bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of phase distortion in the synthesis of head-related transfer functions
Authors: Blommer Michael A. , Wakefield Gregory H.
Published: October 2005

Synthesizing over headphones the free-field to ear-canal transfer functions, or head-related transfer functions (HRTFs), of the human auditory system poses several difficulties from the standpoint of digital signal processing. Since the order of the HRTF is unknown, it is necessary to assume a particular value when estimating the HRTF from responses obtained in an anechoic chamber. Additionally, while standard filter designs minimize the squared error between the desired and designed response, applications such as HRTF synthesis are likely to require error metrics that are sensitive to disparities between the log magnitude response of each system. A new design algorithm is proposed that is based on a logarithmic distortion metric and it is shown how this algorithm can be used to obtain minimum phase, low-order pole-zero approximations to HRTFs. Psychophysical results characterizing audibility sensitivity to such HRTF approximation errors are presented in order to establish an audible limit for the distortion in such designs. These results are compared with similar experimental results for the widely used least-squares metric. [Research supported by a grant from the NIDCD of the National Institute of Health.]
Rate of loudness growth for pure tones in normal and impaired hearing
Authors: Hellman Rhona P. , Meiselman Carol H.
Published: October 2005

The present article provides an analysis of loudness growth rates in normal and cochlear-impaired hearing for diverse groups with respect to age and backgrounds. Slopes are obtained from absolute magnitude estimation and magnitude production of loudness (measured values), and from cross-modality matching and absolute magnitude estimation of apparent length (predicted values). Consistent with an earlier study [R. P. Hellman and C. H. Meiselman, J. Acoust Soc. Am. 88, 2596–2606 (1990)], slopes calculated within the 15–30 dB stimulus range above the elevated threshold increase in size with the degree of hearing loss. The corresponding range of loudness values in normal hearing yields a slope near 0.60 independent of the threshold levels. This pattern of loudness growth holds for individuals and groups. But the intersubject variability of the slope is more labile, being larger across than within groups and larger for the measured slopes than for the predicted values. Determined from the predicted slopes, the coefficient of variation, σ/m, is approximately constant in normal and impaired hearing ranging from 20%–27%. In contrast, σ/m, obtained from the measured slopes, increases with the degree of hearing loss to a value of almost 50% for a 75-dB loss. The overall stability and systematics of the observed effects further demonstrate that the loudness–intensity relation can be specified with reasonable precision and accuracy from cross-modality matching.
Complex noise exposures: An energy analysis
Authors: Ahroon William A. , Hamernik Roger P. , Davis Robert I.
Published: October 2005

Industrial noise environments usually present a complex stimulus to the exposed individual. These environments often contain mixtures of multiply reflected impact noises and a relatively Gaussian broadband noise. Noise exposure standards do not consider the possibility of interactions between the two classes of noise that can exacerbate the amount of hearing trauma. This paper presents the results of a large series of experiments designed to document the hazard posed to hearing from complex noise exposures. Twenty-three groups of chinchillas with 5 to 11 animals per group (total N=135) were exposed for 5 days to either octave bands of noise, impacts alone, or combinations of impact and octave bands of noise. Evoked potential measures of hearing thresholds and cochleograms were used to quantify the noise-induced trauma. The results show that, for sound exposure levels (SEL) which produce less than approximately 10 dB PTS (permanent threshold shift) or 5% total sensory cell loss, equal-energy exposures tend to produce equivalent effects on hearing. However, there is a range of at least 10 dB in the SEL parameter where hearing loss from equal-energy exposures at a particular SEL can be exacerbated by increasing the repetition rate of the impacts or by the addition of a Gaussian low-level noise. The exacerbation of trauma from the addition of a Gaussian continuous noise is dependent upon the spectrum of that noise.
Transient axial solution for the reflection of a spherical wave from a concave ellipsoidal mirror
Authors: Hamilton Mark F.
Published: October 2005

A transient solution is derived for the reflected pressure along the axis of symmetry of a concave ellipsoidal mirror. The incident field is a spherical wave produced at the near focus of the mirror. It is assumed that the characteristic wavelengths are short in comparison with the minimum radius of curvature of the mirror, that the fluid is lossless and homogeneous, and that small signal theory applies. The reflected pressure is described at the far focus by a simple analytical solution and elsewhere on axis by a convolution integral. The results extend the theory developed for spherical mirrors by Cornet and Blackstock [J. Acoust. Soc. Am. 52, 115 (A) (1972)]. Application of the present theory to waveforms produced by spark-source lithotripters is discussed, and comparisons are made with measurements reported by Müller [Biomed. Tech. 35, 250–262 (1990)].
Performance of various shapes of hydrophones in the reduction of turbulent flow noise
Authors: Ko Sung H.
Published: October 2005

