bluuebunny/crossref_metadata_2025 huggingface dataset:
Free vibration of a thin spherical shell containing a compressible fluid
Authors: Bai Mingsian R. , Wu Kuorung
Published: October 2005

Free vibration of a thin spherical shell filled with a compressible fluid is investigated. The interactions at the interface between the elastic structure and the compressible fluid are taken into account. The objective of this study is to develop a hybrid numerical technique for the free vibration analysis of sound–structure interaction problems. The boundary element method is employed for modeling the acoustic disturbances in the cavity, while the finite element method is used for modeling the structural dynamics of the shell. The formulations are then combined into a coupled numerical scheme for the total pressure-displacement field. Natural frequencies and mode shapes are calculated by using the singular value decomposition algorithm. Physical insights into the resonance phenomena associated with sound–structure interactions are derived from the comparison between the results of the thin spherical shell, with and without the fluid loading effect.
Formulation of short-wavelength bistatically scattered fields in terms of monostatic returns
Authors: Junger Miguel C.
Published: October 2005

The relation between short-wavelength bi- and monostatically scattered fields of smooth scatterers, e.g., the sphere, is governed by the bistatic theorem. This relation is extended here to scatterers with marked edges, viz. finite cylinders and rectangular baffles. The formulation of the bistatic field in terms of the monostatic return does however depend on two parameters not relevant to the classical bistatic theorem: The product of the wave number times the characteristic dimension, and the bistatic angle between the incident and scattered wave.
A note on short-range ground characterization
Authors: Attenborough Keith
Published: October 2005

Short-range measurements of the excess attenuation spectrum from a point source can be used to characterize the acoustical properties of the ground surface but they are influenced by turbulence as well as the ground surface. The geometry used for ground characterization should be a compromise between greatest sensitivity to the acoustical properties of the ground surface and avoidance of turbulence effects. Compromise geometries are suggested together with a method of estimating the effective flow resistivity of the ground surface from the frequency of the first maximum in the excess attenuation spectrum. The use of this method is illustrated for a particular grass-covered farmland.
Diffraction by a screen in downwind sound propagation: A parabolic-equation approach
Authors: Salomons Erik M.
Published: October 2005

The parabolic-equation method is used to study sound diffraction by a screen on an absorbing ground. For a homogeneous atmosphere, results are in good agreement with an analytical diffraction theory, showing that the proposed method to include a screen in the parabolic-equation method is accurate. Results are presented for inhomogeneous atmospheres with logarithmic sound-speed profiles, representative of downwind sound propagation. The results show that meteorology has large effects on sound diffraction by a screen at a frequency of 1000 Hz, and small effects at a frequency of 100 Hz.
Detection of unexpected tones in gated and continuous maskers
Authors: Wright Beverly A. , Dai Huanping
Published: October 2005

The effect of gating a wideband masker on the detectability of tones having unexpected frequencies was assessed using a probe-signal method. This method leads the listener to expect a target frequency by presenting the signal most often at that frequency, and measures sensitivity to other unexpected frequencies via occasionally presented probe tones. For 295-ms signals, the probe-signal contours (percent correct as a function of probe frequency) of two of four subjects were considerably broader for a 295-ms masker than for a continuous masker. For 5-ms signals, the probe-signal contours of four of five subjects were quite broad and similar for both gated and continuous maskers. When the probe-signal contours were expressed as the attenuation in decibels of the probes, the resulting ‘‘probe-signal filters’’ were frequently broader than auditory filters measured using notched noise in the same subjects. This suggests that subjects may monitor multiple auditory filters under some conditions in the probe-signal task. Signal threshold tended to be higher for conditions showing wider probe-signal filters, indicating a potential link between changes in signal threshold due to masker gating and the number of frequency channels that are monitored.
Further evidence against an across-frequency mechanism specific to the detection of frequency modulation (FM) incoherence between resolved frequency components
Authors: Carlyon Robert P.
Published: October 2005

Previously, Carlyon [J. Acoust. Soc. Am. 89, 329–340 (1991)] argued that there exists no across-frequency mechanism specific to the detection of frequency modulation (FM) incoherence, defined as a difference in FM phase, between pairs of resolved frequency components. Experiments are described which attempted to reconcile this conclusion with the results of two recent studies. Wilson et al. [J. Acoust. Soc. Am. 88, 1333–1338 (1990)] reported that the detection of FM imposed on a target component was impaired by the presence of an FM ‘‘interfering tone,’’ and that the size of the effect depended on the FM coherence between interferer and target. Experiment 1 replicated their finding but showed, by using low-pass and wideband noise, that its dependence on FM coherence was consistent with the detection of combination tones and of beating between the interferer and target. Cohen and Chen [ J. Acoust. Soc. Am. 92, 766–772 (1992)] reported that the detection threshold for an FM signal was higher when it was masked by two components modulated coherently with it than when the masker and signal modulations were incoherent. Experiment 2 showed that, when the masker consisted of eight components, thresholds were largely determined by the modulation coherence between the signal and the masker component closest to it in frequency. Experiment 3 presented evidence that Cohen and Chen’s findings were influenced by harmonicity between the masker and signal, even in conditions which attempted to control it. Experiment 4 replicated another of Cohen and Chen’s findings, that when the masker modulation was held constant and the signal FM depth varied, some listeners’ thresholds reached a maximum when the masker and signal FM depths were equal. By manipulating the frequency ratio between masker and signal, it was shown that this finding, too, could be attributed to harmonicity between the signal and one of the masker components. Finally, experiment 5 replicated Carlyon’s (1991) findings at a higher sensation level and with a different pattern of modulation than used previously.
Difference limens for formant patterns of vowel sounds
Authors: Hawks John W.
Published: October 2005

