bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic levitation in the presence of gravity
Authors: Collas P. , Barmatz M. , Shipley C.
Published: October 2005

The method of Gor’kov has been applied to derive general expressions for the total potential and force on a small spherical object in a resonant chamber in the presence of both acoustic and gravitational force fields. The levitation position is also determined in rectangular resonators for the simultaneous excitation of up to three acoustic modes, and the results are applied to the triple-axis acoustic levitator. The analysis is applied to rectangular, spherical, and cylindrical single-mode levitators that are arbitrarily oriented relative to the gravitational force field. Criteria are determined for isotropic force fields in rectangular and cylindrical resonators. It is demonstrated that an object will be situated within a volume of possible levitation positions at a point determined by the relative strength of the acoustic and gravitational fields and the orientation of the chamber relative to gravity. Trajectories of an object from an arbitrary starting position to a final equilibrium position are also discussed.
Assessment of a new radiation damping model for structural acoustic interactions
Authors: Kriegsmann Gregory A. , Scandrett Clyde L.
Published: October 2005

The equations that govern the scattering of acoustic waves from a baffled membrane strip couple the fluid pressure and the membrane displacement in an intimate way. The equations cannot be decoupled and consequently analytical solutions cannot be found. Approximate methods are often used to decouple the system. A new approximate method is presented, which can be classified as an ‘‘impedance approximation,’’ in that it relates the membrane displacement to a differential operator applied to the fluid pressure at the membrane surface. The differential operator arises from applying a radiation condition, which is strictly valid far away from the structure, to the pressure on the membrane’s surface. This new technique is compared to the plane-wave approximation method and to a finite difference solution of the fully coupled system. It is found that the new approximation method improves upon the plane-wave approximation method, particularly near the in vacuo eigenfrequencies of the membrane.
Analysis of a hybrid noise control system for a duct
Authors: Munjal M. L. , Eriksson L. J.
Published: October 2005

This letter proposes the combination of a passive muffler and an active noise control system for the control of very high-level noise in ducts used with large industrial fans and similar equipment. The analysis of such a hybrid system is presented making use of electroacoustic analogies and the transfer matrix method. It turns out that a passive muffler upstream of the input microphone can indeed lower the acoustic pressure and, hence, the power requirement of the auxiliary source. The parameter that needs to be optimized (or maximized) for this purpose is a certain velocity ratio that can readily be evaluated in a closed form, making it more or less straightforward to synthesize the configuration of an effective passive muffler to go with the active noise control system.
Frequency and time variations of the first formant: Properties relevant to the perception of vowel height
Authors: Di Benedetto Maria-Gabriella
Published: October 2005

Perceptual experiments using consonant–vowel–consonant (CVC) syllables were carried out to examine the perceptual relevance of the first formant frequency (F1) trajectory in the perception of high vowels versus nonhigh vowels. Results show that stimuli characterized by a higher onset frequency and F1 maximum at the beginning of the vocalic portion are perceived as lower vowels than stimuli with a lower F1 onset frequency and F1 maximum toward the end of the vocalic portion. These findings are in agreement with the hypothesis, based on the acoustic analyses of Di Benedetto (1989), that stimuli with higher F1 onset frequencies and F1 maximum at the beginning of the vocalic portion characterize lower vowels. Results are similar for native speakers of different languages, leading to a suggestion that this phenomenon may have either an articulatory or an auditory basis. Possible interpretations based on an overshoot hypothesis or a formant time average theory were investigated through an additional perceptual experiment. Results of this last experiment agree with a weighted average time formant theory.
Kinematic and electromyographic responses to perturbation of the jaw
Authors: Shaiman Susan
Published: October 2005

The task-dependent organization of sensorimotor mechanisms during the production of speech was investigated using a perturbation paradigm. Six subjects received unanticipated jaw perturbations before and during tongue elevation for [1d1], in which the lips do not participate, and bilabial closure for [1b1], in which the tongue does not participate. A strain gauge system was used to monitor inferior–superior displacements of the upper lip, lower lip, and jaw, while hooked-wire electrodes monitored muscle activity in various muscles of the lips, jaw, and tongue. Results indicated significant compensatory kinematic adjustments to jaw perturbations in the lips and/or jaw during [1b1], but no labial compensations during [1d1] (with the exception of one subject). EMG responses were inconsistent and not necessarily indicative of the kinematic findings. Individual subjects responded to perturbations reliably but differently, using different combinations of involved articulators to achieve bilabial closure and lingua–alveolar contact. The current study supports earlier research which suggests that the components of the motor system are flexibly assembled, based on the requirements of the specific task. That is, compensatory responses to sensory information occur only when such responses are functionally necessary.
Differences in echolocation click patterns of the beluga (D
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l
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n
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s l
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s) and the bottlenose dolphin (T
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s t
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s)
Authors: Turl Charles W. , Penner Ralph H.
Published: October 2005