Turbulent boundary layer pressure fluctuations can be reduced by filtering of its wave-number response with either a finite hydrophone or a hydrophone array, or by filtering the wave-number response through an elastomer layer. In general practice, various configurations of hydrophone arrays are embedded within a layer of elastomer, thus reducing the turbulent boundary layer pressure fluctuations. The theoretical model considered in this paper is a plane elastomer layer backed by an infinitely rigid surface; the front side of the layer is exposed to turbulent flow. This paper examines the performance of various shapes (square/rectangle, triangle, rhomboid, and circle) of hydrophones flush-mounted on a rigid surface and embedded within the elastomer layer in reducing the turbulent flow noise. The results presented are numerically calculated noise reductions for various parameters related to hydrophone shapes.
Analysis of reflection characteristics of a normal incidence plane wave on resonant sound absorbers: A finite element approach
Authors: Easwaran V. , Munjal M. L.
Published: October 2005

Resonant sound absorbers are used widely as anechoic coatings in underwater applications. In this paper a finite element scheme based on the Galerkin technique is used to analyze the reflection characteristics of the resonant absorber when insonified by a normal incidence plane wave. A waveguide theory coupled with an impedance matching condition in the fluid is used to model the problem. It is shown in this paper that the fluid medium encompassing the absorber can be modeled as an elastic medium with equivalent Lamé constants. Quarter symmetry conditions within the periodic unit cell are exploited. The finite element results are compared with analytical results, and with results published elsewhere in the literature. It is shown in the process that meshing of the fluid domain can be obviated if the transmission coefficients or reflection coefficients only are desired as is often the case. Finally, some design curves for thin resonant absorbers with water closure are presented in this paper.
Low-frequency oscillations of bubble plumes
Authors: Koller D. P. , Shankar P. M.
Published: October 2005

A simple model is proposed to explain the generation of low-frequency oscillations of bubble plumes. The bubbly medium surrounded by water is considered as a waveguide {cylindrical plume [N. Q. Lu et al., IEEE J. Ocean. Eng. 15, 275–281 (1990)]}, with Bessel functions [Jm(⋅)] representing the oscillatory nature of the acoustic field inside the plume while modified Bessel functions [Km(⋅)] represent the evanescent field in the bubble-free water. The resonant frequencies of the plume have been calculated as a function of the void fraction. There is reasonable agreement between theoretically calculated frequencies and the experimentally observed acoustic signals.
A matched-mode processing technique for localizing a transient source in the time domain
Authors: Lu I-Tai , Chen Han-Yang , Voltz Peter
Published: October 2005

A matched-mode processing method separates the range and depth estimation tasks, thereby obtaining a sequential procedure that circumvents the need for a two-dimensional search over all hypothesized source locations. Therefore, when applicable, it is more efficient than a matched-field method. Here, the conventional frequency-domain, matched-mode method is extended to deal with more realistic nonharmonic, narrow-band signals directly in the time domain. The modes are separated by the conventional modal filtering approach. Then, the source range and depth information can be estimated by the relative arrival times and energies of a relatively well-behaved subset of the modal arrivals. In this way, the problem of modal phase ambiguity is removed, and the entire frequency content of the modal arrivals is coherently combined by operating directly on the time waveforms. Moreover, this approach does not require a prior knowledge of the source waveform. In the numerical simulation, the source and receiver arrangement and the ocean parameters are taken from an experimental setup in the Mediterranean Sea [S. M. Jesus, J. Acoust. Soc. Am. 90, 2034–2041 (1991)].
Acoustic signature of dispersive and orthotropic composites using a focused microscope
Authors: Deschamps M. , Som A.
Published: October 2005

This paper presents a theoretical investigation of the reflection of focused acoustic beams from a viscoelastic orthotropic composite. The reflection coefficients taking the anisotropy of the composite into account are expressed in terms of nine complex elastic constants. Using a classical Fourier optical method, the reflected beams by an anisotropic and absorbing medium are obtained theoretically for various defocus positions of the lens and for different line focus directions. In agreement with the Snell’s laws, any waves generated in the specimen are bulk heterogeneous plane waves. In addition, for a unidirectional carbon fiber/epoxy matrix composite the oscillations due to the generation of lateral wave in the medium are compared with the critical angle associated with these waves at various azimuthal angles. Conclusions are drawn regarding the use of focused beams in the inverse problem to recover elastic constants of composite materials.
Excitation of a fluid-filled, submerged spherical shell by a transient acoustic wave
Authors: Zhang Peizhen , Geers Thomas L.
Published: October 2005

A mathematical formulation and method of solution for the title problem are developed, and numerical results are presented for excitation by a plane step wave. The formulation is based on the familiar equations of motion for a thin spherical shell and the wave equation for the internal and external fluid domains. The Laplace transform is invoked, and the usual separation of variables method produces modal equations for each component of the Fourier–Legendre series solution. The modal equations are then restructured to facilitate transform inversion, yielding delayed differential equations in time for each response mode of the shell-fluid system, which are integrated numerically in time. Complete response solutions then follow by modal superposition, with special techniques being employed to improve modal convergence. Transient response histories are shown for a step-wave-excited steel shell containing water and submerged in water. Also, these results are compared with their counterparts for an empty submerged steel shell.
An exact Laplace transform formulation for a point source above a ground surface
Authors: Di Xiao , Gilbert Kenneth E.
Published: October 2005