Studies of thresholds for discrimination of formant frequency variation in synthetic vowel sounds have been predominantly limited to variations in a single formant. Here, differences limens (DLs) are presented for multiformant variations expressed in measures of ΔF and as distances in the auditory-perceptual space (APS) proposed by J. D. Miller [J. Acoust. Soc. Am. 85, 2114–2134 (1989)]. DLs for four subjects were estimated along 102 synthetic vowel continua representing five patterns of formant variation [(1) single variation in F1; (2) single variation in F2; (3) parallel simultaneous variation in F1 and F2; (4) opposing simultaneous variation in F1 and F2; and parallel simultaneous variation in F1, F2, and F3] and 17 within- or between-category vowel sounds. Minimal uncertainty methodology was employed utilizing an adaptive up–down procedure with a cued, two-interval forced-choice (2IFC) task. The results of this experiment reflect smaller DLs for both single- and multiple-formant changes than have been found in the past and also suggest that discrimination of parallel multiformant variation is significantly better than opposing multiformant or single-formant variation.
Conditioned constant-Q spectra for improved frequency tracking in the presence of interfering signals
Authors: Dorken Erkan , Nawab S. Hamid
Published: October 2005

A technique is presented for improving the performance of a method for estimating the time-varying fundamental frequency of a signal corrupted by interference components. The original method involves the calculation and comparison of frequency-pair ratios in each short-time spectrum of the corrupted signal [M. Piszczalski and B. A. Galler, ‘‘Predicting musical pitch from component frequency ratios,’’ J. Acoust. Soc. Am. 66, 710–720 (1979)]. As the strength of the interference components is increased, the frequency estimates from this method become more unreliable. To obtain improved performance, a procedure based upon principal components analysis is used to enhance the harmonic signal’s spectral components prior to the calculation of frequency-pair ratios. The resulting improvement in fundamental frequency estimation is demonstrated through examples involving music signals.
Intensity discrimination and increment detection at 16 kHz
Authors: Bacon Sid P. , Viemeister Neal F.
Published: October 2005

When presented for several seconds, a very high-frequency tone can decay to inaudibility in subjects with normal hearing. The purpose of the present study was to determine how such a tone behaves once it is inaudible. Intensity difference limens (DLs) at 16 kHz were measured for gated (audible) and continuous (inaudible) pedestals over a range of pedestal sensation levels from about 0–60 dB, and were compared with those obtained in the same two subjects at 1 kHz [N. F. Viemeister and S. P. Bacon, J. Acoust. Soc. Am. 84, 172–178 (1988)]. The results at the two frequencies were remarkably similar, indicating, among other things, that a continuous 16-kHz pedestal—despite being inaudible—behaves as if it were audible. In addition, the results suggest that there is little or no relationship between high-frequency tone decay and intensity DLs. The locus of this long-term adaptation effect is presumably peripheral to the site where binaural interactions occur, and may be at the hair cell or auditory nerve. The intensity DLs are more consistent with a multiplicative model of (long-term) adaptation than with a subtractive model, suggesting that the nature of this adaptation is different from that which characterizes short-term adaptation.
Monotic and dichotic modulation detection interference in practiced and unpracticed subjects
Authors: Bacon Sid P. , Opie Jane M.
Published: October 2005

The threshold for detecting 10-Hz amplitude modulation of a 1-kHz carrier was measured in quiet and in the presence of a 4-kHz masker carrier that was either unmodulated or amplitude modulated at a depth of 1.0 and at rates from 2 to 80 Hz. The signal and masker were presented to the same ear (monotic condition) or to opposite ears (dichotic condition), and the subjects either had no previous experience with psychoacoustic experiments (n=10) or had from 16 to about 70 h of experience with modulation-detection tasks (n=4). There were no significant differences between the two groups of subjects, although there was a significant effect of presentation mode. Thresholds generally were higher in the monotic condition, particularly when the masker rate was similar to the signal rate. According to excitation-pattern analyses, the greater interference in the monotic condition is unlikely due to peripheral interactions.
Reducing informational masking by sound segregation
Authors: Kidd Gerald , Mason Christine R. , Deliwala Phalguni S. , Woods William S. , Colburn H. Steven
Published: October 2005