In an echolocation experiment, the target detection performance of a beluga and a bottlenose dolphin were similar, but each produced different patterns of echolocation click trains. The beluga emitted three different patterns of echolocation clicks. A pattern I click train started with low-amplitude clicks, followed by packets of clicks. A packet contained several clicks with interclick intervals less than the two-way travel time to the target; the interpacket intervals were greater than the two-way travel time. A pattern II click train consisted of a combination of individual clicks, some with intervals less than and some greater than the two-way travel time. This pattern did not contain packets. The third pattern of click trains consisted of individual clicks with interclick intervals less than the two-way travel time. However, the bottlenose dolphin always emitted clicks with interclick intervals greater than the two-way travel time. These differences in click patterns suggest that the beluga has a different echolocation strategy than the bottlenose dolphin.
Use of vowel duration information in a large vocabulary word recognizer
Authors: Deng L. , Lennig M. , Mermelstein P.
Published: October 2005

In this paper, a method is developed to employ vowel duration properties in a hidden Markov model (HMM)-based large vocabulary speaker trained recognition system. It is found that each of the vowel phonemes spoken in isolated words can be divided into three allophones, each corresponding to a largely distinctive range of vowel durations. Such a division is based upon the phonetic context where the vowel occurs. In order to incorporate the durational information, each vowel’s HMM is trained using a maximum-likelihood method with three separate sets of transition probabilities, corresponding to the three allophones. The output distributions of the HMM are assumed to be the same for all three allophones and trained jointly, to make best use of the limited number of available training tokens. The duration-specific HMMs for vowel allophones have been evaluated in isolated word recognition experiments for two male speakers. The results show that the performance of the recognizer is improved, reducing the error rate by approximately 14% compared with recognition results without the use of the vowel durational models. The performance improvement resulting from use of the vowel durational models is due to reduction of postvocalic consonant errors arising from their contextual correlation with vowels of different durations, as well as to improved discrimination between vowel phonemes.
The effect of varying the amplitude-frequency response on the masked speech-reception threshold of sentences for hearing-impaired listeners
Authors: van Dijkhuizen Janette N. , Festen Joost M. , Plomp Reinier
Published: October 2005

In an evaluation of frequency-dependent automatic gain-control systems in hearing aids, the effect of varying the amplitude-frequency response on the speech-reception threshold (SRT) for sentences in noise is studied for 20 hearing-impaired listeners. The noise has a spectrum identical to the long-term average spectrum of the sentences. Speech and noise are shaped by the same amplitude-frequency response; their spectra are varied relative to the bisector of the individual’s dynamic range. In four experimental conditions, the effect of a steady-state amplitude-frequency response is studied. Steepening the negative spectral slope of speech and noise appears to cause an increase of masked SRT, possibly due to increased effect of upward spread of masking. The effect of a single transition of the amplitude-frequency response between 10 and −10 dB/oct halfway through the sentence seems to be related to the effect for the fixed −10-dB/oct condition. Two transition times are tested. For a transition time of 0.25 s, the SRT is only a little higher than for 1 s. The results suggest that the amplitude-frequency response may be varied in time without having a detrimental effect on the masked SRT of sentences for hearing-impaired listeners as long as strongly negatively sloping spectra are avoided.
Three-dimensional elastic wave scattering by surface-breaking cracks
Authors: Budreck D. E. , Achenbach J. D.
Published: October 2005

Scattering of time-harmonic elastic waves by a surface-breaking crack of arbitrary shape, which is normal to the traction-free surface of a half-space, is investigated by the boundary integral equation method. The use of full-space Green’s functions requires a discretization of the free surface near the crack mouth. Convergence of the crack-opening displacements with successively larger regions of discretization of the free surface is demonstrated. The crack-opening displacements are used to calculate the farfield amplitude spectra of scattered longitudinal and transverse body waves. The required representation integral makes use of the farfield expansions of the half-space Green’s functions. Solutions of both symmetric and antisymmetric problems are obtained by considering two special angles of incidence of a transverse wave field. Numerical results, in the form of crack-opening displacements and scattered farfield amplitude distributions, are presented for scattering by a semicircular normal-edge crack of radius a. A breakdown of contributions to the farfield amplitudes, by ray cases, provides insight as to the relative strengths of the signals radiating from the crack along the various ray paths.
Response to ‘‘Comments on ‘Spectrum factors relevant to phonetogram measurement’ ’’[J. Acoust. Soc. Am. 8
6, 423–424 (1989)]
Authors: Gramming Patricia , Sundberg Johan
Published: October 2005

In this letter, the authors reply to comments written by F. Klingholz [J. Acoust. Soc. Am. 86, XXX–XXX (1989)] on an earlier article by Gramming and Sundberg [J. Acoust. Soc. Am. 83, 2352–2360 (1988)].
Comments on ‘‘The negative effect of amplitude compression in multichannel hearing aids in the light of the modulation-transfer function’’ [J. Acoust. Soc. Am. 8
3, 2322–2327 (1988)]
Authors: Villchur Edgar
Published: October 2005