An exact analysis is given for a point source in air above a ground surface. By representing the plane-wave reflection coefficient as the Laplace transform of an image source distribution, a well-behaved image integral, instead of the usual Sommerfeld integral, is obtained. The approach is valid for both locally and extended reacting surfaces. For a locally reacting ground surface, the image integral is an especially simple, rapidly convergent integral. The integral for local reaction is investigated analytically for a number of limiting cases. The resulting analytic solutions are compared with analytic solutions obtained from more standard approaches. Finally, the image integral for local reaction is analyzed numerically, and an upper limit on the numerical integration is given. It is shown that with realistic values of ground impedance, the prescribed integration limit allows the image integral to be easily and accurately computed numerically.
Determination of compressional wave and shear wave speed profiles in sea ice by crosshole tomography—Theory and experiment
Authors: Rajan Subramaniam D. , Frisk George V. , Doutt James A. , Sellers Cynthia J.
Published: October 2005

Sea ice is a heterogeneous material whose acoustic properties are functions of time and space. Results of a crosshole tomography experiment conducted in multi-year ice with the objective of determining the spatial structure of the compressional and shear wave speeds from travel time measurements made with high-frequency pulses are presented here. The results of the experiment indicate that the wave speeds can be determined from such a crosshole experiment with good resolution. The compressional and shear wave speed contour maps indicate that the spatial variations of the wave speeds are complex with regions of low speed. Low-speed regions observed are likely caused by high brine volume content. Resolution and variance studies performed on the estimates are also presented. Material properties such as Poisson’s ratio, salinity, and elastic and shear moduli of sea ice are obtained from the estimates of compressional and shear wave speeds. By measuring the amplitude of the transmitted and received signals along specific paths, estimates of the attenuation coefficients at different depth intervals are obtained. Spatial variability observed in the estimates is believed to be due to scattering by inhomogeneities in the material.
Modeling ambient noise in three-dimensional ocean environments
Authors: Perkins John S. , Kuperman W. A. , Ingenito F. , Fialkowski Laurie T. , Glattetre John
Published: October 2005

A model is developed for the calculation of the spatial properties of the surface-generated noise in a three-dimensional ocean. This is an extension of the work of Kuperman and Ingenito [J. Acoust. Soc. Am. 67, 1988–1996 (1980)], which used a normal-mode representation of the noise field in a stratified ocean. Noise fields are simulated for both point receivers and vertical line receivers. These examples show how the spatial and directional characteristics of the noise field are affected by the ocean environment. For example, as is apparent in ambient noise data, surface noise propagating at high angles over a sloping ocean bottom is deflected into shallower angles. Also, matched-field processing simulations in three-dimensional ocean environments can be done in a consistent manner: signals and surface-generated noise are modeled by propagating through the same environment with the same theory.
Acoustical properties of interacting particles
Authors: Al-Nimr M. A. , Arpaci V. S.
Published: October 2005

Acoustical cross sections of random homogeneous dense systems of interacting Rayleigh particles are studied analytically. A model for the radial distribution function is proposed. The role of the far-field and the near-field effects on the acoustic characteristics is investigated. It is found that the near-field effect on the scattered sound is negligible compared to the far-field effect. The validity of some assumptions is investigated. It is found that interaction among particles may increase or decrease the attenuation effect depending on the volume fraction and the properties of the particulate system.
Complex wave-number decomposition of structural vibrations
Authors: Grosh Karl , Williams Earl G.
Published: October 2005

A high-resolution parameter estimation technique is used to analyze the spatial dependence of the steady-state vibrations of finite structures. The complex wave-number dependence is extracted using a modified version of the Prony method along with model order overdetermination. This Prony technique forms the basis of an automated algorithm for the robust and efficient estimation of the structural system parameters. A specific algorithm is described and implemented using a wave viewpoint of the spatial response. The algorithm is used to deconvolve the helical wave spectrum of a point driven cylindrical shell from analytic response data. The effects of added noise are studied.
Effects of structural joints on sound scattering
Authors: Guo Y. P.
Published: October 2005

This paper addresses the effects of conditions at attachment points of coupled elastic structures on sound scattering. This is done by examining the scattering of plane sound waves by an infinite elastic plate loaded with fluid on one side and a semi-infinite plate on the other side. Different attachment conditions between the two plates are considered, ranging from clamped connections that transmit both forces and moments to various pinned connections, each of which allows free motions in one or two dimensions at the attachment point. It is shown that in the low- and intermediate-frequency domain, attachments supporting normal forces to the fluid-loaded plate cause much more acoustic scattering than those that only transmit tangential forces and bending moments. The ratio of contributions to the scattered acoustic field, respectively from bending moments and normal forces, is found to be proportional to a (13/5)th power of the plate Mach number, defined by the square root of frequency normalized by the plate coincidence frequency.
Evaluation of dynamic characteristics of an electromagnetic ultrasonic transducer
Authors: Ma Weimin , Sato Takuso
Published: October 2005