Informational masking was reduced using three stimulus presentation schemes that were intended to perceptually segregate the signal from the masker. The maskers were sets of sinusoids chosen randomly in frequency and intensity on each stimulus interval or, in some conditions, on every masker burst in a series of bursts within intervals. Masker components were excluded from the frequency region surrounding the 1000-Hz signal to minimize the energetic masking. Masked thresholds as great as 60–70 dB above quiet threshold were observed for some subjects in some conditions. It was shown that this informational masking could be reduced as much as 40 dB by: (1) presenting the masker to both ears and signal to one ear; (2) playing different masker samples sequentially in each interval of every trial; or (3) presenting the signal in alternate bursts of multiple, identical masker samples. For the binaural manipulation, informational masking was reduced because the masker and signal were perceived as originating from different interaural locations. In the latter two manipulations, a difference in the spectral or temporal pattern of the signal and masker provided the detection cue. These effects were interpreted as evidence of the importance of perceptual segregation of sounds in noisy listening environments where signal reception is not limited by energetic masking.
Formant-frequency discrimination for isolated English vowels
Authors: Kewley-Port Diane , Watson Charles S.
Published: October 2005

Thresholds for formant-frequency discrimination were obtained for ten synthetic English vowels patterned after a female talker. To estimate the resolution of the auditory system for these stimuli, thresholds were measured using well-trained subjects under minimal-stimulus- uncertainty procedures. Thresholds were estimated for both increments and decrements in formant frequency for the first and second formants. Reliable measurements of threshold were obtained for most formants tested, the exceptions occurring when a harmonic of the fundamental was aligned with the center frequency of the test formant. In these cases, unusually high thresholds were obtained from some subjects and asymmetrical thresholds were measured for increments versus decrements in formant frequency. Excluding those cases, thresholds for formant frequency, ΔF, are best described as a piecewise-linear function of frequency which is constant at about 14 Hz in the F1 frequency region (<800 Hz), and increases linearly in the F2 region. In the F2 region, the resolution for formant frequency is approximately 1.5%. The present thresholds are similar to previous estimates in the F1 region, but about a factor of three lower than those in the F2 region. Comparisons of these results to those for pure tones and for complex, nonspeech stimuli are discussed.
On sound in an inverse sinusoidal nozzle with low Mach number mean flow
Authors: Campos Luis M. B. C. , Lau Fernando J. P.
Published: October 2005

The quasi-one-dimensional propagation of sound, in a throated convergent–divergent nozzle, with entry and exit baffle at finite distance, containing a low Mach number mean flow, is studied in four steps. The low Mach number nozzle wave equation, is obtained, both for the acoustic potential and velocity, using two methods, viz. (a) elimination between the equations of motion and (b) an acoustic variational principle. For the case of inverse sinusoidal ducts, exact solutions are obtained, in terms of elementary functions, for the acoustic potential and velocity, in horns and nozzles. The reduced acoustic velocity, i.e., correction to ray approximation, is reconsidered as an exact, closed series solution, of a modified Mathieu equation, with imaginary coefficients. The plots of amplitude and phase versus distance, for various low Mach numbers, and increasing wave numbers show a number of effects, which may be interpreted as follows: (i) acoustic energy is focused in the converging duct, leading to a peak half-way between baffle and throat; (ii) a part of the sound field is reflected before the throat, leaving a weaker propagating acoustic field after. Thus although the duct is symmetric relative to the throat, the sound field is unsymmetric, due to the initial one-directional propagation, this effect being most marked for half-wavelength comparable to the length of the duct.
Acoustic calibration of a pressure-velocity probe
Authors: Lazreq Z. , Ville J. M.
Published: October 2005

A probe consisting of a hot-wire and a microphone has been developed and built to measure in flow conditions acoustic pressure and particle velocity as well as mean flow velocity. To calibrate this probe, a new measurement process has been developed to determine the transfer function of each transducer. The theoretical basis and the experimental results are presented in this paper. To validate this new measurement method, theoretical and experimental results of an open-end unflanged duct reflection coefficient are compared. They show as expected that when the measurements on each transducer are corrected by the transfer function, theoretical and experimental results are in good agreement.
Development of the cochlear amplifier
Authors: Mills David M. , Rubel Edwin W.
Published: October 2005

