bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of auditory-filter bandwidths at 2 kHz in young normal listeners
Authors: Moore Brian C. J.
Published: October 2005

Auditory-filter shapes at 2 kHz were estimated for 95 young normally hearing subjects using a notched-noise masker with spectrum level of 45 dB. Excluding two subjects with a recent history of noise exposure, the equivalent rectangular bandwidths (ERBs) of the filters were approximately normally distributed but the distribution had a slight positive skew. The mean ERB was 308 Hz and the standard deviation was 32 Hz. The two noise-exposed subjects had ERBs of 404 and 497 Hz.
Jump phenomena in coupled Duffing oscillators under random excitation
Authors: Jia Wenyao , Fang Tong
Published: October 2005

Jump phenomena in coupled Duffing oscillators under random excitations are analyzed by the Gaussian closure moment method. It is found that multilevel mean-square responses can occur when the bandwidth of the random excitation is sufficiently narrow. If the resonance zones of the oscillators overlap each other, both the mean-square responses will jump significantly, but in opposite directions.
Backprojection reconstruction of random source distributions
Authors: Norton Stephen J. , Linzer Melvin
Published: October 2005

A new approach to reconstructing intensity images of random source distributions is described. The technique requires multiple detecting transducers surrounding the source region, and employs a filtered-backprojection algorithm, similar in principle to that used in x-ray tomography, to process the detected source radiation. The detected signals from transducer pairs are cross correlated prior to backprojection. We derive the point-spread function of the source reconstruction algorithm for random and spatially incoherent sources. Under these conditions, the imaging approach is linear in source intensity and is capable, in principle, of reconstructing quantitative images of extended and complex source intensity distributions. Moreover, source images can be recovered under much lower signal-to-noise conditions than those required by traditional source location schemes, such as triangulation. Backprojection formulas are presented for both the two- and three-dimensional inverse-source problems, although the analysis is carried out in detail for the former case only. Simulations are presented which demonstrate the reconstruction algorithm in the absence of noise and under conditions of significant receiver noise. The backprojection/cross-correlation algorithm is shown to be effective in extracting source images from noise even when the assumptions of source randomness and spatial incoherence are violated.
Asymptotic optimization of multilevel quantization for a signal processing system containing an OR-ing device
Authors: Al-Hussaini Emad K.
Published: October 2005

In previous studies, performance models were developed for a system composed of quantizers followed by an OR-ing device and an accumulator. In this article, a method is presented to determine the breakpoints and the levels of the quantizer by maximizing the detector efficacy. Asymptotic and finite sample performances are presented and compared with the previous results. In order to improve the performance of the asymptotic detector for the finite sample case, a slight modification is suggested while maintaining a reasonable asymptotic performance.
Signals for optimum bandlimited system interrogation with application to underwater acoustics
Authors: Bold Gary E. J. , Johns Murray D. , Birdsall Theodore G.
Published: October 2005

Consideration of the bandlimited system interrogation problem together with a reasonable definition of a measurement signal-to-noise ratio leads to a figure of merit for interrogation signals. Both time and frequency domain characteristics of the signal are important. Several candidate classes of interrogating signals are described and compared. Stepped frequency chirps are found to combine nearly ideal properties with ease of generation. An illustration of the use of stepped frequency chirps in an underwater acoustic experiment is given.
The use of CHIEF to obtain unique solutions for acoustic radiation using boundary integral equations
Authors: Seybert A. F. , Rengarajan T. K.
Published: October 2005

This article is concerned with the problem of obtaining a unique solution for radiation and scattering problems at characteristic wavenumbers when a boundary integral equation formulation is used. It is shown that the combined Helmholtz integral equation formulation (CHIEF) method works even when numerous interior points lie exactly on nodal surfaces of a mode corresponding to an eigenfrequency of the related interior problem, when at least one interior point does not lie on a nodal surface. CHIEF is compared to the Helmholtz gradient formulation (HGF) for circumventing nonuniqueness and is found to yield a more accurate solution. A procedure is used to indicate the solution error when using integral equation methods, with or without a technique to circumvent nonuniqueness. This procedure uses the velocity potential of an interior point as an indicator of solution error. In all cases considered, the interior potential correctly indicated a good or bad solution; whereas the matrix condition number falsely indicated a bad solution in several instances.
A numerical study of thermal effects on nonlinear bubble oscillations
Authors: Miksis Michael J. , Ting Lu
Published: October 2005

An integral-differential system was derived by Miksis and Ting describing the nonlinear oscillations of a gas bubble including thermal and viscous effects. Here, an efficient numerical scheme is presented to solve this system for long times relative to the forcing period. Examples are presented and compared with the Rayleigh–Plesset equation, which has no thermal damping. Numerical results show that the initial free oscillations are damped out much faster when thermal damping is included. Also shown is the fact that it is possible for a bubble to have its mean radius grow slowly with time. In this case for large time the bubble will approach a new constant mean radius, which is larger than the initial equilibrium radius. For the special case of small amplitude forcing, asymptotic periodic solutions for very large time are constructed and a method to systematically derive the higher-order terms is demonstrated.
Impulse propagation in a neutral atmosphere
Authors: Don C. G. , Cramond A. J.
Published: October 2005