According to Plomp [J. Acoust. Soc. Am. 83, 2322–2327 (1988)], fast multichannel amplitude compression has a predictably negative effect on speech intelligibility for both normal and impaired listeners. The following letter is a response to that conclusion.
Reply to ‘‘Comments on ‘The negative effect of amplitude compression in multichannel hearing aids in the light of the modulation-transfer function’ ’’ [J. Acoust. Soc. Am. 8
6, 425–427 (1989)]
Authors: Plomp Reinier
Published: October 2005

A reply is given to ‘‘Comments on ‘The negative effect of amplitude compression in multichannel hearing aids in the light of the modulation-transfer function’ [J. Acoust. Soc. Am. 86, XXX–XXX (1989)].’’ Data rather than arguments are needed.
Quantization and measurement errors in the analysis of short-time perturbations in sampled data
Authors: Cox Neil B. , Ito Mabo R. , Morrison Murray D.
Published: October 2005

This paper provides an analysis of the effect of quantization and measurement errors on two algorithms for measuring short-time perturbation about a slowly varying or periodically varying mean. While these algorithms can be applied in a variety of applications, they will be discussed in the context of their use in quantification of vowel perturbations associated with hoarseness. The algorithms are referred to as the relative average perturbation and the directional perturbation quotient in speech analysis literature. The analyses indicate that significant errors are present in published studies. Sampling conditions and analysis techniques to minimize these errors are described.
Acoustic radiation from an insonified elastic plate with a line discontinuity
Authors: Seren Cetin , Hayek Sabih I.
Published: October 2005

This paper deals with the development of analytic models for the prediction of the acoustic radiated field from an infinite elastic plate with a single line force and line moment impedance discontinuity due to an incident plane acoustic wave. The solution is in the form of a Fourier integral with a kernel having ten poles. The integral is evaluated by three methods. The first uses the steepest descent path (SDP) method, leading to a solution that decays as 1/(k0r)1/2. The second method used conformal transformations and the modified saddle point (MSP) method, where all ten poles of the integrand are factored out. This second method yields a solution that has complementary error functions and an asymptotic series in (k0r). The third method employs a transformation of the integrand to effect an efficient and fastly convergent numerical integration algorithm. In general, the MSP asymptotic series solution and the numerical integration yielded numerically identical results. However, while the SDP solution predicted a similar directivity function, it predicted numerically higher values than the MSP solution by as much as 20 dB for observers located close to the discontinuity. The three solutions converged for higher values of k0r, the convergence being slower for higher frequencies, especially above the coincidence frequency.
Intensity discrimination determined with two paradigms in normal and hearing-impaired subjects
Authors: Turner Christopher W. , Zwislocki Jozef J. , Filion Paul R.
Published: October 2005

The literature on auditory intensity jnd’s is ambiguous with respect to the relationship between the jnd’s measured with gated and continuous pedestals and with respect to changes in this relationship in the presence of loudness recruitment accompanying cochlear pathology. In an attempt to clarify these issues and to lay a foundation for systematic investigations of the dependence on the jnd’s on loudness functions, the jnd’s for pure tones with gated- and continuous-pedestal paradigms of two groups of subjects, one with normal hearing and one with hearing loss of cochlear origin, were measured. The experiments were performed at 0.5, 2, and 6 kHz, and at a wide range of sensation levels (SLs) by means of an adaptive two-alternative, forced-choice (2IFC) procedure. The jnd’s obtained with the continuous-pedestal method were smaller than those obtained with the gated-pedestal method for both groups of subjects. They also had smaller intersubject standard deviations. When jnd’s of the two groups were compared on the basis of equal SLs, the group with hearing loss showed smaller jnd values than the group with normal hearing for both pedestal paradigms. When the comparisons were made on the basis of equal sound-pressure levels (SPLs), both groups showed similar values for moderate and high SPLs. At relatively low SPLs, the group with hearing loss tended to have somewhat higher values.
Perception of complex tone pairs mistuned from unison
Authors: Warren Richard M. , Bashford James A. , Brubaker Bradley S.
Published: October 2005

Periodic sounds mistuned from unison may interact to produce pitch glides: When a broad-spectrum complex tone having a fundamental frequency of 400 Hz or less and containing several harmonics above the 8th is mixed with itself after a slight change in the waveform repetition frequency (1 Hz or less), listeners hear a rising glissando when corresponding portions of the waveforms approach alignment and a falling glissando as they recede from alignment. Glissandi are unimpaired if harmonics below the 8th are absent, but if, instead, harmonics above the 8th are removed, only amplitude fluctuations are heard (not glissandi). When two broad-spectrum complex tones with independent, randomly derived phase spectra are mistuned slightly from unison and mixed, complex repeated patterns other than glissandi are heard. These observations, along with others involving a variety of periodic sounds mistuned from unison, provide information concerning the nature of frequency domain and time domain mechanisms employed for the perception of iterated acoustic patterns.
An efficient enhancement of finite-difference implementations for solving parabolic equations
Authors: Robertson J. S. , Arney D. C. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