The development of the cochlear amplifier was examined in gerbils aged 14 days after birth (dab) to adult, for stimulus frequencies from 1 to 48 kHz. Distortion product otoacoustic emissions (DPOAEs) were employed to determine the characteristics of active emissions associated with cochlear amplifier operation. DPOAEs were also used to determine the characteristics of ‘‘passive’’ emissions remaining when the cochlear amplifier operation was interrupted by acute furosmide intoxication. The input–output functions of the passive emissions, and of the active emissions at low stimulus levels, could be approximated by parallel straight lines. The horizontal distance between these parallel lines, i.e., the increase in stimulus level required to obtain a passive emission amplitude equal to the active emission, is an estimate of the gain of the cochlear amplifier. Further, the lowest stimulus level at which active and passive emissions become approximately equal defines a passive threshold level. At 14 dab, the cochlear amplifier gain was already at adult levels for the midfrequencies (4–8 kHz), but no emissions were detected at the extremes (at 1 kHz, and 24 kHz and above). During the period over which the endocochlear potential (EP) is known to increase most sharply (14 to 18 dab), the gain at all frequencies increased. At low frequencies there was little or no gain in the youngest age group, but matured by 23 dab. The gain at the middle frequencies subsequently decreased, resulting by 30 dab in a gain that was remarkably flat across frequency from 1 to 32 kHz. The passive thresholds generally improved with age at all frequencies, but most dramatically at the high frequencies. Results are consistent with the view that the elements of the cochlear amplifier are functional in the base of the cochlea at all ages, but that auditory function is primarily limited by the lower passive base cutoff frequency at younger ages. The proposed increase in passive base cutoff frequency with age accounts for the known place code shift.
Effect of loudness recruitment on the perception of amplitude modulation
Authors: Moore Brian C. J. , Wojtczak Magdalena , Vickers Deborah A.
Published: October 2005

People with hearing loss of cochlear origin usually display loudness recruitment; the rate of growth of loudness level with increasing sound level is greater than for a normally hearing person. Loudness recruitment has usually been studied with steady sounds of relatively long duration. The present study examines how recruitment affects the perception of dynamically varying sounds, namely amplitude modulated sinusoids. The modulation rates used (4, 8, 16, and 32 Hz) were chosen to span the range of the most prominent modulations present in the envelope of speech. Three subjects with unilateral cochlear hearing loss were used. In experiment 1, subjects were required to make loudness matches between 1-kHz tones presented alternately to the two ears. This was done over a wide range of sound levels. Experiment 2 used 1-kHz carriers that were amplitude modulated. The modulation was sinusoidal on a dB scale. The modulated tones were presented alternately to the two ears and were approximately equally loud in the two ears. The modulation depth was fixed in one ear, and the subject was required to adjust the modulation depth in the other ear so that the modulation depth appeared equal in the two ears. This was done for a range of modulation depths and with the fixed tone presented to both the normal and the impaired ear. A given modulation depth in the impaired ear was matched by a greater modulation depth in the normal ear. To a first approximation, the modulation-matching functions were independent of modulation rate. Furthermore, the functions could be predicted reasonably well from the loudness-matching results of experiment 1, obtained with steady tones. The results are consistent with the idea that loudness recruitment results from the loss of a fast-acting compressive nonlinearity that operates in the normal peripheral auditory system. Possible implications of the results for the use of fast-acting compression in hearing aids are discussed.
Effect of otoacoustic emissions on just-noticeable differences for intensity in normally hearing subjects
Authors: Probst Rudolf , Harris Frances P.
Published: October 2005

Measurements of spontaneous and click-evoked otoacoustic emissions (OAEs) were used to classify listeners with normal hearing into one of two categories—those with spontaneous emissions (SOAEs) and high-level transiently evoked emissions (TEOAEs) in both ears (strong emissions) and those with no SOAEs and low-level TEOAEs in either ear (weak emissions). Just-noticeable differences (jnd’s) in intensity for 1-kHz pure tones presented at either 60, 40, or 20 dB SL were determined for these two groups using a continuous pedestal technique. Mean jnd’s for intensity for the two groups did not differ significantly. Intratest variability was compared and the group with strong emissions had significantly higher variability for presentation levels of 20 dB SL and lower variability at 60 dB SL. Additional testing of intensity jnd’s was performed in individuals with strong emissions using pure tones 30 Hz lower than a targeted SOAE frequency. Large interindividual differences were present without a specific pattern. It is concluded that OAE activity level does not affect the mean jnd for intensity discrimination. Individuals with strong emissions have less variance when performing the test at higher levels and more variance for lower level stimuli than do individuals with weak emission characteristics. Because an ear’s OAE characteristics can alter performance on psychoacoustic tasks, knowledge of such characteristics is desirable when psychoacoustic results are acquired and reported.
Cochlear hearing loss and the processing of modulation: Effects of temporal asynchrony
Authors: Grose J. H. , Hall J. W.
Published: October 2005

