varied and the transition point between hearing a single tone on the left, and hearing two such sounds in close succession (one coming from the left and the other from the right) was determined. The transition point in this experiment did not differ between young and old subjects nor were these transition points correlated with gap-detection thresholds. These results indicate that monaural temporal acuity and binaural echo suppression may be based on different processes.
Effects on sound localization of configuration and type of hearing impairment
Authors: Noble William , Byrne Denis , Lepage Bernadette
Published: October 2005

Localization ability of 87 bilaterally hearing-impaired listeners was tested in the horizontal and vertical planes, frontally and laterally. In those with sensorineural hearing loss, it was found that deficits in localization accuracy in different regions of auditory space could be related to different configurations of hearing loss. For example, there were associations between vertical plane discrimination and high-frequency sensitivity; and front–rear discrimination and mid-to-high-frequency sensitivity. These results agree with theoretical expectations, while the outcome overall contrasts with previous reports that localization performance is unrelated to audiometric configuration. A comparison of 13 listeners with conductive/mixed types of impairment with a sensorineural-loss group, matched for degree of loss, showed that a conductive component adds significantly to localization disturbance, particularly in the horizontal plane. The probable reason is a disturbance of low-frequency interaural time cues, and this occurs because a higher proportion of low-frequency sound is likely to be transmitted via bone conduction relative to air conduction. Correlations between hearing loss and localization are only moderate, suggesting that aspects of hearing impairment, in addition to simple attenuation, may also reduce auditory localization performance.
Elastodynamic wave propagation in a continuously twisted structurally chiral medium along the axis of spirality
Authors: Lakhtakia Akhlesh
Published: October 2005

The stress tensor in a continuously twisted structurally chiral medium (CTSCM) is symmetric and the stiffness tensor varies helicoidally about the axis of spirality. Exact analytic solutions are found for elastodynamic wave propagation along the axis of spirality in a CTSCM.
Acoustic transient radiation from fluid-loaded shells of revolution using time-dependent in vacuo eigenvector expansions
Authors: Chen Huo-Wang , Stepanishen Peter
Published: October 2005

A new method is presented to evaluate the acoustic transient radiation from fluid-loaded shells of revolution which are excited by axisymmetric mechanical or acoustical excitations. This method is based on the use of an in-vacuo modal vector (eigenvector) expansion with time-dependent coefficients to describe the velocity field of the fluid-loaded shell. Modal acoustic impulse responses which account for the coupling between the in-vacuo modal vectors for the fluid-loaded shell are introduced in the formulation of the general solution. The time-dependent modal velocity coefficients are expressed as the solution of a set of coupled convolution integral equations which are readily solved by marching forward in time. The associated time-dependent surface pressure is subsequently expressed as a modal vector expansion in which the time-dependent coefficients are readily related to the modal velocity coefficients. Since the surface velocity and pressure are then known, the time-dependent pressures in the field are simply obtained via quadrature methods from the space-time Kirchhoff integral solution. The special case of a fluid-loaded spherical shell is addressed to illustrate the application of the method to determine the general characteristics of the transient velocity response of the shell and the associated pressure field resulting from axisymmetric mechanical force excitations of spherical shells. Numerical results are presented to illustrate the effects on the velocity response and pressure field of time-dependent fluid coupling between the modal vectors corresponding to the upper and lower branches of the in-vacuo frequency spectrum of the spherical shell.
Study of phase velocity and energy distribution of Stoneley waves at a solid–liquid interface
Authors: Guzhev Sergei N.
Published: October 2005

Characteristics of surface Stoneley (Scholte) waves propagating along the interface bismuth germanate–water solution of glycerol are investigated both theoretically and experimentally. These waves have been generated and detected using interdigital transducers (IDT). The phase velocity of the Stoneley wave and its energy distribution between the two media are measured at frequencies between 15 and 50 MHz over a wide region of sound speeds in the liquid vL, including those exceeding the speed of the Rayleigh wave in the solid vR. It is shown that at vL≳vR the speed of the Stoneley wave markedly differs (≳10%) from the speed of the longitudinal wave in the liquid. The former remains limited by vR, and the major part of wave energy propagates in the solid. The insertion and transducer losses (TL) were measured for the generation of Stoneley waves by the IDT; the minimal value of TL was close to 10 dB per transducer. This suggests that it is feasible to use this method for the generation of Stoneley waves.
Diffraction of acoustic waves by rigid plane baffles
Authors: Huang Ching-Jer , Chwang Allen T.
Published: October 2005