The parabolic approximation method is widely recognized as useful for accurately analyzing and predicting sound transmission intensity in diverse ocean environments. One reason for its attractiveness is that solutions are marched in range, thereby avoiding the large internal storage requirements when using the full wave equation. Present finite-difference implementations employ a range step size that is prescribed by either the user or the code and that remains fixed for the duration of the computation. An algorithm is presented in which the range step is adaptively selected by a procedure within a version of the implicit finite-difference (IFD) implementation of the parabolic approximation. An error indicator is computed at each range step, and its value is compared to an error tolerance window that is readily specified by the user. If the error indicator falls outside this window, a new range step size is computed and used until the error indicator again leaves the tolerance window. Furthermore, for a given tolerance, this algorithm generates a range step size that is optimal in a specified sense and that often leads to large decreases in run time. Additional related modifications to the IFD implementations are discussed. Several examples are presented that illustrate the efficacy of the enhanced algorithm.
The validity of the perturbation approximation for rough surface scattering using a Gaussian roughness spectrum
Authors: Thorsos Eric I. , Jackson Darrell R.
Published: October 2005

The validity of the perturbation approximation for rough surface scattering is examined (1) by comparison with exact results obtained by solving an integral equation and (2) through comparison of low-order perturbation predictions with higher-order predictions. The pressure release boundary condition is assumed, and the field quantity calculated is the bistatic scattering cross section. A Gaussian roughness spectrum is used, and the surfaces have height variations in only one direction. It is found, in general, that the condition kh≪1 (k is the acoustic wavenumber, h is the rms surface height) is insufficient to guarantee the accuracy of first-order (or higher-order) perturbation theory. When the surface correlation length l becomes too large or too small with h held fixed, higher-order perturbation terms can make larger contributions to the scattering cross section than lower-order terms. An explanation for this result is given. The regions of validity for low-order perturbation theory are also given. These results resolve (for the Gaussian roughness spectrum) the long-standing discrepancy between the first-order perturbation cross section and the cross section obtained with the Kirchhoff approximation for conditions when both approximations have generally been considered accurate. It is shown explicitly that, for some cases, the Kirchhoff prediction is the correct one. Finally, it is found that the perturbation expansion for the scattering cross section reduces to a power series expansion in the rms slope s when kl≪1. This observation provides additional insight into the connection between the small slope assumption and the validity of low-order perturbation theory.
Analysis of the time spread of bottom interacting signals from an abyssal plain environment
Authors: Vidmar Paul J. , Knobles David P.
Published: October 2005

Measured and simulated signals from explosive sources are compared to determine some of the features of the time spread introduced by bottom interaction in an area having 200 m of sediment cover. Two types of time spreading are observed: (1) a short-duration (<0.2 s) primarily high-frequency time spread associated with paths reflected from the water–sediment interface and (2) a long-duration (>0.5 s) primarily low-frequency continuation of the measured signal beyond the termination of the simulated signal. The short-duration time spread is made up of a sequence of spikes and could be caused by interaction with layers in the upper part of the sediment. Scattering from the basalt beneath the sediment is consistent with the features of the long-duration time spread.
Linear and parametric array transmission across a water–sand interface—Theory, experiment, and observation of beam displacement
Authors: Williams K. L. , Satkowiak L. J. , Bugler D. R.
Published: October 2005

A series of measurements was made to investigate the effect of a water–sediment interface on the propagation of a bounded acoustic beam. The data obtained allowed mapping out of the sound-pressure field in a homogeneous sand sample for 20-kHz linear and parametric sources at several incident grazing angles. These results are compared with theoretical predictions calculated using the SAFARI model [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)]. The major results include: (1) absolute transmission levels and transmitted field structure; (2) demonstration that an attenuating liquid model of the sand sediment is adequate in theoretical modeling of the experiment and, as a by-product, experimental testing of the SAFARI program; (3) the conditions under which one may determine the transmitted field structure due to a truncated parametric array source by use of an incident Gaussian beam and the characteristics of that beam; and (4) the beam displacement at and below critical angle. Regarding the issue of beam displacement, it is found that the angular spectrum of a narrow beam, not its parametric nature, is responsible for the beam displacement at the critical angle as measured here. It is also shown that, when examining beam displacement, care must be taken to establish how it will be determined.
Free in-plane vibrations of a ring–spoke mechanical system
Authors: Filipich C. P. , Rosales M. B. , Jouglard C. E.
Published: October 2005