An electromagnetic transducer has been used as a high power stress wave source in nondestructive testings and a detailed analysis of its dynamic characteristics is desired to construct more precise measuring systems. In this paper, first the magnetic field generated by a ring symmetric current on an infinite metal surface with a given waveform is derived. Then, the closed-form solution of the electromagnetic force per unit volume in metal generated by a zero sectional ring coil is given. As a limiting case, when the conductivity of the metal is infinite, the electromagnetic force can be expressed as the product of time and radial coordinate functions. The characteristics of electromagnetic force per unit volume in metal generated by the zero sectional ring coil are evaluated as the function of conductivity of the metal and the distance between the coil and the surface of metal. It is also shown that Eisenmenger’s [Acustica 12, 185–202 (1962)] treatment is a special case of this formulation when the distance between the coil and the surface of the metal is infinitesimally small and the conductivity of metal is infinite. Finally, the transient characteristics of a stress perturbation wave in metal are also evaluated.
Wave propagation in a pyroelectric cylinder of arbitrary cross section with a circular cylindrical cavity
Authors: Paul H. S. , Raman Ganapathy V.
Published: October 2005

Flexural and longitudinal vibrations in an arbitrary shaped pyroelectric infinite cylinder of crystal class 6 with circular cylindrical cavity is considered. The inner and outer surfaces of the cylinder are traction free, earth connected, and thermally insulated. The boundary conditions are satisfied directly at the regular inner surface and the Fourier series collocation method is applied at the outer boundary to satisfy the boundary conditions. A frequency equation has been derived for crystal class 6 for a general cross section. The frequency equation is analyzed numerically for elliptical and cardioidal cross-section cylinders of crystal class 6mm since all the material constants for class 6 are not available. Barium titanate ceramic is taken for numerical calculations. The results are tabulated and are presented graphically.
Comments on ‘‘Diffraction constants of acoustic transducers’’ [J. Acoust. Soc. Am. 3
6, 267–269 (1964)]
Authors: Milos̆ić Zvonimir
Published: October 2005

The functional dependence of diffraction constants of ‘‘ka’’ for a ring, a sphere, a cylinder, and a piston is correctly presented. The known analytical expressions are used in order to write the software for the graphical presentation.
Monaural phase effects on timbre of two-tone signals
Authors: Ozawa Kenji , Suzuki Yoiti , Sone Toshio
Published: October 2005

The effects of the phase difference between components of a two-tone signal whose components have a frequency ratio of f2/f1=2.0 on its timbre were investigated. In the experiments, the similarities among six signals were judged with the complete method of triads. The subjective space in which the configuration of points with the different phase conditions lay was derived from the data by means of Torgerson’s multidimensional scaling program. An early study stated that the subjective space was a circle. Present results, however, revealed that the subjective space becomes one-dimensional when either the amplitude ratio between components was large or when the frequency of the signal was high. This one-dimensional configuration is interpreted in terms of the partially masked loudness of the higher frequency component of the signal.
Discriminability of narrow-band sounds in the absence of level cues
Authors: Kidd Gerald , Uchanski Rosalie M. , Mason Christine R. , Deliwala Phalguni S.
Published: October 2005

Several experiments are described in which the task of the observer was to detect an intensity increment to the center tone of a narrow-band, multitone complex. The sound-pressure levels of the stimuli were equated, then randomized, so that listeners could not detect the signal by using level cues. The primary experimental variables were the number of tones in the masker spectrum, the level of the center tone or ‘‘pedestal’’ relative to the other tones, the center frequency and the sound-pressure level. Both ‘‘random-phase’’ and ‘‘fixed-phase’’ conditions (referring to whether the pattern of starting phases of the nonsignal tones was chosen randomly on every presentation or was held constant throughout each trial and block of trials) were tested. Although no simple detection strategy appeared to account for all of the results, the most plausible explanation for performance in most conditions was that the listeners were able to discriminate between sounds based on subtle differences in the amplitude envelopes of the waveforms.
Detecting temporal onset and offset asynchrony in multicomponent complexes
Authors: Zera Jan , Green David M.
Published: October 2005