The integral-equation method is applied to study the diffraction of acoustic waves by rigid plane baffles, such as a circular disk and a ring. A set of six real Fredholm integral equations of the second kind is solved simultaneously to determine the velocity potentials on a circular disk. These equations are transformed into discrete forms by applying the Gauss–Legendre quadrature formula in the radial direction and the best possible numerical integration formula in the angular direction. The discrete equations are solved by the method of successive approximations, which is also called the direct integral-equation method. A new method is also developed to take care of integrations involving the Cauchy principal values, which occur when the moving point coincides with the fixed point. The accuracy of the present numerical approach has been tested by computing the excess-pressure ratio ‖p/p0‖ on the surfaces of a circular disk exposed to a plane wave and by comparing it with both analytical and experimental results. Our numerical results coincide with both results quite well, especially on the shadow side, where the diffraction field is not sensitive to the thickness of the circular disk. The effect of different parameters on the diffracted acoustic field about a circular disk due to a monochromatic acoustic source is systematically studied and compared. These parameters include the location of the acoustic source, the wave number, and the disk thickness. Some interesting results are obtained. As the wave number increases, the excess-pressure ratio approaches two on the ‘‘illuminated’’ side and zero on the ‘‘shadow’’ side of the disk, which indicates that Kirchhoff’s approximation is appropriate at higher wave numbers. As the acoustic source moves away from the symmetric axis toward one side, the bright spot on the shadow side moves toward the opposite side and has the same peak value. Finally, following the same approach as that for a circular disk, the diffraction of acoustic waves by a rigid ring is studied. Instead of six, a set of eight real Fredholm integral equations is solved simultaneously. The effect of different parameters on the diffraction field is also systematically studied and compared.
Coherent field and specular reflection at grazing incidence on a rough surface
Authors: Spivack Mark
Published: October 2005

The coherent component of the field scattered at grazing angles from a slightly rough pressure release surface is found. This is valid for multiple scattering and is based upon the parabolic integral equation method. Also examined are the scattering of planes waves under the method and in particular, the effect of truncating the boundary integral. It is shown that the coherent field remains invariant when the source and receiver are displaced vertically by equal and opposite distances, as was found numerically in a previous paper. In general, this can be shown to hold because the coherent field due to any plane wave is specular; however, under the parabolic equation method reflection is not specular, and thus the result is of particular interest. Reflection coefficients are given in closed form for several surface statistics, valid asymptotically at large distances.
New fast field programs for anisotropic sound propagation through an atmosphere with a wind velocity profile
Authors: Li Y. L. , White Michael J. , Franke S. J.
Published: October 2005

Two new fast field programs (FFP) have been developed for numerical computation of anisotropic sound propagation through an atmosphere with a wind velocity profile. The first new FFP can be used to compute the near-field and far-field sound pressure. The numerical implementation of the FFP is based on an integration algorithm using a two-dimensional fast Fourier transform with iterative refinement. For studying problems of long-range propagation, a novel far-field expression for sound pressure is derived. The second new FFP is based on this far-field approximation. If the magnitude of wind speed is not very large; this new far-field expression shows that the component of wind perpendicular to the direction of propagation has no effect on long-range propagation. Numerical results from both new fast field programs demonstrate that the effective sound-speed model used in the conventional FFP’s is still valid for propagation within a certain range. However, the agreement between methods becomes worse at longer horizontal distance. These numerical results also show that the effective sound-speed model will produce phase errors for higher angle modes, which is most apparent when a single mode dominates the solution. When many modes are present, the envelopes of the curves match, but the details do not.
Acoustics of the glass harmonica
Authors: Rossing Thomas D.
Published: October 2005

Glass harmonicas or glass harps, consisting of sets of tuned glasses, were already popular in Europe when Benjamin Franklin designed an improved style of instrument that he called an armonica. The modes of a wineglass resemble the flexural modes of a bell. Striking the glass excites a number of these modes, but rubbing the rim with a finger or bowing it radially with a violin bow generally excites a single mode. As the player’s finger moves around the rim of the glass, the nodes and antinodes move with it, resulting in a pulsating sound.
Jet formation and jet velocity fluctuations in a flue organ pipe
Authors: Verge M. P. , Fabre B. , Mahu W. E. A. , Hirschberg A. , van Hassel R. R. , Wijnands A. P. J. , de Vries J. J. , Hogendoorn C. J.
Published: October 2005