Computer simulation studies are presented for the propagation of an impulsive sound over a uniform impedance boundary in the presence of a neutral atmosphere. Based on typical explosive and gunfire waveforms, results from two levels of approximation arising from continuous wave propagation theory are compared and the simpler equation, involving just the plane-wave reflection coefficient and the boundary loss factor, is found to be adequate over a range of source–receiver geometries. The effect of changing the impulse shape and the ground impedance is discussed by considering the frequency dependence of the effective image source and, in particular, on the ground wave contribution to this source. A brief comparison is made between the predictions and measurements using two different duration impulses.
Numerical modeling of acoustic tomography in the Straits of Florida: Sensitivity to bathymetry
Authors: Nghiem-Phu Lan , DeFerrari Harry A.
Published: October 2005

An acoustic model based on the split-step parabolic equation technique is used to study the effects of irregularities in bathymetry on the transmission loss or equivalently, sound energy distribution for continuous wave (cw) acoustic signals. In particular, contours of transmission loss in the range-depth plane are predicted for the propagation of a 510-Hz cw signal across the Straits of Florida between Miami, Florida and Bimini, Bahamas. The predicted intensity contours exhibit recognizable energy bundles that correspond to actual ray bundles. The stability of these bundles is studied as random bottom irregularities are introduced. The distribution of acoustic energy is found to be insensitive to random variations in bottom bathymetry of up to 5 m rms. The same model is used to investigate the feasibility of transport and depth-averaged temperature measurements of the Florida current by acoustic method. Energy contour plots are predicted for several source–receiver geometries. A system of five transceivers positioned to form two triangles sharing a common vertex in the eastern edge of the Miami terrace is evaluated as a monitoring strategy.
A model for the propagation of short pulses of ultrasound in a solid
Authors: Weight John P.
Published: October 2005

A simple model has been introduced which allows calculations to be made of the particle displacement and velocity waveforms which arise when short pulses of ultrasound are radiated into solid media from transducers typical of those used in nondestructive evaluation. The model makes use of the plane- and edge-wave nature of the pulses radiated and, for simplicity, incorporates an empirical extension of the impulse response method for propagation in a fluid medium. Calculations made using the model are compared with other theoretical results obtained previously by harmonic synthesis, as well as with experimental measurements of pulse waveforms made using a miniature piezoelectric receiving probe. The results obtained are of particular relevance to the characterization of small targets using ultrasound.
Direct and inverse scattering for viscoelastic media
Authors: Ammicht E. , Corones J. P. , Krueger R. J.
Published: October 2005

A time domain approach to direct and inverse scattering problems for one-dimensional viscoelastic media is presented. Such media can be characterized as having a constitutive relation between stress and strain which involves the past history of the strain through a memory function, the relaxation modulus. In the approach in this article, the relaxation modulus of a material is shown to be related to the reflection properties of the material. This relation provides a constructive algorithm for direct and inverse scattering problems. A numerical implementation of this algorithm is tested on several problems involving realistic relaxation moduli.
An impulse response method to evaluate time-dependent acoustic radiation loading on elastic vibrators
Authors: Ebenezer D. D. , Stepanishen Peter R.
Published: October 2005

A general method is presented to determine the time-dependent acoustic radiation loading on fluid-loaded elastic vibrators via an impulse response approach. The method is based on the use of a time-dependent in vacuo modal expansion for the velocity of the vibrator. The time-dependent pressure on the vibrator is expressed as a modal expansion in which each modal pressure is a sum of time convolutions involving the modal velocities and self- and interaction impulse responses. Fourier transform methods are used to relate the impulse responses to the usual radiation impedances. Numerical results showing the self and interaction impulse responses for special cases of one-dimensional plates and cylinders of finite length are presented.
Rayleigh wave propagation in deformed orthotropic materials
Authors: Delsanto P. P. , Clark A. V.
Published: October 2005

A perturbation method is described for the investigation of the propagation of Rayleigh waves on the surface of a homogeneous anisotropic initially deformed material plate. Our perturbation formalism is quite general and can also be applied when other small effects, like slight temperature changes or external magnetic fields, affect the Rayleigh wave propagation velocity. The special cases of slight orthotropy and initial deformations are analyzed in detail. For these cases we derive the Rayleigh wave phase velocity as a function of the propagation direction, the elastic constants, and the initial stresses. The linearity of our formulas suggests that Rayleigh waves can be conveniently used as an experimental technique for the solution of the inverse problem of determining the elastic constants and/or the initial stresses in a material.
The sound of two hands clapping: An exploratory study
Authors: Repp Bruno H.
Published: October 2005