Temporal coincidence and envelope correlation among components of a complex sound are informative cues for the perceptual organization of that sound. Listeners with hearing loss of cochlear origin often exhibit reductions in temporal processing of stimuli with randomly fluctuating envelopes. The purpose of this study was to examine the performance of such listeners on auditory grouping tasks which rely on temporal cues. The first experiment examined temporal asynchrony effects in a comodulation masking release (CMR) task. Performance was poorer than normal and appeared to be associated with reduced frequency selectivity. However, the pattern of asynchrony effects was the same as normal. The second experiment examined temporal asynchrony effects in a task based on envelope comparison interference. On this task, performance was similar to that for normal-hearing listeners. It was concluded that listeners with hearing loss of cochlear origin are comparable to normal-hearing listeners in their ability to make use of relatively gross temporal asynchrony cues.
Perception of the place of articulation of French stop bursts
Authors: Bonneau A. , Djezzar L. , Laprie Y.
Published: October 2005

This paper deals with the perception of French natural stop bursts and with the role played by the following vowel in this perception. The first experiment verified the ability of listeners to identify long stimuli containing the burst and part of the subsequent vowel. The second and third experiments investigated the identification of stop bursts with and without a priori knowledge of the following vowel. In order to determine the discriminating power of spectral characteristics of the burst, these experiments used fixed-length burst stimuli of 25-ms duration with all traces of vocalic segment cut off. The bursts of initial voiceless stops were extracted from CVC isolated words. The burst provided very reliable information about stop place since listeners identified correctly 87% of the stops, without a priori knowledge of the following vowel. Performance however was context-dependent. Knowing the identity of the vowel led to a slight but statistically significant improvement in stop identification. Nevertheless, the effects of this knowledge were selective and varied with context. Finally, the first experiment proved that a near perfect identification of stops can be achieved only when all main cues (burst spectrum, burst duration, and onset of vocalic formant transitions) were present simultaneously.
Acoustic wave scattering from transversely isotropic cylinders
Authors: Honarvar F. , Sinclair A. N.
Published: October 2005

Mathematical expressions are derived for the far-field backscattering amplitude spectrum resulting from oblique insonification of an infinite, transversely isotropic elastic cylinder by a plane acoustic wave. The normal-mode solution is based on decoupling of the scalar potential representing the horizontally polarized shear wave from those of the compressional and vertically polarized waves. The solution degenerates to the well-known simple model for isotropic cylinders in the case of very weak anisotropy. The solution is used to study the influence of each element of the stiffness matrix on the various resonant modes of vibration. Perturbations of the elements c33 and c44, which characterize the cylinder along the axis, significantly affect resonant frequencies corresponding to axially guided waves. Perturbations of c11 and c12, which characterize the material on the transverse plane, predominantly affect the Rayleigh and Whispering Gallery resonance frequencies. Perturbations of c13 affect all three types of resonances. These results are consistent with elasticity theory and the known modal shapes of these resonances.
A three-dimensional finite difference simulation of sonic logging
Authors: Liu Qing-Huo , Schoen Eric , Daube François , Randall Curt , Liu Hsui-lin , Lee Ping
Published: October 2005

A three-dimensional finite-difference (FD) method is used to simulate sonic wave propagation in a borehole with an inhomogeneous solid formation. The second-order FD scheme solves the first-order elastic wave equations with central differencing in both space and time via staggered grids. Liao’s boundary condition is used to reduce artificial reflections from the finite computational domain. In the staggered grids, sources have to be implemented at the discrete center in order to maintain the appropriate symmetry in an axisymmetric borehole environment. The FD scheme is validated for multipole sources in three special media: (i) a homogeneous medium; (ii) a homogeneous formation with a fluid-filled borehole; and (iii) a horizontally layered formation. The staircase approximation of a circular borehole introduces little error in dipole wave fields, although it causes a noticeable phase velocity error in the monopole Stoneley wave. This error has been drastically reduced by using a material averaging scheme and finer grids. Numerical examples show that the FD scheme can accurately model 3-D elastic wave propagation in complex borehole environments.
End resonance in infinite immersed rods of different cross sections
Authors: de Billy M.
Published: October 2005

The edge resonance was discovered by E. A. G. Shaw [J. Acoust. Soc. Am. 28, 38–50 (1956)]. Since that time, many theoretical investigations justified this unusual behavior observed at the end of a free semi-infinite plate by the superposition of the incident and three reflected waves. In the present study, a spectrum analysis technique is used to investigate the frequency response of a short acoustic pulse, normally incident on the end of infinite loaded steel rods of circular and noncircular (square, hexagonal, and rectangular) cross sections. For such samples, the experimental data confirm the existence of end resonances. The results give rise to a resonance frequency dependence with the cross-sectional area which does not depend on the shape of the cross section but only on the value of the area. Particular attention is devoted to the rectangular-section rod, intermediate sample between the one-dimensional problem (semi-infinite plate) and the two-dimensional problem (square rod).
A boundary integral formulation for two-dimensional acoustic radiation in a subsonic uniform flow
Authors: de Lacerda L. A. , Wrobel L. C. , Mansur W. J.
Published: October 2005