Flow visualization of the initial transient in a small recorderlike flue organ pipe is presented and the various stages of the jet formation are related to measurements of the acoustic response of the pipe. An initial acoustic signal, due to the unsteady volume flow of the jet, appears before the forming jet reaches the labium. This signal can easily be modeled using a low-frequency approximation. The initial trajectory of the jet makes a curve towards the exterior of the pipe. Under certain conditions, the jet may even, at first, miss the labium. This effect is related to the steepness of the pressure rise in the foot of the pipe. The initial impact of the jet with the labium appears to be a crucial factor in the triggering of the transient. Moving the labium towards the exterior of the pipe, using a steep pressure rise or putting ears around the mouth increase the chance that the jet will hit the labium. This initial impact is followed by an impulsive vortex shedding at the labium and subsequently a high-frequency varicoselike oscillation is observed on the jet. This oscillation is also observed without labium. After about three periods of the fundamental mode of the pipe, turbulence appears therefore destroying these coherent structures. Whereas the time dependency of the jet velocity dominates the first stage of the starting transient, the jet velocity fluctuations during steady-state result in a non-negligible damping. This loss mechanism is, for the fundamental mode of our experimental organ pipe, of the same order of magnitude as the radiation or visco-thermal damping.
Acoustics of the tenor high voice
Authors: Titze Ingo R. , Mapes Sharyn , Story Brad
Published: October 2005

The spectra of six tenors were analyzed at high pitches, F4 to B4. Because of the wide separation between harmonics, formant frequencies could not be extracted in the traditional way. Rather, an analysis-by-synthesis technique was used to match the spectra of a model to the measured spectra, using parameter optimization. Results suggest that tenors maintain their first formant frequencies well above the fundamental for all vowels except [u]. The purpose of this seems to be to distribute the acoustic energy between harmonics 2, 3, and 4 rather than to boost the fundamental. Tuning the first formant to the fundamental is a technique used effectively by sopranos but seems to be deliberately avoided by tenors in order to preserve a male quality.
Effect of temporal envelope smearing on speech reception
Authors: Drullman Rob , Festen Joost M. , Plomp Reinier
Published: October 2005

The effect of smearing the temporal envelope on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification was investigated for normal-hearing listeners. For this purpose, the speech signal was split up into a series of frequency bands (width of 1/4, 1/2, or 1 oct) and the amplitude envelope for each band was low-pass filtered at cutoff frequencies of 0, 1/2, 1, 2, 4, 8, 16, 32, or 64 Hz. Results for 36 subjects show (1) a severe reduction in sentence intelligibility for narrow processing bands at low cutoff frequencies (0–2 Hz); and (2) a marginal contribution of modulation frequencies above 16 Hz to the intelligibility of sentences (provided that lower modulation frequencies are completely present). For cutoff frequencies above 4 Hz, the SRT appears to be independent of the frequency bandwidth upon which envelope filtering takes place. Vowel and consonant identification with nonsense syllables were studied for cutoff frequencies of 0, 2, 4, 8, or 16 Hz in 1/4-oct bands. Results for 24 subjects indicate that consonants are more affected than vowels. Errors in vowel identification mainly consist of reduced recognition of diphthongs and of confusions between long and short vowels. In case of consonant recognition, stops appear to suffer most, with confusion patterns depending on the position in the syllable (initial, medial, or final).
Development of the Hearing In Noise Test for the measurement of speech reception thresholds in quiet and in noise
Authors: Nilsson Michael , Soli Sigfrid D. , Sullivan Jean A.
Published: October 2005

A large set of sentence materials, chosen for their uniformity in length and representation of natural speech, has been developed for the measurement of sentence speech reception thresholds (sSRTs). The mean-squared level of each digitally recorded sentence was adjusted to equate intelligibility when presented in spectrally matched noise to normal-hearing listeners. These materials were cast into 25 phonemically balanced lists of ten sentences for adaptive measurement of sentence sSRTs. The 95% confidence interval for these measurements is ±2.98 dB for sSRTs in quiet and ±2.41 dB for sSRTs in noise, as defined by the variability of repeated measures with different lists. Average sSRTs in quiet were 23.91 dB(A). Average sSRTs in 72 dB(A) noise were 69.08 dB(A), or −2.92 dB signal/noise ratio. Low-pass filtering increased sSRTs slightly in quiet and noise as the 4- and 8-kHz octave bands were eliminated. Much larger increases in SRT occurred when the 2-kHz octave band was eliminated, and bandwidth dropped below 2.5 kHz. Reliability was not degraded substantially until bandwidth dropped below 2.5 kHz. The statistical reliability and efficiency of the test suit it to practical applications in which measures of speech intelligibility are required.
Simulation study of changes in ultrasound speckle statistics with the system point spread function
Authors: Rao Navalgund A. H. K. , Zhu Hui
Published: October 2005

The intensity point signal-to-noise ratio, SNRI, characterizing the ultrasound speckle statistics, depends on the tissue scattering microstructure and the imaging systems point spread function. Both should be described in three-dimensional space. Therefore, a three-dimensional simulation model is used in this paper to generate a rf signal and study the variations in SNRI with the transducer center frequency and bandwidth. Results are in agreement with existing theoretical predictions. A possible method to analyze the SNRI data is also presented that can produce a straight line slope as a feature value that depends on the tissue scattering microstructure only. Such a feature may prove to be more useful than SNRI values in tissue characterization problems.
Listeners’ expectations about echoes can raise or lower echo threshold
Authors: Clifton Rachel K. , Freyman Richard L. , Litovsky Ruth Y. , McCall Daniel
Published: October 2005