The present paper deals with the analysis of the dynamic behavior of the structures described in the title. It is assumed that the spokes are symmetrically distributed and clamped at the ring center. The circumferential ring response is expressed in terms of a complete set of periodic functions. The elastodynamic behavior of the spokes is taken into account by replacing them with equivalent frequency-dependent springs. Use is made of Dirac delta, doublet functions, etc. It is demonstrated that taking into account symmetric properties of the structure results in a significant reduction of the order of the system of equations. The free vibration of several cases was studied numerically. Natural frequencies and mode shapes are presented.
Free, in-plane vibrations of circular rings with radial supports taking into account shear and rotatory inertia effects
Authors: Rossi Raul E. , Laura Patricio A. A.
Published: October 2005

Natural frequency coefficients and modal shapes corresponding to some of the lower modes of vibration of the structural systems described in the title are determined using a finite element algorithmic procedure.
Dynamic response of a prestressed, thick strip plate to an impulsive load
Authors: Nozawa N. , Chonan S.
Published: October 2005

This paper is concerned with the dynamic response of an infinitely long thick strip plate. The plate is simply supported at the edges and subjected to initial in-plane stresses parallel and perpendicular to the edges. It is excited by an impulsive line force. The solution is obtained on the basis of a thick plate theory that takes into account the effects of shear deformation and rotatory inertia. Governing equations are solved by applying the methods of the Laplace transform with respect to time and the Fourier transform with respect to an axial space variable. Numerical results are presented for plates subjected to a lateral load represented by a time function sin2 ωt. The displacement, bending moment, and dynamic coefficients (maximum dynamic displacement/static displacement, maximum dynamic bending moment/static bending moment) are calculated and shown graphically for several values of the parameters involved.
Experimental frequency spectra of ultrasound transmission through two-dimensional ensembles of trapped microbubbles
Authors: Wu Junru , Nyborg Wesley L.
Published: October 2005

The frequency spectra of transmission coefficients for ultrasound passing through a sheet of gas-filled micropores have been measured using incident waves with amplitudes up to 2.4×104 Pa. It is found that as the amplitude of the incident wave is increased, the peak frequency of transmission loss through the two-dimensional trapped-bubble ensemble shifts to lower values by as much as 47%. The experiments indicate that the shifting is caused by the net displacements of air–water–membrane triple-phase lines and the air loss of the trapped bubble, which are due to the radiation force and microbubble production produced by the incident wave. Results of the experiments and possible theoretical explanations are discussed.
Light diffraction by two spatially separated ultrasonic waves
Authors: Kwiek P.
Published: October 2005

A theoretical model of light diffraction by two sinusoidal and spatially separated ultrasonic waves of frequency ratio 1:n is presented. Experimental verification of the model is shown for ultrasonic waves having frequency ratio 1:1 and 1:2, and the agreement between results, both theoretical and experimental, is very good. The investigation was performed for the near- (Fresnel) and far- (Fraunhofer) fields of the light diffracted by two ultrasonic waves.
An upper bound on acoustic reflectivity, and the Rayleigh approximation
Authors: Lekner John
Published: October 2005

Reflection of plane acoustic compressional waves at a stratified transitional layer between two fluid media is treated by means of a nonlinear differential equation for the reflection amplitude. When the normal component of the wave vector divided by the local density changes monotonically, the reflectance is shown to be no greater than that at a sharp transition between the same two media (at the same angle of incidence). A related Riccati-type differential equation for the reflection amplitude leads to the Rayleigh (or weak-reflection) approximation. This approximation is simple, easy to evaluate, and works well at all wavelengths provided that the reflection is weak.
Sound propagation in a waveguide with finite thermal conduction at the boundary
Authors: Anderson M. J. , Vaidya P. G.
Published: October 2005

The modal theory of sound propagation in an acoustic waveguide is extended to include the effect of finite heat conduction at the boundaries. A thermal-impedance equation is derived that controls the conduction of heat from the acoustic medium to the waveguide boundary. The thermal impedance is characterized by a single dimensionless parameter that measures dynamic thermal impedance as it ranges continuously from infinitely conducting to fully insulated boundaries. The boundary-value problem in the waveguide is then solved for rigid, no-slip, and finite conducting boundaries. Perturbations from inviscid mode shapes and axial attenuation rates are calculated for the acoustic mode as well as the modal coefficients of the vorticity and entropy modes as they depend upon the thermal-impedance parameter. It is found that the dependence of the preceding quantities on the thermal-impedance parameter is described for the most part by one continuous function of this parameter.
Correction for an auditory periphery model
Authors: Covington C. David
Published: October 2005

Payton [K. L. Payton, J. Acoust. Soc. Am. 83, 145–162 (1988)] constructed a model of the auditory periphery including a simulation of basilar membrane (BM) mechanics based on the numerical solution of the differential equation relating membrane displacement to stapes velocity, membrane compliance, and membrane damping. Payton indicated that the model membrane length parameter was arbitrarily doubled to 5.0 cm in order to avoid what appeared to be reflections. Even with this compensation, Payton relied on the fact that the middle-ear model essentially removed frequency components significantly below 1000 Hz, thereby attenuating the reverse traveling waves before they reached the region of the basilar membrane being modeled. In using the model, an error in the basilar membrane simulation module was isolated due to a data mapping discrepancy. Correcting this error eliminates the spurious response, restores the model to physiological dimensions, improves the execution speed versus resolution trade-off in the membrane component, and corrects a phase error introduced to the model.
A sound-speed sensor for the measurement of total protein concentration in disposable, blood-perfused tubes
Authors: Schneditz Daniel , Kenner Thomas , Heimel Helmut , Stabinger Hans
Published: October 2005