This paper presents a new boundary integral formulation for two-dimensional acoustic radiation in a uniform subsonic flow in which the Green’s function automatically incorporates the convective effect. The integral equation representation is derived in detail, and shown to incorporate the Sommerfeld radiation condition at infinity. The order of singularities in the integrals is also analyzed. The resulting integral equation involves the derivative of the velocity potential in the flow direction; thus an approximation is necessary to express this extra variable in terms of the potential and its normal derivative. Numerical results are included to verify the formulation.
Pitch of iterated rippled noise
Authors: Yost William A.
Published: October 2005

Iterated rippled noise (IRN) stimuli are generated by a cascade of delay (d), gain (g), and add networks. The matched pitch of IRN stimuli was determined as a function of the type of network used to generate IRN stimuli, the delay (d=2, 4, and 8 ms), the number of iterations (n=1,2,3,4,6,8) of the delay and add networks, and whether the delayed noise was added (g=1) to or subtracted (g=−1) from the undelayed noise. The matched pitch of IRN stimuli did not depend on the type of network. When g=1 (addition), the matched pitch did not depend on the number of stages of iterations (n) and was always equal to the reciprocal of the delay (1/d). When g=−1 (subtraction), the match pitch depended on n. When n=1, the matched pitch of IRN stimuli was ambiguous having two pitches in the region of 1/d±10%. When n=8, the match pitch was equal to 1/2d. This change in the pitch occurred between n=2 and 6. The results are discussed in terms of spectral and temporal models of complex pitch processing. A temporal model based on autocorrelation was able to provide quantitative predictions for the pitch of these IRN stimuli. However, a spectral type of model can also account for the pitch of these IRN stimuli.
Tutorial on sound propagation outdoors
Authors: Embleton Tony F. W.
Published: October 2005

Concerns about noise in the community date back to the dawn of recorded history. Then, after centuries of relatively little activity, scientific interest grew during the 17th century and social concerns were again voiced during the 19th century. Many of the wave-propagation mechanisms relevant outdoors were understood at least qualitatively by the late 1800s. Today, knowledge of sound propagation phenomena is of great economic and social importance because of environmental and other concerns. Reality is more complicated than geometrical spreading above flat ground. Some grounds are acoustically hard like concrete, and others soft as snow. Corresponding reflection coefficients are complex and vary with angle. Grounds may not be flat, leading to shadow zones or alternatively multiple reflections at the ground. Gradients of wind or temperature refract waves either upwards (upwind or in a temperature lapse) or downwards (downwind or in a temperature inversion). Atmospheric turbulence causes fluctuations in the acoustical effects. Many of these features mutually interact. Measured sound pressure levels owe as much to near-surface weather and to ground shape and impedance as to acoustical factors such as source and receiver heights and their separation. This tutorial paper emphasizes field measurements and simple physical interpretations.
Vibration and sound radiation of fluid-loaded stiffened plates with consideration of in-plane deformation
Authors: Berry A. , Locqueteau C.
Published: October 2005

A Ritz method is presented for computing the vibration and sound radiation of baffled rectangular plates reinforced by eccentric stiffeners. The model incorporates both bending, transverse shear and in-plane deformation of the plate, and bending, torsional, and extensional deformation of the stiffeners. The in-plane deformation of the plate, resulting from the eccentric stiffener deformations, has not been considered in previous studies. Relevant expressions of the kinetic and strain energies of the mechanical system are detailed. Numerical results of the in-vacuo natural frequencies for various configurations of plate thickness, stiffeners, and boundary conditions show the importance of in-plane displacements of the plate, especially when thick plates are involved. The comparisons in terms of in-vacuo natural frequencies between the present approach and available published results as well as FEM calculations show a good agreement. An example of structural response and sound radiation in water is also presented.
Spectral statistics in damped systems. Part I. Modal decay rate statistics
Authors: Burkhardt John , Weaver Richard L.
Published: October 2005

A revised model for the statistical distribution of eigenmode decay rates in complex acoustic systems is presented. Analytical predictions based on a real-valued diffuse field description of modal amplitudes indicate that modal decay rates should be distributed according to a modified chi-square distribution. Numerical experiments performed on damped, irregularly shaped membranes indicate that the chi-square distribution is accurate, provided the membrane is sufficiently lightly damped. For high dissipation levels, as measured by the mean modal overlap, the observed decay rates increasingly disagree with the prediction.
Spectral statistics in damped systems. Part II. Spectral density fluctuations
Authors: Burkhardt John , Weaver Richard L.
Published: October 2005

The effect of dissipation on the fluctuations of the natural frequency spectra of complex systems is studied. Specifically the correlations observed in numerically calculated, damped, natural frequency spectra are compared with the correlation predictions of the Gaussian orthogonal ensemble (GOE) of random matrix theory. It is found that damped natural frequency spectra posses intermodal correlations in accordance with the predictions of the GOE provided damping is moderate. As dissipation levels rise, as measured by the system’s reverberance, it is indicated that the correspondence between the predictions of the GOE and observed fluctuations weakens. The results of a theoretical perturbation analysis are presented which support the observed trends.
A cross-language comparison of vowel perception in English-learning and German-learning infants
Authors: Polka Linda , Bohn Ocke-Schwen
Published: October 2005