Echo threshold increases with exposure to redundant trains of stimuli. Three experiments were conducted to test the hypothesis that a change in the ongoing train would affect listeners’ perception of the echo, but only if it signified an unusual change in room acoustics. The stimulus train was composed of 4-ms narrow-band noise bursts, with the leading sound from a loudspeaker placed 45° left of midline and the lagging sound or simulated echo from 45° right, delivered in an anechoic chamber.

The lagging sound in the test noise, which followed the train after a 750-ms pause, came randomly from loudspeakers at 35° or 55° right, and the listener’s task was to choose which position the echo came from on each trial. In experiment 1 the delay between onsets of the leading and lagging bursts was varied between train and test bursts, which simulated a sudden movement of the reflecting surface either toward the listener (if the delay of the test burst was shorter than the train) or away (if the delay was longer). In both cases listeners detected the echo’s direction more easily, compared to trials when there was no change between train and test burst delays. In order to check whether any change between train and test bursts would increase echo discriminability, experiment 2 varied frequency and experiment 3 varied intensity. These variations were not expected to affect the echo’s detectability because such changes signify that the original sound changed in these characteristics and the echo reflected these changes. These events are highly probable in the listener’s everyday experience because sound sources (and their reflections) typically vary in frequency and intensity content from moment to moment. As predicted, echo detectability in experiments 2 and 3 was not affected by whether the test noise bursts’ frequency or intensity was the same as the train’s or was varied. The results from all three experiments were interpreted in terms of listeners’ expectations about echoes.

It is proposed that echoes provide information about room acoustics, which the listener picks up during the ongoing sound and uses to form expectations about what will be heard. When expectations are violated by changes in the echo, this disruption can be seen in a lowering of echo threshold, relative to the ‘‘built-up’’ threshold when expectations are fulfilled.
Do infants perceive word boundaries? An empirical study of the bootstrapping of lexical acquisition
Authors: Christophe Anne , Dupoux Emmanuel , Bertoncini Josiane , Mehler Jacques
Published: October 2005

Babies, like adults, hear mostly continuous speech. Unlike adults, however, they are not acquainted with the words that constitute the utterances; yet in order to construct representations for words, they have to retrieve them from the speech wave. Given the apparent lack of obvious cues to word boundaries (such as pauses between words), this is not a trivial problem. Among the several mechanisms that could be explored to solve this bootstrapping problem for lexical acquisition, a tentative but reasonable one posits the existence of some cues (other than silence) that signal word boundaries. In order to test this hypothesis, infants were used as informants in our experiments. It was hypothesized that if word boundary cues exist, and if infants are to use them in the course of language acquisition, then they should at least perceive these cues. As a consequence, infants should be able to discriminate sequences that contain a word boundary from those that do not. A number of bisyllabic stimuli were extracted either from within French words (e.g., mati in mathématicien), or from between words (e.g., mati in panorama typique). Three-day-old infants were tested with a non-nutritive sucking paradigm, and the results of two experiments suggest that infants can discriminate between items that contain a word boundary and items that do not. It is therefore conceivable that newborns are already sensitive to cues that correlate with word boundaries. This result lends plausibility to the hypothesis that infants might use word boundary cues during lexical acquisition.
A corpus-based study of repair cues in spontaneous speech
Authors: Nakatani Christine H. , Hirschberg Julia
Published: October 2005

The occurrence of disfluencies in fully natural speech poses difficult challenges for spoken language understanding systems. For example, although self-repairs occur in about 10% of spontaneous utterances, they are often unmodeled in speech recognition systems. This is partly due to the fact that little is known about the extent to which cues in the speech signal may facilitate automatic repair processing. In this paper, acoustic and prosodic cues to self-repairs are identified, based on an analysis of a corpus taken from the ARPA Air Travel Information System database, and methods are proposed for exploiting these cues for repair detection, especially the task of modeling word fragments, and repair correction. The relative contributions of these speech-based cues, as well as other text-based repair cues, are examined in a statistical model of repair site detection that achieves a precision rate of 91% and recall of 86% on a prosodically labeled corpus of repair utterances.
The pitch of short-duration vibrato tones
Authors: d’Alessandro Christophe , Castellengo Michèle
Published: October 2005