Clapping is a little-studied human activity that may be viewed either as a form of communicative group behavior (applause) or as an individual sound-generating activity involving two ‘‘articulators’’—the hands. The latter aspect was explored in this pilot study by means of acoustical analyses and perceptual experiments. Principal components analysis of 20 subjects’ average clap spectra yielded several dimensions of interindividual variation that were related to observed hand configuration. This relationship emerged even more clearly in a similar analysis of a single clapper’s deliberately varied productions. In perception experiments, subjects proved sensitive to spectral properties of claps: For a single clapper, at least, listeners were able to judge hand configuration with good accuracy. Besides providing some general information on individual variations in clapping, the present results support the general hypothesis that sound emanating from a natural source informs listeners about the changing states of the source mechanism.
Gap detection and the auditory filter: Phase effects using sinusoidal stimuli
Authors: Shailer Michael J. , Moore Brian C. J.
Published: October 2005

Psychometric functions were determined for the detection of temporal gaps in sinusoidal signals at center frequencies between 0.2 and 2.0 kHz. A continuous notched-noise masker was used to restrict listening to the signal frequency region. The gap always started when the signal was at a positive-going zero crossing. There were three different conditions for the starting phase of the signal at the termination of the gap. In the standard-phase condition the signal restarted at a positive-going zero crossing, in the reversed-phase condition at a negative-going zero crossing, and in the preserved-phase condition at the phase the signal would have had if the gap had not been present. In the standard-phase and reversed-phase conditions the psychometric functions were nonmonotonic, showing oscillations with a period equal to that of the signal; maxima in the functions for the standard-phase condition coincided with minima in the functions for the reversed-phase condition, and vice versa. In the preserved-phase condition the psychometric functions were monotonic and the 75% points were roughly independent of center frequency, having a value of about 5 ms. The general form of the results can be modeled by a filter bank followed by a square-law device and a temporal integrator, but good agreement between the data and the model could not be attained across the whole range of gap durations. The deviations between data and model suggest that subjects are sensitive to the brief transitions in phase (or, equivalently, in frequency) in some conditions.
Effects of acoustic modification on consonant recognition by elderly hearing-impaired subjects
Authors: Gordon-Salant Sandra
Published: October 2005

In a recent study [S. Gordon-Salant, J. Acoust. Soc. Am. 80, 1599–1607 (1986)], young and elderly normal-hearing listeners demonstrated significant improvements in consonant–vowel (CV) recognition with acoustic modification of the speech signal incorporating increments in the consonant–vowel ratio (CVR). Acoustic modification of consonant duration failed to enhance performance. The present study investigated whether consonant recognition deficits of elderly hearing-impaired listeners would be reduced by these acoustic modifications, as well as by increases in speech level. Performance of elderly hearing-impaired listeners with gradually sloping and sharply sloping sensorineural hearing losses was compared to performance of elderly normal-threshold listeners (reported previously) for recognition of a variety of nonsense syllable stimuli. These stimuli included unmodified CVs, CVs with increases in CVR, CVs with increases in consonant duration, and CVs with increases in both CVR and consonant duration. Stimuli were presented at each of two speech levels with a background of noise. Results obtained from the hearing-impaired listeners agreed with those observed previously from normal-hearing listeners. Differences in performance between the three subject groups as a function of level were observed also.
Frequency map of the spiral ganglion in the cat
Authors: Keithley Elizabeth M. , Schreiber Rebecca Cronin
Published: October 2005

A frequency map of the cat spiral ganglion has been determined on the basis of reconstructed cochleas in which individual spiral ganglion cells were labeled with horseradish peroxidase following determination of their characteristic frequency; the cochleas were the same as those used by Liberman and Oliver [J. Comp. Neurol. 223, 163–176 (1984)]. By matching this map to one previously described for the organ of Corti [M. C. Liberman, J. Acoust. Soc. Am. 72, 1441–1449 (1982)], an estimate of the afferent innervation density of the inner hair cells was derived. Counts of myelinated nerve fibers at the habenula perforata and inner hair cells were also performed and yielded similar results in all but the most basal 10%–15% of the cochlea. Between 0.1 and 20 kHz there is a gradual monotonic increase as a function of frequency in the number of spiral ganglion cells terminating on each inner hair cell, from about eight ganglion cells per inner hair cell to about 30 ganglion cells per inner hair cell. Above 20 kHz, it seems there is a decrease to about ten ganglion cells per inner hair cell. The greatest innervation density is at approximately the region of the basilar membrane with the greatest density of inner hair cells per millimeter.
Correlation between time functions of sound pressure, masking, and OAE suppression
Authors: Zwicker E. , Scherer A.
Published: October 2005