Studies of cross-language consonant discrimination have shown a shift from a language-general to a language-specific pattern during the first year of life. Recently, the same pattern of change was observed for English-speaking infants’ discrimination of two non-native vowel contrasts (Polka and Werker, 1994). The present study was designed to provide a more direct assessment of language-specific influences on infant vowel contrast perception. In experiment 1 adults were tested on a German (non-English) contrast, /dut/ versus /dyt/, and an English (non-German) contrast, /dεt/ versus /dæt/. English and German adults discriminated both contrasts with high levels of accuracy in a categorial AXB task. However, results of an identification and rating task showed that, within each non-native vowel contrast, one vowel perceptually matched a native vowel category better than the other. In experiment 2 discrimination of /dut/ versus /dyt/ and /dεt/ versus /dæt/ was examined in English- and German-learning infants in two age groups (6–8 months and 10–12 months) using the conditioned headturn procedure. English and German infants did not differ in their discrimination of either contrast and there were no age differences in discrimination of either contrast for the German or for the English infants. However, in both language groups at both ages, there were clear differences in performance related to the direction in which the vowel change was presented to the infants. For the German contrast, discrimination was significantly poorer when the contrast changed from /dut/ to /dyt/. For the English contrast, discrimination was significantly poorer when the contrast changed from /dæt/ to /dεt/. The directional asymmetries observed here and in other infant vowel studies point to a language-universal perceptual pattern which suggests that vowels produced with extreme articulatory postures serve as perceptual attractors in infant vowel perception.
Elastic wave contributions in high-resolution acoustic images of fluid-filled, finite cylindrical shells in water
Authors: Kaduchak Gregory , Wassmuth Chad M. , Loeffler Charles M.
Published: October 2005

Recent studies of plane wave scattering by finite, evacuated cylindrical shells at oblique incidence describe monostatic echo contributions from surface elastic waves. These waves follow helical paths along the shell’s surface and are guided back in the source direction after reflection from the cylinder truncation. The present research examines similar effects viewed in the time signature of a high-resolution acoustic imaging system. The experimental technique utilizes a narrow beam consisting of a short tone burst to probe a cylindrical shell along its axis of symmetry. The echo returns contain information which yields insight into local scattering processes at the impedance discontinuities of the finite scatterer. The cylindrical shell has a thickness-to-radius ratio h/a=5.5%. It is immersed in water and is subject to both exterior and interior fluid loading. Prominent artifacts are shown to coincide with near axial coincidence of the s0 and a0 Lamb waves. The echo contributions are extremely sensitive to the angle of incidence and interior fluid loading. By placing small ‘‘cuts’’ along the cylinder, it is possible to mimic the truncation effects for different scattering processes.
The acoustical properties of fluid in a wall-driven elastic tube
Authors: Harley T. R.
Published: October 2005

The acoustics of a fluid in a long cylindrical tube is analyzed. The tube’s wall is thin, elastic, and externally driven by a phased array of ring-shaped piezoelectric ceramic transducers. The rings influence the radial motion of the tube’s wall. Applications of the theory to an active wall impedance tube and a toroidal tube are considered. In the toroidal tube, a digitally controlled electronic system drives the transducer array with a fixed wave number and a continuously variable frequency. If the tube wall were rigid, the fluid pressure reaches a resonant maximum when the wave number and frequency of the driven transducer array matches that allowed by the dispersion relation of sound in the homogeneous fluid. Experimentally determining the fluid’s homogeneous sound speed is more difficult, however, when the wall is not rigid. The idea of using the tube’s external airborne sound to noninvasively measure a fluid’s sound speed is introduced. The theory predicts a minimum in the external sound. At this minimum, the wall is effectively rigid and the transducer array’s phase velocity equals the homogeneous fluid’s phase velocity. Preliminary experimental efforts to make an elastic wall rigid are briefly described.
Analytical study of a disk-type torsional shear-wave radiator immersed in an elastic medium
Authors: Ma Yushieh
Published: October 2005

Based on the previous design of a low-frequency, torsional shear-wave transducer [A. K. Walden and T. R. Howarth, J. Acoust. Soc. Am. 91, 2463(A) (1992)], an analytical model is proposed to predict its acoustic responses. The torsional radiation impedance as well as the propagation of the displacement field, produced by an SH-wave source of this type, in an elastic medium are investigated using proper boundary conditions. Computed results of the torsional radiation impedance and the radiation patterns are presented for a disk-type transducer placed in an elastic medium that may have various shear stress distributions at the contact plane. Radiated displacements in the near and far field of the transducer are studied in detail. Acoustic responses reveal that the use of SH-wave energy for an in-depth shear wave exploration is quite possible. These results are also useful for the design of an optimal shear-wave transducer in ocean geoacoustics as well as in an increasing number of other applications using shear-wave energy.
Three-dimensional acoustic scattering of a source-generated field from a cylindrical island
Authors: Athanassoulis Gerassimos A. , Prospathopoulos Aristides M.
Published: October 2005