The aim of this investigation was to develop a sensor containing a disposable measuring cell capable of measuring fluid shifts in blood-perfused circulation systems. Usually, the determination of fluid shifts in such systems is achieved by tracking the concentration of particles or solutes in the perfusate. Since acoustic properties of blood are closely related to the total protein concentration (TPC) of the sample, a new approach for the calculation of fluid shifts is made by the continuous measurement of sound speed. The measuring principle is based upon the evaluation of the propagation time of short acoustic pulses that are repeatedly transduced to the sample. The retransmission is triggered by means of a new type of delay line. The method stands out for its accuracy (better than 0.1 m/s) and for the short acoustic propagation path (5–10 mm). In order to develop the disposable measuring cell, the acoustic properties of porcine blood were determined at different hematocrits and TPC at temperatures ranging from 20–40 °C. The dependence of sound speed on temperature and on TPC is described by a polynomial. The new sensor was tested in vitro simulating mass shifts by adding a mass (Msaline) of isotonic saline solution to the circulating blood mass (M). The acoustic device containing the disposable cell proved capable of sensing mass fractions [Msaline/(M+Msaline)] in the order of 0.5 g/100 g.
Apparent auditory deprivation effects of late onset: The role of presentation level
Authors: Gatehouse Stuart
Published: October 2005

Silman and colleagues [J. Acoust. Soc. Am. 76, 1347–1362 (1984)] have reported an apparent effect of late auditory deprivation; this presents as loss of discrimination over time in the unaided ear of individuals using a single hearing aid fitted in middle age. In a replication of the basic effect, the influence of presentation level was examined in 24 monaurally aided subjects. The effect was reversed at presentation levels below about 75 dB SPL. The ear that is normally aided performs better at high presentation levels, while, at lower presentation levels, the converse is true. Thus it appears that a form of selective adjustment takes place in a particular part of the dynamic range, at least in ears with a dynamic range limited by a sensory hearing loss. If this interpretation is correct, there are important implications for research on perceptual learning and for the time course of evaluation in hearing aid provision.
Within- versus cross-channel mechanisms in detection of envelope phase disparity
Authors: Strickland Elizabeth A. , Viemeister Neal F. , Fantini Deborah A. , Garrison Margery A.
Published: October 2005

These experiments were designed to examine the mechanism of detection of phase disparity in the envelopes of two sinusoidally amplitude-modulated (AM) sinusoids. Specifically, they were performed to determine whether detection of envelope phase disparity was consistent with processing within a single channel in which the AM tones were simply added. In the first condition, with an 8-Hz modulation frequency, phase-disparity thresholds increased sharply with an initial increase in separation of the carrier frequencies. They then remained approximately constant when the separation was an octave or above. In the second condition, with carrier pairs of 1 and 2 kHz or 1 and 3.2 kHz and a modulation frequency of 8 Hz, thresholds were little affected as the level of one carrier was decreased relative to the other. With a modulation frequency of 128 Hz, for most subjects there was more of an effect of level disparity on thresholds. In the third condition, when the modulation frequency was 8 Hz, subjects showed relatively constant thresholds whether the signals were presented monotically, dichotically, or dichotically with low- and high- pass noise. Dichotic thresholds were typically higher than monotic when the modulation frequency was 128 Hz. These results suggest that it is not necessary to have information available within a single additive channel to detect envelope phase disparity. In certain circumstances, a comparison across channels may be used to detect such disparities.
The responses of models of ‘‘high-spontaneous’’ auditory-nerve fibers in a damaged cochlea to speech syllables in noise
Authors: Geisler C. Daniel
Published: October 2005

The responses of four high-spontaneous fibers from a damaged cat cochlea responding to naturally uttered consonant–vowel (CV) syllables [m], [p], and [t], each with [a], [i], and [u] in four different levels of noise were simulated using a two-stage computer model. At the lowest noise level [+30 dB signal-to-noise (S/N) ratio], the responses of the models of the three fibers from a heavily damaged portion of the cochlea [characteristic frequencies (CFs) from 1.6 to 2.14 kHz] showed quite different response patterns from those of fibers in normal cochleas: There was little response to the noise alone, the consonant portions of the syllables evoked small-amplitude wide-bandwidth complexes, and the vowel-segment response synchrony was often masked by low-frequency components, especially the first formant. At the next level of noise (S/N=20 dB), spectral information regarding the murmur segments of the [m] syllables was essentially lost. At the highest noise levels used (S/N=+10 and 0 dB), the noise was almost totally disruptive of coding of the spectral peaks of the consonant portions of the stop CVs. Possible implications of the results with regard to the understanding of speech by hearing-impaired listeners are discussed.
AP threshold elevation in the guinea pig following exposure to a broadband noise
Authors: Grenner Jan , Nilsson Per , Katbamna Bharti
Published: October 2005