The pitch perceived for short vocal vibrato tones was measured using a method of adjustment. The stimuli were synthetic vocal tones, produced by a formant synthesizer. The main parameter under study was the tone duration, as a function of the fractional number of vibrato cycles. This parameter was examined in relation to (1) the vibrato extent (0, 50, 100, and 200 cents); (2) the vibrato rate (4, 6, and 8 Hz); (3) the tone nominal frequency (220, 440, 880, and 1500 Hz). Durations ranging from 1/2 cycle to 2 cycles were studied. Our results showed that for short tones, the pitch perceived does correspond to a weighted time average of the F0 pattern. A separate perception took place for the high and low parts of the vibrato cycles, for large vibrato extents or slow vibrato rates. This phenomenon was related consistently with the glissando threshold. A simple numerical model of weighted time averaging with threshold was proposed. It demonstrated a good agreement with our experimental data. Finally, the experimental results obtained, and the model proposed, were able to explain the musical perception of complex F0 patterns, like those present in actual singing.
The effect of various physical parameters on the size and shape of necrosed tissue volume during ultrasound surgery
Authors: Damianou C. , Hynynen K.
Published: October 2005

The purpose of this study was to test the concept of using calculated thermal dose as a predictor for the necrosed tissue volume. A parametric study was conducted where the sonication parameters (pulse duration, power), transducer parameters (frequency, F number) and tissue properties (perfusion rate, attenuation) were varied and their effect on the lesion size was investigated. In vivo experiments where a focused ultrasound beam was used to induce tissue necrosis in thigh muscle of dog and rabbit were also conducted to obtain the reliability of the predictions. The experimental and simulated lesion sizes compared well. From the parametric study the threshold intensity for 1- and 5-s sonications were found to be about 1000 and 400 W/cm2, respectively. It was found that the lesion size was practically perfusion independent for pulses 5 s or shorter. The lesion size increases with increased pulse duration, acoustical power, and F number, but decreases with increased frequency provided that the focal intensity is kept constant. It was found also that the deeper the focus is in the tissue, the smaller the frequency range that causes selective tissue necrosis in the focal zone.
Downslope modal energy conversion
Authors: Chiu Ching-Sang
Published: October 2005

The significance of energy transfer between acoustic normal modes as they propagate downslope in a refractive sound channel is investigated. Specifically, two criteria for effective conversion of sound energy from high to low modes are established. In addition, the results from three simulation case studies are presented. These results show that for a low-frequency (70-Hz) bottom-lying sound source, the conversion of energy to the lowest modes is significant when the source depth is shallow. However such conversion does not occur when the depth of a bottom-lying source is near the axis of the deep sound channel.
Theory of the acoustical properties of multilayer and superlattice structures using an optical approach
Authors: Martin B. G.
Published: October 2005

A theoretical study has been made on adapting 2×2 optical transfer matrices for use in investigating the acoustical properties of multilayer structures, including superlattices. First, the acoustical transfer matrix for a single layer is obtained by analogy to the optical transfer matrix. Subsequently, various multilayer systems are considered and the results compared with those in the literature. The wavelength-dependent effective moduli for isotropic symmetric multilayers are obtained for the first time. These moduli reduce to known results in the long wavelength limit. It is concluded that the use of the acoustical analog of optical transfer matrices greatly simplifies investigation of the acoustical properties of multilayer media, including superlattices. In addition, it would enable one to adapt to acoustics, in a straightforward way, much of the vast literature on the optics of thin films.
Residual noise shaping technique for active noise control systems
Authors: Kuo Sen M. , Tsai Jianming
Published: October 2005

An active noise control system attenuates the overall sound field. However, in some applications, it is desirable to change the spectral contents of the residual noise. In this Letter, a residual noise spectrum shaping technique based on the filtered-E least-mean-square algorithm has been developed. This technique can be applied to active noise control of one-dimensional ducts and three-dimensional enclosures, for both narrow-band and broadband noises. Computer simulations demonstrate that this method not only attenuates the noise level, but also effectively reshapes the spectrum of the residual noise.
Expressions for the area under the chi-square receiver operating characteristic
Authors: Hautus Michael J.
Published: October 2005

Many psychophysical models propose chi-square random variables for the sensory evidence. This is true for the energy-detection model when Gaussian noise processes are being discriminated. Parametric equations for the chi-square receiver operating characteristic (ROC) are presented and then the index Ac, equal to the area under the chi-square ROC, is determined. The index Ac is shown to follow the incomplete beta distribution with parameters a=b=ν/2 and x=1/(k+1), where k=σ2n/σ2sn and ν is the number of degrees of freedom of the noise process.
The pitch of electrically presented sinusoids
Authors: Dorman Michael F. , Smith Michael , Smith Luther , Parkin James L.
Published: October 2005