Periodic sound-pressure time functions with frequency components below 50 Hz were used to measure within their period (a) the temporal course of masking, called a masking-period pattern (MPP), and (b) the temporal course of suppression of delayed evoked otoacoustic emissions, called a suppression-period pattern (SPP). Three different time functions were used: an alternating Gaussian impulse, its first integral, and its second integral. In each case, the course of the SPP is a mirror image of that of the MPP: Small masking corresponds to small suppression, while strong masking coincides with almost total suppression. Since otoacoustic emissions are assumed to have their origin in the inner ear, it can be argued that simultaneous masking, an effect including central processing, is very strongly based on peripheral processes located in the cochlea. Both MPP and SPP are closely related to the second derivative of the sound-pressure time function.
Wheel/rail rolling noise, I: Theoretical analysis
Authors: Remington Paul J.
Published: October 2005

A comprehensive analytical model of the wayside noise generated by a railroad wheel rolling on straight track is presented. The model assumes that the small-scale roughness on the running surfaces of the wheel and rail is the primary mechanism for the noise generation. Included in the model are such effects as the spatial filtering of the roughness due to the finite area of contact between the wheel and rail; the interaction between the wheel and rail, including local contact stiffness; axial response of the wheel; the radiation efficiencies of the wheel and rail; and the influence of sound propagation, including finite ground impedance.
Beamforming of a distorted line array in the presence of uncertainties on the sensor positions
Authors: Bouvet Michel
Published: October 2005

Array processing based on a linear assumption implies degradations in the source bearing estimation when the array is not linear, which is the usual case in real-world problems. Assuming only that the array is planar (but not necessarily quasilinear), we describe a method to include in an adaptive way information about the sensor locations into the array processing, in order to take into account its geometrical shape. This information can be the relative positions of the sensors given by a mechanical device included in the array. The relative sensor positions can also be estimated using a source with a known bearing, a cooperative target for example. Simulation results in a real underwater noise sample show that these two cases lead to important improvement with respect to the classical array processing, based on a linear assumption, provided that the signal-to-noise ratio of the known source is high enough (around 10 dB in our example).
Tone-burst-evoked otoacoustic emissions from normal-hearing subjects
Authors: Norton Susan J. , Neely Stephen T.
Published: October 2005

Tone-burst-evoked otoacoustic emissions were measured as a function of tone-burst sound pressure level and frequency in normally hearing ears. Although the spectral and temporal properties varied across individual ears, there was a close correspondence between stimulus and response spectra. Both the spectral and latency characteristics of tone-burst-evoked emissions are consistent with the hypothesis that they are generated at sites along the cochlear partition corresponding to their frequency.
The temporal course of masking and the auditory filter shape
Authors: Moore Brian C. J. , Poon Paul W. F. , Bacon Sid P. , Glasberg Brian R.
Published: October 2005

Recent experiments have shown that frequency selectivity measured in tone-on-tone simultaneous masking improves with increasing delay of a brief signal relative to the onset of a longer duration gated masker. To determine whether a similar improvement occurs for a notched-noise masker, threshold was measured for a 20-ms signal presented at the beginning, the temporal center, or the end of the 400-ms masker (simultaneous masking), or immediately following the masker (forward masking). The notch width was varied systematically and the notch was placed both symmetrically and asymmetrically about the 1-kHz signal frequency. Growth-of-masking functions were determined for each temporal condition, for a noise masker without a spectral notch. These functions were used to express the thresholds from the notched-noise experiment in terms of the level of a flat-spectrum noise which would produce the same threshold. In simultaneous masking the auditory filter shapes derived from the transformed data did not change significantly with signal delay, suggesting that the selectivity of the auditory filter does not develop over time. In forward masking the auditory filter shapes were sharper than those for simultaneous masking, particularly on the high-frequency side, which was attributed to suppression.
Growth of masking as a measure of response growth in hearing-impaired listeners
Authors: Stelmachowicz Patricia G. , Lewis Dawna E. , Larson Lori L. , Jesteadt Walt
Published: October 2005

Growth-of-masking functions were obtained from 19 normal and 5 hearing-impaired listeners using a simultaneous-masking paradigm. When masker and probe frequency are identical, the slope of masking approximates 1.0 for both normal-hearing and impaired listeners. For masker frequencies less than or greater than probe frequency, the slopes for impaired listeners are shallower than those of normals. These findings are consistent with previously reported physiological data (single-fiber rate versus level and AP masking functions) for animals with induced cochlear lesions. Results are discussed in terms of a potential masking technique to estimate the growth of response in normal and impaired ears.
The profile-analysis bandwidth
Authors: Bernstein Leslie R. , Green David M.
Published: October 2005