Sixty guinea pigs were exposed to a steady-state broadband noise with a falling frequency spectrum. The sound-pressure level was varied between 96 and 117 dB SPL, and the duration of the exposure was varied from 3 to 12 h. After 4–5 weeks, the auditory thresholds were determined by electrocochleography at 14 frequencies, and the results were compared with a control group. With increasing sound-pressure level, the thresholds became elevated at all frequencies. The maximum threshold elevation also exhibited a slight shift toward higher frequencies. With increasing exposure time, the threshold elevations increased and shifted into the high-frequency region, whereas the low-frequency region was less affected. Linear regression analysis showed that the average threshold elevation between 1 and 20 kHz did not deviate from that predicted by the equal-energy hypothesis. However, the high-frequency loss at 5–20 kHz was very dependent on the exposure time, whereas the 1- to 4-kHz loss was not. There was no sign of any critical intensity with sudden increments in threshold elevation.
Aerial propagation of spherical sound waves in bounded spaces
Authors: Lemire G. , Nicolas J.
Published: October 2005

The idea of using the method of complex image sources to model spherical sound-wave propagation in bounded spaces is reexamined in the light of the work of Gensane and Santon [J. Sound Vib. 63, 97–108 (1979)]. Use has been made of recent progress in the field of spherical sound-wave reflection. Calculations have been carried out in three simple spaces: a space limited by two infinite parallel planes (layer), a rectangular waveguide, and a rectangular enclosure. The results of predictions by the image-source method are compared to those of wave theory for frequencies from 60 to 1000 Hz in spaces whose characteristic dimension ranges from 0.7 to 11 m. The results indicate that the image-source model generally agrees within a few tenths of a dB with the wave theory in the cases of the layer, rectangular waveguide, and rectangular enclosure. The agreement between the two models is somewhat worse when the source-to-receiver distance is large compared with the dimension of the space, and when the source is close to a highly absorbent edge of the space. Except for these extreme cases, the complex image-source method is a valuable tool for studying the propagation of sound in bounded spaces, even at low frequencies in the audio range.
Determination of compressional wave speed profiles using modal inverse techniques in a range-dependent environment in Nantucket Sound
Authors: Frisk George V. , Lynch James F. , Rajan Subramaniam D.
Published: October 2005

An inverse method for determining geoacoustic properties in a horizontally stratified, shallow-water waveguide is extended to the case of a weakly range-dependent environment. The technique consists of estimating the local modal eigenvalues from the beam-formed output of a horizontal array and using these data as input to modal inverse methods for obtaining the local bottom parameters. Specifically, the approach is applied to data at 140 and 220 Hz obtained in a shallow-water environment with a known abrupt change in bathymetry. First, a range-independent medium is assumed, and both iteration of forward models and perturbative inversion methods are applied to the modal data to obtain estimates of the bottom sound velocity profile. Although the perturbative inversion results are clearly superior, neither approach reproduces the full dependence with range of the observed pressure fields or the complete modal peak structure. In particular, the data exhibit an apparent splitting of the modal peaks which is interpreted, within the context of adiabatic mode theory, as the superposition of the modal contributions from the two segments of the waveguide with differing depths. When the assumption of a range-independent medium is relaxed, and the perturbative inverse technique is applied to the eigenvalue data from each portion of the waveguide, distinctly different bottom profiles are obtained for each part. These result in significantly improved agreement between theory and experiment, thereby demonstrating the effectiveness of the range-dependent inversion procedure.
Interaction of sound waves. Part IV: Scattering of sound by sound
Authors: Berntsen Jarle , Naze Tjo/tta Jacqueline , Tjo/tta Sigve
Published: October 2005

A theory for the nonlinear interaction between two sound beams produced by real sources in a lossless fluid was presented in a previous work [Naze Tjo/tta and Tjo/tta, J. Acoust. Soc. Am. 83, 487–495 (1988)]. A general solution of the governing equation in the quasilinear approximation, valid at any range, crossing angle, and frequency ratio, was obtained for prescribed boundary conditions. An asymptotic formula for the sum and difference frequency sound pressure was obtained at large distance from the sources. It relates the amplitude and directivity of the sound field in the farfield to the on-source conditions. In the present work, the theory is further developed, and numerical results are presented for uniform piston and Gaussian sources. The influence of source geometry (separation, and intersection angles from 0° to 90°) and frequency on the beam pattern of the nonlinearly generated sound is studied. The results obtained are related to earlier works on scattering of sound by sound, which are discussed. Necessary conditions are also given to determine when scattering of sound by sound can be observed. In the special case of thin Gaussian beams intersecting at a small angle, the results are compared with that obtained by Darvennes and Hamilton [submitted to J. Acoust. Soc. Am.] using the paraxial approximation. Also discussed are some properties of the automatic global adaptive quadrature routine used to compute the two-dimensional integral in the asymptotic formula.
The rheology of an anelastic medium studied by means of the observation of the splitting of its eigenfrequencies
Authors: Caputo Michele
Published: October 2005