A patient who uses the Ineraid cochlear implant, and who has hearing thresholds less than 50 dB HL for frequencies under 500 Hz in his nonimplanted ear, was asked to match the pitch of low-frequency signals presented to his two ears. The patient produced pitch matches, for frequencies of 125, 200, and 300 Hz presented to his most apical electrode, that were slightly higher than the reference frequency. When signals of fixed frequency were presented to electrodes located in successively more basal cochlear locations, pitch increased in an orderly fashion—an average of 57 Hz (range =31–87 Hz) for each change in electrode location.
Dispersive wave propagation in a viscoelastic matrix reinforced by elastic fibers
Authors: Kim Jin-Yeon , Ih Jeong-Guon , Lee Byung-Ho
Published: October 2005

Dispersion and attenuation characteristics of elastic waves propagating in viscoelastic fiber-reinforced composites are studied. The present analysis is based on the multiple scattering formulation for randomly distributed scatterers in an absorbing medium. Frequency-dependent complex material properties of the matrix are estimated from the attenuation coefficients by using the causality relationship between their real and imaginary parts. Pair-correlation functions for finding the accurate average of the T matrix are obtained by Monte Carlo simulation to study the dense fiber system. Resultant effective phase speed and total attenuation of longitudinal and shear waves are presented along the frequency varying the fiber volume fraction. In these results, fluctuations in dispersion and rapid increase in attenuation curves can be observed due to the resonance of fibers. Additionally, the shifts in resonance frequency from the single scattering resonance to higher frequency can be noted as the fiber volume fraction increases. Because the scattering dispersion is not strong in the low-frequency region, the viscoelastic dispersion is dominant in that region. It is possible to determine the dominant range of viscoelastic or scattering dispersion mechanisms depending on the frequency. In conclusion, the effect of the matrix viscoelasticity is very important in multiple scattering formulation for solving practical problems.
Scattering by an obstacle in a plane-stratified poroelastic medium: Application to an obstacle in ocean sediments
Authors: Lim Raymond
Published: October 2005

A transition-matrix formulation of the field scattered by a bounded three-dimensional obstacle buried in a plane-stratified, saturated, poroelastic environment is described. The formulation yields an exact solution of the vector Biot equations, obeying all boundary conditions prescribed on the layer and obstacle boundaries. This is obtained by combining the recently derived free-field transition matrix for an obstacle in a porous medium [S. G. Kargl and R. Lim, J. Acoust. Soc. Am. 94, 1527–1550 (1993)] with a generalization of existing acoustic waveguide solutions. The present solution is numerically implemented for an aluminum sphere buried in an ocean sediment half-space and insonified by an acoustic source in an overlying water half-space. Attention is paid to assessing the contribution of shear waves and slow compressional waves to the predicted backscatter.
Flexural response matrix for ribbed panels
Authors: Maidanik G. , Dickey J.
Published: October 2005

The formalism of the response of a ribbed membranelike panel that carries a single propagation type is recalled. The equation of motion is cast in a scalar form. The formalism is then extended to a ribbed membranelike panel that simultaneously carries two propagation types. The equation of motion is cast in a matrix form of rank 2. The formalism of the flexural response of a ribbed plate also admits to a matrix form of rank 2 and is akin to the formalism of the panel that carries two propagation types. However, fundamental differences also exist between these two formalisms. These differences are discussed and examined.
Monostatic and bistatic ray acoustic scattering by submerged elastic spherical shells
Authors: Ho Jin-Meng
Published: October 2005

This paper applies uniform ray asymptotics to plane-wave far-field scattering by submerged thin elastic spherical shells based on an earlier study [J. M. Ho and L. B. Felsen, J. Acoust. Soc. Am. 88, 2389–2414 (1990)]. It also performs numerical implementation to clarify the ray synthesis accuracy and to examine the constituent waves and fields. Specifically, in addition to the frequency response, the scattering pattern is also evaluated which demonstrates the connection between bistatic (regular) and backscattering (axial focusing). It is found that the major contribution to the total scattered field is from specular reflection, a supersonic compressional wave, and their interaction effect when adjacent, plus a creeping wave field in the forward scattering range—much the same as with the cylindrical shell prototype [J. M. Ho, J. Acoust. Soc. Am. 94, 2936–2946 (1993)], save from the spherical focusing of the shell-guided waves here. These wave objects together reproduce the scattering signature, as generated by the exact normal-mode series solution, very accurately for ka≥5 or so.
Transient interaction between impedance discontinuities on elastic vibrators using a convolution integral equation approach
Authors: Pathak Ardhendu G. , Stepanishen Peter R.
Published: October 2005