The ability of listeners to detect asynchrony in either the temporal onset or offset of components in multicomponent complexes was measured. The listener discriminated a standard complex, one in which all components were synchronous, from an asynchronous complex. In the initial experiments, asynchrony was created by starting (onset experiments) or ending (offset experiments) the harmonics at times drawn from a Gaussian distribution. In later experiments, asynchrony was created by starting or terminating only certain components before or after the other components in the complex. One complex consisted of 20 harmonic components with a fundamental of 200 Hz. Another multicomponent complex used components spaced at equal intervals in logarithmic frequency (200 to 4000 Hz). The parameters investigated were rise or decay time of components, duration of a complex, and frequency position of displaced components. The obtained thresholds were different for onset and offset asynchrony. For onset asynchrony in harmonic complexes, the thresholds were a nonmonotonic function of rise time with a minimum of 0.2 ms obtained for a rise time of 1 ms. For offset asynchrony, thresholds were generally monotonic with increases in decay time and ranged from 0.45–1.3 ms. Experiments with a much shorter signal duration demonstrated that forward and backward masking played little role in the observed differences in thresholds. Onset thresholds for harmonic stimuli measured as a function of the frequency region of the asynchronous component(s) showed a minimum of 0.2 ms at about 2000 Hz. The thresholds for offset were about ten times larger. For logarithmic complexes, in some conditions, thresholds were larger by nearly two orders of magnitude. Experiments in which the listeners discriminated changes either in the onset or offset envelope of the wideband stimulus suggest that detection of temporal asynchrony depends on comparison between frequency channels rather than on differences in the temporal onset or offset of the overall energy of the sounds.
The performance of adaptive noise cancellation systems in reverberant rooms
Authors: Lu Mean-Hoa , Clarkson Peter M.
Published: October 2005

The performance of adaptive noise cancellation (ANC) systems in a reverberant room is investigated. Room reverberation effects are modeled through the method of images, incorporating both direct signal and reverberation effects into the room impulse response. The performance of ANC for broadband inputs is examined as a function of reverberation time, noise source location, and the geometry of the room and measurement equipment. Expressions are obtained relating the steady-state minimum mean-squared error and excess mean-squared error to the reverberation time and filter parameters. Nonuniform convergence effects are also investigated and bounds on the eigenvalue disparity are obtained for a given configuration. It is shown that the eigenvalue disparity increases as both the filter length and the distance between noise source and reference receiver increase, approaching a limiting value as the distance from source to reference receiver surpasses the acoustic critical distance.
Vibrotactile adaptation enhances amplitude discrimination
Authors: Goble Alan K. , Hollins Mark
Published: October 2005

Human psychophysical detection and amplitude discrimination thresholds for 25-Hz sinusoidal vibrations were measured on the thenar eminence using two-interval forced-choice tracking, in the unadapted state and following exposure to 25-Hz adapting stimuli representing a range of amplitudes (5–25 dB SL). As expected, detection threshold was elevated 6 to 7 dB for each 10-dB increase in the adapting stimulus. In contrast, amplitude difference thresholds for 10 and 20 dB SL standard stimuli were generally lowest when the amplitude of the adapting stimulus was equal to the amplitude of the standard. The results indicate that while adaptation impairs detection of a liminal vibrotactile stimulus, it improves intensity discrimination of supraliminal stimuli that are close in amplitude to the adapting stimulus. The compatability between these results and a recently proposed model of cortical dynamics (Whitsel et al., 1989) suggests that cortical events may contribute significantly to the physiological basis of vibrotactile adaptation.
Intonation of solo violin performance with reference to equally tempered, Pythagorean, and just intonations
Authors: Loosen Franz
Published: October 2005

The purpose of this study was to determine which musical scale best models the solo performances of violinists when they play diatonic scales of C major very slowly and without frequency vibrato as accurately as possible. Eight professional violinists played without stopping three adjacent scales in ascending order (from C4 to C7), followed immediately by an analogous return to the initial note C4 in descending order. Results show that when violin performances are analyzed taking into account the context of the scale in which they were played, Pythagorean and equally tempered scales are equally good models for the description of performances. Just intonation fits the data significantly less well. When the data analysis is limited to the intervals between separate pairs of notes, not taking into consideration the context of the scale in which they were played, observed interval sizes are almost identical to the arithmetic means of the corresponding interval sizes as defined in Pythagorean and equally tempered intonations. Octave intervals calculated by summing the sizes of performed adjacent major and minor seconds within octaves, show an average stretching of 3.9 cents. However, the arithmetic mean of computed interval sizes between two C’s, deviates only 0.3 cents from the theoretical tonal extent of 1200 cents. Results suggest that when scales of C major are played, the tonic C is adopted as an absolute cognitive reference point.
Response to ‘‘Comment on ‘Time domain Doppler estimators of the amplitude of vibrating targets’ ’’ [J. Acoust. Soc. Am. 9
3, 559 (1993)]
Authors: Parker Kevin J.
Published: October 2005

The use of the word ‘‘simplified’’ in the cited paper might be misconstrued. Thus the authors are grateful to Piquette and Van Buren for emphasizing the correct interpretation. It is pointed out, however, that the ‘‘limited range of validity’’ defined by Piquette and Van Buren may not be viewed as ‘‘extremely limited’’ by those whose entire research endeavor is within the limits they define.
A tensorial classification of elastic waves
Authors: Ignaczak Jozef , Rao C. R. A.
Published: October 2005