In this work, an analytic solution is presented for the three-dimensional (3-D) problem of acoustic scattering from a nonpenetrable cylindrical island in shallow water. The ocean environment around the island is considered range independent, with arbitrary sound-speed profile, and the bottom is assumed to be rigid. The total acoustic field generated by an harmonic point source is obtained as a normal-mode, double-series expansion. A systematic numerical investigation of the double series is presented. Results concerning the pressure field and the transmission loss around the cylindrical island are given for the case of an acoustically soft and an acoustically hard island boundary in an isovelocity environment. The presented analytic solution is numerically efficient for relatively low frequencies, and can serve as a 3-D benchmark solution in the appropriate frequency range.
Surface waves in three-dimensional half-space tetragonal solids
Authors: Tewary V. K. , Fortunko C. M.
Published: October 2005

The delta-function representation of the elastodynamic Green’s function is applied to calculate the three-dimensional waveforms for elastic-pulse propagation at the free surface in a half-space tetragonal solid.
Lattice correction to mechanical admittance of solids
Authors: Tewary V. K. , Fortunko C. M.
Published: October 2005

The singularity in the imaginary part of the point mechanical admittance of a solid, as predicted by the continuum model, can be removed by taking into account the discrete structure of the lattice. As an example, a new nonsingular expression for the point mechanical admittance of a solid is derived for scalar waves by using the Debye model Green’s function, which incorporates the lattice effects by restricting the wave vector to the first Brillouin zone of the solid.
Time evolution of acoustic streaming from a planar ultrasound source
Authors: Kamakura Tomoo , Sudo Takehito , Matsuda Kazuhisa , Kumamoto Yoshiro
Published: October 2005

Eckart-type acoustic streaming induced in confined sound beams from a piston source is examined in water theoretically and experimentally. Axisymmetric flow equations with a spatially distributed driving force in the beams are based on the continuity equation and the Navier–Stokes equation in a viscous, incompressible fluid. They are solved numerically by the stream-function vorticity method [T. Kamakura et al., J. Acoust. Soc. Am. 97, 2740–2746 (1995)]. Experiments are conducted using a 5-MHz planar transducer with a 9.5-mm radius aperture. All measurements of the streaming velocities are carried out by a laser Doppler velocimeter and are compared with the numerical computations including the enhancement of the force due to finite-amplitude sound distortion. These measurements agree well with the theoretical prediction. It is noted that diffraction of sound beams plays an important role in the generation of streaming, particularly in the early stage. Consistency between experiments and computations suggests that both acoustic and hydrodynamic nonlinearities should be taken into account in the present observation system.
Solitons, pulse splitting, and AM–FM conversion in cylindrical ducts
Authors: Larraza Andrés , Coleman William F.
Published: October 2005

For propagation above cutoff in an acoustic duct, the dispersion is positive and weakly nonlinear effects are of two kinds. When the wavelength decreases with amplitude, a localized envelope propagates without spreading or distortion and the resultant final state is a soliton. Sloshing modes in a cylindrical duct of finite eccentricity belong to this class. When the wavelength increases with amplitude, a localized envelope splits into two disturbances moving with two different velocities of propagation. As a consequence, if a signal is amplitude modulated at the source, spatial beating between the two disturbances will occur, and at periodic positions in space the signal will become frequency modulated. Axially symmetric cross modes in a cylindrical duct of circular cross section belong to this class. A quantitative analysis of the results of the theory is presented along with its experimental consequences.
Numerical prediction of sound transmission through finite multilayer systems with poroelastic materials
Authors: Panneton Raymond , Atalla Noureddine
Published: October 2005

The sound transmission performance of finite multilayer systems containing poroelastic materials is of utmost importance for noise control in automobiles, aircrafts, buildings, and several other engineering applications. Currently, the need for tools predicting the acoustical and structural behaviors of such structures is considerably increasing. In this paper, such a tool is presented. It is applied to the sound transmission loss through multilayer structures made from a combination of elastic, air, and poroelastic materials. The presented approach is based on a three-dimensional finite element model. It uses classical elastic and fluid elements to model the elastic and fluid media. For the poroelastic material, it uses a two-field displacement formulation derived from the Biot theory. Furthermore, it couples with a boundary element approach to account, when important, for fluid–structure coupling and to calculate the transmission loss through the multilayer structure. Numerical predictions of the transmission loss through a poroelastic material sandwiched between two finite elastic plates are presented for various configurations. It is shown that the unbonded/bonded configuration gives better transmission loss. Also, comparisons with laterally infinite double panels and with an equivalent fluid approach for the porous material are presented. It is shown that these two simplified models lead to erroneous predictions at low frequencies and for certain design configurations, respectively.