A general formulation is presented to address the problem of transient interaction between arbitrarily placed discontinuities on elastic vibrators, vibrating in-vacuo or in fluid. The Green’s function of the problem is used to formulate the force and the velocity response at the discontinuities, which leads to a system of coupled integral equations. These equations can be solved numerically by marching forward in time. The formulation is then applied for the case of a fluid-loaded infinite plate with line impedance discontinuities. Numerical results are presented for the case of a plate with two simple line supports, excited by a Gaussian modulated cosine wave line force. The advantages of using the chirp z transform for such problems are discussed. The time series for the forces acting at the support locations are interpreted in terms of the reflection at the supports, the dispersion characteristics of the plate, and the fluid loading effects.
Void-fraction measurements and sound-speed fields in bubble plumes generated by breaking waves
Authors: Lamarre Eric , Melville W. K.
Published: October 2005

Recent field and laboratory experiments have confirmed that low-frequency sound (10 to 300 Hz) is generated under breaking waves. It has been proposed that collective oscillations of the bubble plume generated by breaking may be the mechanism responsible for the generation of this sound. Confirmation of this process requires independent measurement of the void fraction, and therefore sound speed, in the bubbly mixture. Detailed measurements are presented of the evolution of the void-fraction field in bubble plumes generated by large-scale three-dimensional (3-D) laboratory breaking waves. Various moments of the void-fraction field are calculated and compared with results from two-dimensional (2-D) laboratory breaking waves [Lamarre and Melville, Nature 351, 469–472 (1991)]. The kinematics of the bubble plume reveals that the initial horizontal velocity of the plume is approximately 0.7C, where C is the wave phase speed. The centroid of the bubble plume is found to deepen at a speed of approximately 0.2H/T, where H and T are the wave height at breaking and the wave period, respectively. The radial dependence of the void-fraction and sound-speed field is characterized in terms of simple functions of time. Finally, the void-fraction measurements described here, along with independent measurements of the pressure fluctuations under breaking waves [Loewen and Melville, J. Acoust. Soc. Am. 95, 1329–1343 (1994)], support the hypothesis that low-frequency sound is generated by the collective oscillations of the bubble plume.
Mass sensitivity of acoustic plate mode liquid sensors on ZX–LiNbO3
Authors: Bender F. , Dahint R. , Josse F. , Grunze M. , Schickfus M. v.
Published: October 2005

Acoustic plate mode (APM) devices have been used as detectors in liquid environments. One of the primary detection mechanisms in such devices is mass loading. In the present work, the potential of APMs as mass sensitive biosensors is evaluated using five APM devices on ZX–LiNbO3 with frequencies of operation ranging from 13 to 42 MHz. Mass sensitivity is measured as a function of frequency and is compared to data predicted by perturbation theory. Discussions are given relative to typical antigen binding capacities of derivatized crystal surfaces.
Similitude in thermoacoustics
Authors: Olson J. R. , Swift G. W.
Published: October 2005

Similitude is applied to thermoacoustics without using the acoustic approximation. The equations which are important to thermoacoustics (continuity, motion, and heat transfer) are rewritten in dimensionless form, verifying that the list of dimensionless variables obtained from similitude is complete. Similitude is demonstrated in a thermoacoustic engine using helium, neon, and argon as working fluids, even for large-pressure-amplitude nonlinear behavior which differs significantly from predictions of linear thermoacoustic theory. Measurements are also presented for nitrogen and a helium–argon mixture, in order to reveal the influence of the specific-heat ratio and Prandtl number. Implications of similitude for building scale models are discussed; dimensions, temperatures, or pressures can be scaled.
Spectroscopy of resonant torsional modes in cylindrical rods using electromagnetic-acoustic transduction
Authors: Johnson Ward , Auld B. A. , Alers G. A.
Published: October 2005

Two ultrasonic techniques employing electromagnetic-acoustic transduction are presented for performing measurements of the resonant torsional frequencies and Q of solid cylindrical metallic rods. One of these techniques uses long radio-frequency pulses to drive the sample into resonance and the other uses continuous-wave excitation. Measurements are performed on an aluminum alloy. Since the transduction involves no mechanical coupling, the background damping is low; the Q is 1.2×105 at 755 kHz with the sample simply supported on its side. The shear velocity is determined with an accuracy of better than 2 parts in 104 (limited by the uncertainty in the measurement of the sample radius).
Approximate solutions of the dispersion equation for fluid-loaded cylindrical shells
Authors: Guo Y. P.
Published: October 2005

The dispersion equation for fluid-loaded cylindrical shells is solved to derive approximate analytical solutions that give complex wave numbers for elastic waves on the shell. Examples are given for shear, compressional, and flexural waves, which are known to be the dominant components in acoustic radiation and scattering problems in a wide frequency range. The derived approximate solutions are compared with results of numerical solutions, which shows very good accuracy.
A comprehensive expression for P–P measurements in planar standing waves
Authors: Guy R. W.
Published: October 2005