Pure stress equations of motion of linear homogeneous anisotropic elastodynamics are used to present a classification of the plane stress progressive waves in an infinite body. A plane stress wave is decomposed into ‘‘normal’’ and ‘‘tangential’’ parts with respect to the wave front in such a way that: (i) both parts can propagate with the same velocity, (ii) the total stress energy of the wave is represented by the positive difference between ‘‘normal’’ and ‘‘tangential’’ stress energies, and (iii) pure ‘‘tangential’’ stress wave cannot propagate. The classification is consistent with and complementary to that of the displacement progressive waves, at least for homogeneous isotropic and transversely isotropic elastic media, and provides a number of new properties of the plane progressive waves in a general anisotropic elastic body.
Energy leakage and reflection in slowly varying waveguides
Authors: Kath W. L. , Minzoni A. A. , Kriegsmann G. A. , Reiss E. L.
Published: October 2005

A new technique is presented which is called the method of slowly varying dispersion relations, for approximately determining the modes near cutoff in two-layer slowly varying waveguides. The depth of the upper layer is finite while the lower layer is semi-infinite. The method is presented for the penetration problem, where the density and sound speed ratios are O(1), which was analyzed previously by different methods. It was shown that all of the energy propagating in the upper layer was lost into the underlying layer. The method is also applied to the case where the lower layer is hard and fast compared to the upper layer. It is shown that in this case energy is both lost into the lower layer and reflected back into the waveguide.
Observation of the midfrequency enhancement of tone bursts backscattered by a thin spherical shell in water near the coincidence frequency
Authors: Kaduchak Gregory , Marston Philip L.
Published: October 2005

A prominent feature predicted for the backscattering of tone bursts by thin spherical shells is an enhancement of a guided wave contribution in the midfrequency range [L. G. Zhang et al., J. Acoust. Soc. Am. 91, 1862–1874 (1992)]. This feature may be useful for certain inverse problems and is associated with a strongly coupled slightly subsonic wave denoted by some authors as the a0− wave. The present research gives a comparison between a ray approximation and experiments in which tone bursts having carrier frequencies in the range 35<ka<70 were incident on an empty stainless steel shell in water of radius a. The sphere’s radius to thickness ratio is a/h=43.8. Time records of echoes provided a means for measuring the guided wave contribution distinct from that of the specular reflection. As predicted, the guided wave echo can be over three times the amplitude of the specular echo and the ka dependence generally follows the predicted hump. Echoes manifest structures similar to those calculated by a time domain Fourier synthesis from the partial wave series.
Numerical solution of scattering from a hard surface in a medium with a linear profile
Authors: Spivack M. , Uscinski B. J.
Published: October 2005

The paper is concerned with the scattering of waves incident at grazing angles upon a rough surface on which Neumann boundary conditions apply, when the medium has a linearly varying refractive index. The scattering is governed by an integral equation, which uses a parabolic form of the Green’s function. The numerical solution of this system requires careful analytical treatment of the Green’s function, and the purpose of this paper is to describe the details both of the analysis and the numerical scheme. Some computational results are shown, and the accuracy of the inversion of the integral equation is tested by comparison with an analytical approximation.
On equations for the speed of sound in seawater
Authors: Dushaw Brian D. , Worcester Peter F. , Cornuelle Bruce D. , Howe Bruce M.
Published: October 2005

Long-range acoustic transmissions made in conjunction with extensive environmental measurements and accurate mooring position determinations have been used to test the accuracy of equations used to calculate sound speed from pressure, temperature, and salinity. The sound-speed fields computed using the Del Grosso equation [V. A. Del Grosso, J. Acoust. Soc. Am. 56, 1084–1091 (1974)] give predictions of acoustic arrival patterns which agree significantly better with the long-range measurements than those computed using the Chen and Millero equation [C. Chen and F. J. Millero, J. Acoust. Soc. Am. 62, 1129–1135 (1977)]. The predicted ray travel times and travel time error have been calculated using objectively mapped sound-speed fields computed from conductivity, temperature, depth (CTD) and expendable bathythermograph (XBT) data. Using the measured and predicted ray travel times, a negligible correction to Del Grosso’s equation of +0.05±0.05 m/s at 4000-m depth is calculated.
Expressions of acoustic parameters in organic liquid derived from Schaaff’s theory
Authors: Tong Jie , Dong Yanwu , Tong Tiankui
Published: October 2005

Based on Schaaffs’ theory of ultrasonic speed in an organic liquid, new expressions of acoustic parameters, including those of the temperature coefficient of ultrasonic speed (∂C/∂T)P, the pressure coefficient (∂C/∂P)T, and the nonlinearity parameter B/A were derived and analyzed. It was found that the expressions could generally describe and expound acoustic properties of the liquid, and could even determine the parameters quantitatively. The expressions have two features: (i) they connect the acoustic parameters with the molecular radius of the medium; (ii) they indicate that under atmospheric pressure and at room temperature, the temperature coefficient (∂C/∂T)P is negative while the pressure coefficient (∂C/∂P)T is positive, and under the same conditions the B/A value in an organic liquid always exceeds 8. These results are confirmed by the experimental data from the literature.
Predictions of the dependence of the difference limen on d′
Authors: Hellman William S.
Published: October 2005