Detection of a change in spectral shape, or profile analysis, appears to be mediated by comparisons across widely separated frequency ‘‘channels’’ rather than by local comparisons among adjacent frequency regions [e.g., Green et al., J. Acoust. Soc. Am. 73, 639–643 (1983)]. Two experiments were conducted in order to determine the ‘‘resolution bandwidth’’ of these channels. The first involved detection of an increment to a single component of a multicomponent background as a function of the number of components in the background. Performance improved as the number of components was increased from 3 to 21. Further increases yielded poorer performance and the estimate of the ‘‘resolution bandwidth’’ from these data suggests that this poorer performance was due simply to masking. The second experiment involved discrimination of a multicomponent complex having a flat amplitude spectrum from one having a sinusoidally ‘‘rippled’’ amplitude spectrum. The latter experiment yielded somewhat larger estimates of the ‘‘resolution bandwidth’’ than did the former. Finally, profile analysis was investigated under a dichotic condition that precluded peripheral masking of the signal. Our results, like those of Green and Kidd [J. Acoust Soc. Am. 73, 1260–1265 (1983)], suggest that, although spectral analysis can be achieved using information across ears, performance is inferior to that obtained with diotic stimuli.
Infant speech-sound discrimination testing: Effects of stimulus intensity and procedural model on measures of performance
Authors: Nozza Robert J.
Published: October 2005

Performance of infants in a speech-sound discrimination task (/ba/ vs /da/) was measured at three stimulus intensity levels (50, 60, and 70 dB SPL) using the operant head-turn procedure. The procedure was modified so that data could be treated as though from a single-interval (yes–no) procedure, as is commonly done, as well as if from a sustained attention (vigilance) task. Discrimination performance changed significantly with increase in intensity, suggesting caution in the interpretation of results from infant discrimination studies in which only single stimulus intensity levels within this range are used. The assumptions made about the underlying methodological model did not change the performance–intensity relationships. However, infants demonstrated response decrement, typical of vigilance tasks, which supports the notion that the head-turn procedure is represented best by the vigilance model. Analysis then was done according to a method designed for tasks with undefined observation intervals [C. S. Watson and T. L. Nichols, J. Acoust. Soc. Am. 59, 655–668 (1976)]. Results reveal that, while group data are reasonably well represented across levels of difficulty by the fixed-interval model, there is a variation in performance as a function of time following trial onset that could lead to underestimation of performance in some cases.
Effects of hearing loss on utilization of short-duration spectral cues in stop consonant recognition
Authors: Dubno Judy R. , Dirks Donald D. , Schaefer Amy B.
Published: October 2005

The purpose of this experiment was to evaluate the utilization of short-term spectral cues for recognition of initial plosive consonants (/b,d,g/) by normal-hearing and by hearing-impaired listeners differing in audiometric configuration. Recognition scores were obtained for these consonants paired with three vowels (/a,i,u/) while systematically reducing the duration (300 to 10 ms) of the synthetic consonant–vowel syllables. Results from 10 normal-hearing and 15 hearing-impaired listeners suggest that audiometric configuration interacts in a complex manner with the identification of short-duration stimuli. For consonants paired with the vowels /a/ and /u/, performance deteriorated as the slope of the audiometric configuration increased. The one exception to this result was a subject who had significantly elevated pure-tone thresholds relative to the other hearing-impaired subjects. Despite the changes in the shape of the onset spectral cues imposed by hearing loss, with increasing duration, consonant recognition in the /a/ and /u/ context for most hearing-impaired subjects eventually approached that of the normal-hearing listeners. In contrast, scores for consonants paired with /i/ were poor for a majority of hearing-impaired listeners for stimuli of all durations.
The violin and its bridge
Authors: Trott W. James
Published: October 2005

Single frequency measurements are obtained for the driving point admittance of a violin at three positions on the top of the bridge at directions parallel and normal to the top plate. Companion measurements of transfer admittance are taken from the top of the bridge to the body of the violin at the bridge feet. Phase measurements of the transfer admittance yield the phase relationship between the feet that indicates parallel or rocking motion of the bridge in its plane. These data are compared with data from other sources. The mechanical power input to the body of the instrument is calculated for an equivalent bow friction force.
Alternative spectral formulations for acoustic velocity measurement
Authors: Steyer Glen C. , Singh Rajendra , Houser Donald R.
Published: October 2005

The use of a multimicrophone acoustic intensity probe is investigated for the measurement of the acoustic velocity power spectrum. The conventional formulation [J. Acoust. Soc. Am. 73, 1047–1053 (1983)] for this measurement is found to be sensitive to measurement errors. Three alternative formulations of the velocity estimate are developed that are less sensitive to random error. The various formulations are implemented into a four-microphone probe for measurement of the three velocity components. Experiments in the nearfield of a piston and a periodically stiffened plate verify the predicted relative advantages of the various estimators.
Modeling of a dc glow plasma loudspeaker
Authors: Mazzola Michael S. , Molen G.Marshall
Published: October 2005