The latest draft standards from IEC and ASTM concerning P–P intensity probe qualification tests specify a standing wave test that addresses concerns for channel phase difference errors under reactive conditions. Two such errors are recognized, channel phase bias and back vent influences. The following analysis determines an expression for probe response, including both errors, when the probe is employed within a planar standing wave. This will lead to a better understanding of the test circumstances and may lead to generally applicable correction terms.
A hybrid numerical and analytical solution for the Green’s function of a fluid-loaded elastic plate
Authors: Cuschieri J. M. , Feit D.
Published: October 2005

A fundamental problem in structural acoustics is the scattering or radiation of sound from a fluid-loaded plate with discontinuities. In calculating the response of the plate, as well as the radiated pressure field, the traditional approach has been to evaluate the transform representation of the response or radiated pressure solution using a contour integral. The contour integral evaluation of these representations is numerically inefficient when compared to an approach that utilizes an FFT algorithm to compute the inverse transform by a direct integration along the real wave-number axis. The latter approach however can run into problems because of the presence of singularities along the real wave-number axis. In previous work by other investigators, this problem has been overcome by artificially including structural damping in their formulations, which in some instances may obscure the true effects of the radiation damping. In the present work, a direct integration approach is used after first analytically extracting from the solution the pole-like contributions on or near the real axis, and thus removing the problem of the singularities. The results only represent the influence of the radiation damping. The Green’s functions obtained in this way for the fluid-loaded plate are compared to results obtained by the other techniques. The resulting Green’s functions can be used to solve for the radiation and scattering problems for inhomogeneous fluid-loaded plates.
Effects of spectral smearing on the intelligibility of sentences in the presence of interfering speech
Authors: Baer Thomas , Moore Brian C. J.
Published: October 2005

In a previous study [T. Baer and B. C. J. Moore, J. Acoust. Soc. Am. 94, 1229–1241 (1993)], a spectral smearing technique was used to simulate some of the effects of impaired frequency selectivity so as to assess its influence on speech intelligibility. Results showed that spectral smearing to simulate broadening of the auditory filters by a factor of 3 or 6 had little effect on the intelligibility of speech in quiet but had a large effect on the intelligibility of speech in noise. The present study examines the effect of spectral smearing on the intelligibility of speech in the presence of a single interfering talker. The results were generally consistent with those of the previous study, suggesting that impaired frequency selectivity contributes significantly to the problems experienced by people with cochlear hearing loss when they listen to speech in the presence of interfering sounds.
Wave description of near-field scattering from cylindrical shells
Authors: Guo Y. P.
Published: October 2005

Asymptotic analysis is used to study the near field of sound scattering from cylindrical shells, including both shell responses and near-field pressure fluctuations. Explicit analytical solutions are given in terms of excited waves on the shell. Though derived by making use of high-frequency asymptotics, these solutions are shown to have very high accuracy in both the mid- and high-frequency domain. By using the derived solutions, contributions to shell responses respectively from compressional and shear waves are examined to reveal energy partition between these waves and to assess their relative coupling efficiency to the acoustic field.
Evaluating the analytic solution to a three-dimensional boundary value problem in elasticity using Shanks’ transformation
Authors: Oakes Alexandria
Published: October 2005

This paper is the second of a three-part series in which solutions are given to two-dimensional and three-dimensional boundary value problems in elasticity. Using the convergence technique developed in the first part to evaluate the stress in the near zone of a semi-infinite slab subject to static loading, this same technique is now applied in two ways to evaluate the dynamic response of a three-dimensional solid cylinder subject to time-dependent end loading.
Model-based processor design for a shallow water ocean acoustic experiment
Authors: Candy J. V. , Sullivan E. J.
Published: October 2005

Model-based signal processing is a well-defined methodology enabling the inclusion of environmental (propagation) models, measurement (sensor arrays) models, and noise (shipping, measurement) models into a sophisticated processing algorithm. Depending on the class of model developed from the mathematical representation of the physical phenomenology, various processors can evolve. Here the design of a space-varying, nonstationary, model-based processor (MBP) is investigated and applied to the data from a well-controlled shallow water experiment performed at Hudson Canyon. This particular experiment is very attractive for the inaugural application of the MBP because it was performed in shallow water at low frequency requiring a small number of modes. In essence, the Hudson Canyon represents a well-known ocean environment, making it ideal for this investigation. In this shallow water application, a state-space representation of the normal-mode propagation model is used. The processor is designed such that it allows in situ recursive estimation of both the pressure-field and modal functions. It is shown that the MBP can be effectively utilized to ‘‘validate’’ the performance of the model on noisy ocean acoustic data. In fact, a set of processors is designed, one for each source range and the results are quite good—implying that the propagation model with measured parameters adequately represents the data.