The consequences that follow from the conjecture that the decision variable for intensity discrimination does not depend on the d′ value implied by the percentage-correct criterion set for difference limen (DL) measurements are investigated. The analysis is performed within the framework of a Taylor series representation for the level dependence of the decision variable. In this study the decision variable has been identified with the peripheral neural-count function. However, the conclusions are the same with respect to whatever stochastic variable is actually used by the system. The solutions for the neural-count function and the equations obeyed by the DL are obtained to various orders of the Taylor series representation. The assumption of d′ independence constrains the second- and higher-order solutions for the neural-count function to have the same form as predicted in first order. It is found, however, that the dependence of the DL on level and d′ varies with the order of approximation. These alterations are discussed with respect to empirical data. The results of the analysis are not dependent on the detailed structure of the detection and discrimination mechanisms of the auditory system. Thus, the predictions are true for any model compatible with the assumption of d′ independence for the decision variable.
Minimal upward spread of masking: Correlations with speech and auditory brainstem response masked thresholds
Authors: Klein Alan J. , Dubno Judy R.
Published: October 2005

Much less than predicted upward spread of masking, termed undermasking, was previously noted in three elderly listeners, who are the focus of this report. Three aspects of undermasking were studied: Reliability, facilitation of speech recognition in noise, and correlation with physiological measurements. The masker was a 90-dB-SPL 1-kHz low-pass-filtered noise. Reliability of undermasking was assessed from serial measurements made over an approximately 2-year interval. Masked speech thresholds were measured with an adaptive procedure for two types of stimuli: Spondaic words and the California Consonant Test. Subjects with undermasking had substantially lower masked speech thresholds than either audiometrically matched elderly subjects or young, normal-hearing subjects. It appears that undermasking is a stable characteristic that provides the listener with exceptionally good communication abilities in noise. Finally, a strong positive correlation was observed between the masked auditory brainstem response (wave V) threshold and the masked behavioral threshold, suggesting that the mechanism producing undermasking is in the auditory periphery.
Auditory profile analysis of harmonic signals
Authors: Zera Jan , Onsan Zekiye A. , Nguyen Quang T. , Green David M.
Published: October 2005

Spectral shape discrimination for harmonic complexes with 100-, 200-, or 400-Hz fundamental was investigated in two sets of experiments. In the first set, the signal was an increment in a single component of an otherwise equal-amplitude complex. The results of these experiments showed nearly a 30-dB increase in thresholds as the signal frequencies increased from 1000 to 5000 Hz. A transformation of data based on the assumption that the critical detection quantity is the change in the level in a critical band centered at the signal frequency was applied to remove the effects of the nonsignal components. The corrected thresholds have a bowl-like shape similar to that seen in studies of spectral shape discrimination of stimuli with components equally spaced on a logarithmic frequency scale. Additional experiments examined the effects of the number of components in the complex and the relative phase of the components of the harmonic complex. In the second set of experiments, the effects of local masking were examined either by increasing the level of several adjacent components, or by removing nonsignal components near a single signal component. Again, the results with harmonic signals are similar to those obtained with components spaced at equal intervals on a logarithmic frequency scale, if one calculates the increment in the level produced in a critical band centered at the signal frequency.
Modulation detection interference: Some spectral effects
Authors: Bacon Sid P. , Moore Brian C. J.
Published: October 2005

Several experiments are described in which the threshold for detecting 10-Hz amplitude modulation (AM) of a 2000-Hz signal carrier was measured in the presence of a masker that consisted of one to ten carrier frequencies. The masker was either unmodulated or amplitude modulated at a depth of 0.5 and a frequency of 10 Hz. In experiment 1, threshold was measured as a function of the frequency of a single masker carrier. The patterns of the interference effect were similar whether the masker was modulated or not, suggesting that some of the interference was due to a within-channel effect (spread of excitation). In experiment 2, it was shown that a masker consisting of two carrier frequencies could produce more interference than either carrier alone. However, there was generally no additional interference when more than two carriers were presented, at least up to the ten tested here (experiments 3 and 4). In experiment 5, the masker carrier frequencies were either harmonically or nonharmonically related to the signal carrier frequency. There was little difference in the size of the interference effect between the two maskers, suggesting that harmonicity may not play an important role in modulation detection interference.
Self-organized acoustic feature map in detection of fricative-vowel coarticulation
Authors: Leinonen Lea , Hiltunen Tapio , Torkkola Kari , Kangas Jari
Published: October 2005