It is seen how the rheology of anelastic media causes a splitting of each of the free modes of an oscillator into a number of lines spread over a frequency band depending on the type of rheology. The experimental identification of these lines and/or of the width of each multiplet allows the retrieval of the rheological properties of the medium.
Elastodynamic diffraction correction integrals
Authors: Sedov Alexander , Schmerr Lester W.
Published: October 2005

Elastodynamic models are developed for predicting the diffraction correction integrals of contact compressional and shear wave transducers. Explicit high-frequency diffraction corrections are obtained and compared with analogous fluid-model predictions. It is demonstrated that, at sufficiently high frequencies, these elastodynamic models predict first-order diffraction correction integrals that are identical in form to the Lommel integrals for fluid media. The differences between the elastodynamic and fluid models are also demonstrated explicitly in the farfield.
Block diagram modeling of tall, thin parallelepiped piezoelectric structures
Authors: Hayward Gordon , Gillies Dean
Published: October 2005

A model is presented for predicting the behavior of tall, thin piezoelectric transducer elements, typical of those encountered in phased or linear array assemblies. Based on a block diagram, systems feedback approach, the model is amenable to computer implementation as well as satisfying intuitive and physical constraints. The method permits a ready understanding of electrical, piezoelectric, and mechanical coupling that occurs when two, loosely coupled vibrational modes are present within a transducer structure. A range of experimental and theoretical results, including impedance and pulse-echo characteristics, is presented for different transducer configuration ratios. Provided that the constraint of twin, compressional modes of vibration is satisfied, the model is shown to predict the principal resonance features with an accuracy ranging from 1%–5.2%.
Context effects in recognizing syllable-final /z/ and /s/ in different phrasal positions
Authors: Gordon Peter C.
Published: October 2005

An examination of the effect of phrase-final lengthening on the temporal correlates of voicing in syllable-final /s/ and /z/ was conducted. Discriminant analyses revealed that a combination of vowel duration, frication duration, and the duration of simultaneous voicing and frication was quite successful in determining voicing independently of phrase-final lengthening. Two perceptual experiments revealed that human listeners’ recognition of the segments does benefit from hearing the syllables in sentential context as opposed to when they are excised from context and presented in isolation. The benefit was greatest for /s/ in phrase-final position and /z/ in phrase-internal position. This suggests that the presence of sentential context allows listeners to factor out the influence of phrase-final lengthening on vowel duration and to more accurately interpret this cue to voicing of the final fricative. These findings extend previous results on rate-dependent processing of overall speaking rate to the processing of local speaking rate. By doing so, they provide further evidence of the importance of extended phonetic context in speech recognition.
Fast-moving average recursive least-mean-squares fit
Authors: Ng Lawrence C. , LaTourette Robert A. , Siconolfi Adam
Published: October 2005

A new approach is developed to reduce the computational complexity of a moving average least-mean-squares fit (LMSF) procedure. For a long data window, a traditional batch approach would result in an order N number of operations, where N is the window length. This study shows that the moving average batch LMSF procedure could be made equivalent to a recursive process with identical filter memory length, but at an order of reduction in computation load. The increase in speed due to reduce computation could make the moving average LMSF procedure competitive for many real-time processing applications.
Probability density approximations of linear system responses to intensity-modulated Gaussian processes
Authors: Mark William D.
Published: October 2005

An intensity-modulated Gaussian process {x(t)} is defined as the product of a non-negative stationary random process {σx(t)} and a stationary Gaussian process {z(t)} that is statistically independent of {σx(t)}. When such an intensity-modulated process is the excitation to a linear time-invariant system, the response process {y(t)}, conditioned on the excitation-modulating function σx(t), is a generally nonstationary Gaussian process. This property is used to develop an approximation to the probability density function (PDF) of the system response by assuming that the time-varying conditional response variance σ2y(t), conditioned on the excitation-modulating function σx(t), is governed by the gamma PDF. The resulting response process PDF is characterized by two parameters: the mean and variance of the conditional response variance σ2y(t). An alternative approximation to the response PDF, characterized by these same two parameters, is developed by using a Taylor’s series representation in the variable σ2y of the response PDF conditioned on σ2y. This latter PDF approximation is shown to be identical to the Gram–Charlier series of type A through terms involving the Hermite polynomial of degree 6. The two response PDF approximations are shown to give essentially identical results for values of the coefficient of variation of σ2y of one-half or less. Simple, easily evaluated expressions for the mean and variance of σ2y are derived in terms of measurable quantities by utilizing the assumption that fluctuations in σx(t) occur slowly in comparison with those of z(t).