A plasma loudspeaker is a transducer that produces sound by means of an ionized gas channel rather than the voice coil of a conventional loudspeaker. Plasma loudspeakers characteristically have a flat frequency response at the higher acoustic frequencies because of their ‘‘massless’’ membrane; however, their low-frequency response is limited. In this article, a comprehensive model for the electrical and thermodynamic operation of the electrical discharge is presented that explains the frequency-dependent behavior of the discharge’s electrical impedance and acoustic response. The characteristic acoustic frequency response is shown to result from a spatial variation of the temperature relaxation time throughout the plasma channel due to the temperature dependence of that time constant. To support the model, electrical and sound-pressure level measurements in helium, argon, and air are presented.
The error in a narrow-band transfer function model prediction
Authors: Garrelick Joel M.
Published: October 2005

The error in narrow-band analytical or physical model predictions is estimated for the example of a harmonic force-driven rectangular plate. It is shown that a 5% uncertainty in input parameters defining structural dimensions, material properties, and source location may account for errors in a predicted transfer function exceeding 10 dB over a reasonably broad bandwidth. It is also shown that this error increases 6 dB per doubling of the (percent) uncertainty. These results imply that in the absence of incoherent averaging, either temporal, spatial, or ensemble, expectations for favorable comparisons of structural acoustic predictions among models, or between model and prototype, may often be unrealistic.
General formulas for the low-frequency acoustic scattering by a soft body or disk
Authors: Sabina Federico J.
Published: October 2005

The scattering problem of an incident plane sound wave by a soft arbitrarily shaped body as well as its allied diffraction problem by a disk is discussed. A first-class Fredholm integral equation is posed which, for low frequencies, yields a potential equations sequence for a wavenumber power solution expansion. The power solution expansion coefficients of the scattering cross section and the farfield amplitude up to O(κ6), where κ is the wavenumber, are found to be related through only a few low-order solutions of the above equations. Reciprocity relations between them were exploited. The following new general formulas are obtained. The scattering cross-section coefficient σ4 of O(κ4) is found in terms of three solutions up to O(κ2), rather than six solutions up to O(κ5). As for the farfield amplitude, the sixth (fifth, fourth, and third) coefficient of O(κ5) (κ4, κ3, and κ2) is related to only six (five, four, and two) solutions up to O(κ3) (κ2, κ, and κ). As an application of the above results, the coefficient σ4 is explicitly calculated using newly found solutions for an elliptic disk. Also, the circular disk results are shown for an arbitrary angle of incidence.
On the transition matrix for acoustic waves scattered by a multilayered inclusion
Authors: Yeh Yeong-Kae , Pao Yih-Hsing
Published: October 2005

The transition matrix (T matrix) for acoustic waves scattered by a multilayered inclusion with arbitrary geometry is reformulated by applying the Green’s identity for scalar wavefunctions. The derivation of the T matrix is much simpler than previous formulations based on the Helmholtz integral formula. Further simplification is accomplished by a new combination of basis functions for refracted waves. The final answer is different but can be reduced to previous results.
Acoustic power output from moving point singularities
Authors: Levine Harold , Candel Sébastien M.
Published: October 2005

This article provides theoretical results for the acoustic power output from point sources moving with an arbitrary subsonic speed along a general trajectory. Applications to steady and nonsteady rotational motions and to rectilinear and elliptical motions are presented. A harmonic analysis of the power output from one or more point sources in steady rotational motion is given, which includes an account of the distribution among individual modes at different speeds.
Solitary waves on nonlinear elastic rods. II.
Authors: Soerensen M. P. , Christiansen P. L. , Lomdahl P. S. , Skovgaard O.
Published: October 2005

In continuation of an earlier study of propagation of solitary waves on nonlinear elastic rods, numerical investigations of blowup, reflection, and fission at continuous and discontinuous variation of the cross section for the rod and reflection at the end of the rod are presented. The results are compared with predictions of conservation theorems for energy and momentum.
Attenuation of intense sinusoidal waves in air-saturated, bulk porous materials
Authors: Kuntz Herbert L. , Blackstock David T.
Published: October 2005

As intense, initially sinusoidal waves propagate in fluids, shocks form and excess attenuation of the wave occurs. We present data indicating that shock formation is not necessary for the occurrence of excess attenuation in nonlinear, lossy media, i.e., air-saturated, porous materials. An empirical equation is used to describe the excess attenuation of intense sinusoids in porous materials. The acoustic nonlinearity of and the excess attenuation in porous materials may be predicted directly from dc flow resistivity data. An empirical relationship is used to relate an acoustic nonlinearity parameter to the fundamental frequency and relative dc nonlinearity of two structurally different materials.
Wave propagation in media with three-dimensional quadratic refractive index profile
Authors: Jeng S. K. , Liu C. H.
Published: October 2005