The self-organizing map, a neural network algorithm of Kohonen, was used for the detection of coarticulatory variation of fricative [s] preceding vowels [a:], [i:], and [u:]. The results were compared with the psychoacoustic classification of the same samples to find out whether the map had extracted perceptually meaningful features of [s]. The map distinguished samples of [s] in front of [u:] from those in front of [a:] or [i:] throughout the fricative duration. Samples of [s] preceding [a:] and [i:] were distinguished from each other only just before (about 40 ms) the vowel onset. The results agreed with the perceptual classifications. Most judgments (82%) of [s] in front of [u:] were correct, and this variant of [s] was recognized from the first and second halves of segmented fricatives equally well. Samples of [s] in front of [a:] and [i:] were distinguished from each other less accurately. When halves of segmented [s] were perceptually judged, the differentiation between the following [a] and [i] was possible only on the basis of the second half of the fricative. The results demonstrate that the self-organizing map is a useful tool for the extraction of intersubject regularities in speech spectra. The map also provides an easily understandable, on-line, visualization of speech that can be used as feedback in therapy and education.
A biologically inspired control approach for distributed elastic systems
Authors: Fuller C. R. , Carneal J. P.
Published: October 2005

A multi-degree of freedom control approach, which is largely inspired by biological systems, is presented. Control inputs to a structure are achieved by multiple piezoelectric actuators. One actuator chosen as the ‘‘master’’ actuator is under the direction of the central, sophisticated controller. The other ‘‘slave’’ actuators derive their control inputs by localized, simple learning rules related to the behavior of their neighbor actuators including the ‘‘master.’’ Simulations on the control of the vibrational energy density of a harmonically excited simply supported beam demonstrate a significant improvement in control performance over a single actuator case, particularly for off-resonance frequencies. Thus high attenuations are achieved with a multiple degree of freedom actuator with a single main channel of control.
Regularity of cochlear nucleus stellate cells: A computational modeling study
Authors: Hewitt Michael J. , Meddis Ray
Published: October 2005

This article reports on a computational modeling study designed to investigate the generation of the transient chopper response of cochlear nucleus stellate cells. The model is based on a simulation of the auditory periphery which feeds a generic stellate-cell model. Physiological recordings of transient chopper units in response to short, best frequency, tone bursts show a brief initial period (typically <10 ms) of rapid rate adaptation as evidenced by a rapid rise in mean interspike interval. Associated with this rate adaptation is a significant increase in firing irregularity. The changes in rate and irregularity have recently been attributed to the activation of noisy inhibitory inputs on the cell [e.g., Banks and Sachs, J. Neurophysiol. 65, 606–629 (1991)]. However, the results show that the transient chopper response pattern can be generated without the need for inhibitory inputs. The transience of the initial chopping pattern is sensitive to the following model parameters: (a) the firing threshold of the cell, (b) the number of excitatory inputs that converge on the cell, and (c) the magnitude of the current delivered to the cell for each active input. The response was also found to be relatively insensitive to changes in the degree of dendritic filtering imposed on the auditory-nerve input. The results of each simulation can be explained by considering the pattern of depolarization the cell receives during the course of a tone burst.
On the origin of the enlarged melodic octave
Authors: Hartmann William Morris
Published: October 2005

The perceptual octave is larger than the physical octave, i.e., most listeners perceive that two tones are an octave apart when their frequency ratio is greater than 2. This result is known as the octave enlargement effect. There are two theories for the effect, one of them a central template theory, the other a peripheral timing theory. In principle, it is possible to determine which theory is better by discovering whether or not octave enlargement occurs for centrally generated dichotic pitches such as the Huggins pitch. Experiments show that octave enlargement does indeed occur for Huggins pitch. This is the result predicted by the central template theory, but it can be argued that the result does not entirely eliminate the timing theory. A detailed examination of the two theories shows that each requires revision in order to make the octave enlargement prediction follow logically from its premises. The central template theory requires the auditory system to differentiate excitation caused by different harmonics of a complex tone on some basis other than place of excitation. Neural synchrony is suggested as a basis. The timing theory, originally formulated in terms of a neural interspike interval timing, can be made internally consistent by replacing the neural interspike-interval circuit by a neural autocorrelator.
Active and passive acoustic behavior of bubble clouds at the ocean’s surface
Authors: Prosperetti A. , Lu N. Q. , Kim H. S.
Published: October 2005

The emission and scattering of sound from bubble clouds is studied theoretically. It is shown that clouds having a size and air content similar to what might be expected as a consequence of the breaking of ocean waves can oscillate at frequencies as low as 100 Hz and below. Thus cloud oscillations may furnish an explanation of the substantial amount of low-frequency wind-dependent oceanic ambient noise observed experimentally. Detailed results for the backscattering from bubble clouds—particularly at low grazing angles—are also presented and shown to be largely compatible with oceanic data. Although the cloud model used here is idealized (a uniform hemispherical cloud under a plane water free-surface), it is shown that the results are relatively robust in terms of bubble size, distribution, and total air content. A similar insensitivity to cloud shape is found in a companion paper [Sarkar and Prosperetti, J. Acoust. Soc. Am. 93, XXX (1993)].