This article presents a new method for studying wave propagation in an unbounded medium where the square of the refractive index is of a general three-dimensional quadratic form. By this method, the Green’s function can be expressed exactly by a onefold integral, for which the integrand is derived from a path integral. The numerical results for one-dimensional Green’s functions in linearly stratified media are first checked with those obtained from the well-known Airy function expressions. The method is then applied to obtain the three-dimensional Green’s functions for linear stratified media and for parabolic profiles with range-dependent (horizontal) variations. Some interesting phenomena caused by the horizontal variations (i.e., range dependence) of the medium will be shown and interpreted by simple ray pictures whenever appropriate. For the special case of a parabolic profile with symmetric turning points, a wave duct is formed and the Green’s function can be expanded as a series of wave modes. It will be shown that an evanescent mode in a purely stratified medium may switch to a propagating mode due to the range dependence of the medium property. Application of the results to acoustic wave propagation in the atmosphere and in the ocean will be discussed.
Effects of bottom attenuation on acoustic propagation with a modified ray theory
Authors: Siegmann W. L. , Jacobson M. J. , Law L. D.
Published: October 2005

The influence on ray propagation of including both attenuation and beam displacement at the bottom of a shallow-water isospeed channel is determined. Attenuation is incorporated using the Mackenzie-bottom model, rather than the commonly used Rayleigh reflection theory. Properties of displacement are studied as a function of launch angle and parameters such as bottom-to-water density, channel depth in wavelengths, and channel aspect ratio. Differences in beam displacement for the two bottom models are shown to affect the number and geometry of rays between surfaced source and receiver. Formulas for per-ray amplitude and phase shift and for incoherent total-field intensity are developed. Comparisons are made between these quantities for both modified and classical ray theory with a Mackenzie bottom, and also for both Mackenzie- and Rayleigh-bottom models using modified rays. Numerical computations show significant phase and amplitude differences arising in both types of comparisons.
Shallow water time-series simulation using ray theory
Authors: Westwood Evan K. , Tindle C. T.
Published: October 2005

Ray theory with beam displacement is used to simulate the propagation of pulses in shallow water. Comparisons show very close agreement between simulated time series and time series measured in an indoor tank having a sand bottom. The six normal modes present are successfully extracted from both the simulated and the experimental sets of depth-dependent time series. The ray model accounts for the frequency dependence of beam displacement by interpolating eigenray characteristics at three frequencies in the spectrum of the source pulse. Also, the model corrects ray theory when receivers are close to caustics formed by beam displacement, in which case eigenrays must be found at six frequencies. Mode theory phenomena such as mode cutoff and dispersion can be observed in the simulations produced by this method.
Comments on ‘‘A comparison of acoustical scattering from fluid-loaded elastic shells and sound soft objects’’ [J. Acoust. Soc. Am. 7
6, 1227 (1984)]
Authors: Veksler N. D.
Published: October 2005

Remarks concerning the physical mechanism of the acoustical pressure wave scattering by thin elastic spheroidal shells are given.
Reply to ‘‘Comments on ‘A comparison of acoustical scattering from fluid-loaded elastic shells and sound soft objects’ [J. Acoust. Soc. Am. 7
6, 1227 (1984)]’’
Authors: Werby M. F.
Published: October 2005

This letter to the editor is a reply to N. D. Veksler’s criticisms [J. Acoust. Soc. Am. 81, 777–779 (1987)] of the article ‘‘A comparison of acoustical scattering from fluid-loaded elastic shells and soft objects’’ [M. F. Werby and L. H. Green, J. Acoust. Soc. Am. 76, 1227–1230 (1984)].
Correspondence between acoustical scattering from spherical and end-on incident spheroidal shells
Authors: Werby M. F. , Green L. H.
Published: October 2005

Acoustical scattering from spherical shells has been studied extensively in the literature and is a highly developed and well-understood area. In contrast, scattering from nonspherical, three-dimensional objects has not been studied extensively due to theoretical and computational difficulties. The purpose of the work presented here is to study backscattered echoes (form functions) from submerged spheroidal elastic shells for end-on incident plane waves for several aspect ratios L/D and to compare the results with the well-studied spherical analog (L is the length and D the width of the object). The frequency range studied in terms of kL/2 (where k is the wavenumber of the incident field) goes from kL/2=3 to kL/2=15 and the aspect ratio varies from 1.5 to 3.0. Two values for shell thickness studied are for 0.1% and 1.0% of the semimajor axis, with the constraint that the inner surface of the shell is spheroidal. A remarkable similarity is noted between the form functions of the spheroids and the shells. This correspondence can be shown to be deduced from phenomenological expressions (due to Werby and Gaunard, ‘‘Proceedings of the 1985 Pressure Vessels and Piping Conference,’’ New Orleans, LA, 23–26 June 1985) for resonance locations and offers a simple means to predict the locations of end-on resonances for the more intractable problem of higher aspect ratio spheroids.
Acoustic refraction by a spark discharge in air
Authors: Lafleur L. Dwynn , Matese John J. , Spross Ronald L.
Published: October 2005

It is observed that, when the acoustic impulse from an electric spark is reflected normally from a rigid plate and detected after passage through the remains of the spark region, a precursor component appears in the received waveform. To explain this phenomenon in terms of refraction, a two-spark experiment is used to examine the acoustic properties of the post-discharge region near a spark gap. The measured times of arrival of the precursor signal are fitted to a simple lens model consisting of two parameters: lens radius and acoustic index of refraction. The temporal evolution of these lens parameters is also measured and interpreted in terms of a diffusion model. The diffusion coefficient characterizing the process is found to be much larger than that for thermal diffusion in air at room temperature. This is consistent with the much higher temperatures corresponding to the low acoustic index of refraction of the measured lens models.
Frequency effects in profile analysis and detecting complex spectral changes
Authors: Green David M. , Onsan Zekiye A. , Forrest Timothy G.
Published: October 2005

Seven experiments on the detectability of intensity changes in complex multitonal acoustic spectra are reported. Two general questions organize the experimental efforts. The first question is how the detectability of a change in a flat (equal energy) spectrum depends on the frequency region where a single intensive change is made. The answer is that frequency region plays a relatively minor role. Frequency changes in the midregion of the spectrum are the easiest to hear, but thresholds increase by only about 5 dB over the range from 200 to 5000 Hz. For all frequencies, the psychometric function is of the form d′=k(Δp), where k is a constant and Δp is the change in pressure. The second question is how can we predict the detectability of complex changes over the entire frequency range from the detectability of change at each separate region. Thresholds for detecting a change from a flat spectrum to a spectrum whose amplitude varies in sinusoidal (‘‘rippled’’) fashion over logarithmic frequency are measured at different frequencies of ripple. The thresholds are found to be independent of ripple frequency and are 7 dB higher than predicted on the basis of an optimum combination rule.
Auditory enhancement of changes in spectral amplitude
Authors: Summerfield Quentin , Sidwell Andrew , Nelson Tony
Published: October 2005

An auditory enhancement effect occurs when one component of a harmonic series is omitted for a few hundred milliseconds and then reintroduced: The reintroduced harmonic stands out perceptually. Three experiments are reported that studied a version of this effect in which several components of a harmonic series are enhanced to define the formants of a vowel. Using the accuracy of vowel identification to measure the prominence of the formant peaks in the effective auditory representation, forms of the effect were identified that are qualitatively similar to the incremental and decremental responses seen in primary auditory-nerve fibers. These results are compatible with an origin for the enhancement effect in peripheral auditory adaptation. However, an additional mechanism is required to account for the demonstration [Viemeister and Bacon, J. Acoust. Soc. Am. 71, 1502–1507 (1982)] that enhancement can involve a true gain in the frequency region of the reintroduced component. These effects demonstrate one way in which the auditory system may attenuate the prominence of background noises while preserving the ability to represent changes in spectral amplitude produced by newly arriving signals.
The effect of cross-spectrum correlation on the detectability of a noise band
Authors: Cohen Marion F. , Schubert Earl D.
Published: October 2005

An experiment was performed to study the interaction of two narrow-band noises having correlated temporal envelopes. The detection threshold of a 100-Hz-wide noise-band signal was measured at different center frequencies in the presence of a continuous 100-Hz-wide noise band having a center frequency of 1000 Hz. The two noise bands had either correlated or independent temporal envelopes. Measured signal detection thresholds are lower when the two noise bands are independent, but the magnitude of this difference is not a simple function of the frequency separation between the two noise bands.
Masking effects in binaural detection and interaural time discrimination
Authors: Koehnke Janet , Cohen Marion F.
Published: October 2005

This study was designed to investigate the effects of masker level and frequency on binaural detection and interaural time discrimination. Detection and interaural time discrimination of a 700-Hz sinusoidal signal were measured as a function of the center frequency and level of a narrow-band masking noise. The masker was a continuous, diotic, 80-Hz-wide noise that varied in center frequency from 250 to 1370 Hz. In the detection experiment, the signal was presented either diotically (NoSo) or interaurally phase reversed (NoSπ). In the interaural time discrimination experiment, the signal level needed to discriminate a 30-μs interaural delay was measured. As would be expected, the presence of the masker has a greater effect on NoSo detection than NoSπ detection, and for masker frequencies at or near the signal frequency. In contrast, interaural time discrimination can be improved by the presence of a low-level masker. Also, performance improves more rapidly as the signal/masker frequency separation increases for NoSo detection than for interaural time discrimination and NoSπ detection. For all three tasks, significant upward spread of masking occurs only at the highest masker level; at low masker levels, there is a tendency toward downward spread of masking.