bluuebunny/crossref_metadata_2025 huggingface dataset:
Listener adaptive characteristics of vowel devoicing in Japanese dialogue
Authors: Imaizumi Satoshi , Hayashi Akiko , Deguchi Toshisada
Published: October 2005

Listener adapative characteristics of Japanese vowel devoicing were investigated by analyzing (i) dialogues between professional teachers and hearing-impaired (HI) or normal-hearing (NH) children, and (ii) speech samples read by the teachers as fast and clearly as possible (RD). The teachers reduced the devoicing rate and lengthened the moras more in the HI vs NH samples, and even more in the HI vs RD samples. A logistic regression analysis of the devoicing rate suggests that the speech rate dependency of the devoicing rate is different among the HI, NH, and RD samples. When moras are lengthened, the predicted devoicing rate decreases more for the HI vs NH samples, and even more in the HI vs RD samples, suggesting that not only rate-dependent adjustments but also rate-independent adjustments significantly affect devoicing reduction. These results suggest the following: (1) Professional teachers of hearing-impaired children reduce their devoicing not only by lengthening the interval of successive voicing/devoicing gestures, but also by resizing component gestures to some extent, probably to improve the listener’s comprehension; (2) vowel devoicing should be represented in terms of parameters of speech motor control; (3) it may be possible to develop an optimized communication method for hearing-impaired children by simulating such listener-adaptive adjustments in speech production.
Perceptual separation of concurrent speech sounds: Absence of across-frequency grouping by common interaural delay
Authors: Culling John F. , Summerfield Quentin
Published: October 2005

Three experiments and a computational model explored the role of within-channel and across-channel processes in the perceptual separation of competing, complex, broadband sounds which differed in their interaural phase spectra. In each experiment, two competing vowels, whose first and second formants were represented by two discrete bands of noise, were presented concurrently, for identification. Experiments 1 and 2 showed that listeners were able to identify the vowels accurately when each was presented to a different ear, but were unable to identify the vowels when they were presented with different interaural time delays (ITDs); i.e. listeners could not group the noisebands in different frequency regions with the same ITD and thereby separate them from bands in other frequency regions with a different ITD. Experiment 3 demonstrated that while listeners were unable to exploit a difference in interaural delay between the pairs of noisebands, listeners could identify a vowel defined by interaurally decorrelated noisebands when the other two noisebands were interaurally correlated. A computational model based upon that of Durlach [J. Acoust. Soc. Am. 32, 1075–1076 (1960)] showed that the results of these and other experiments can be interpreted in terms of a within-channel mechanism, which is sensitive to interaural decorrelation. Thus the across-frequency integration which occurs in the lateralization of complex sounds may play little role in segregating concurrent sounds.
Zooplankton target strength: Volumetric or areal dependence?
Authors: Demer David A. , Martin Linda V.
Published: October 2005

Target strengths (TS) of various zooplankton were measured at 200 kHz, 420 kHz, and 1 MHz and the dependence of these data on animal volume versus cross-sectional area was explored. The 420-kHz and 1-MHz data were collected with a dual-beam sonar system and the 200-kHz data with a split-beam system. Experiments were conducted with live, tethered individuals in an enclosure filled with filtered seawater. The data were compared to both empirical and theoretical models of reduced target strength (TS normalized by the square of the animal length) versus ka (the product of wave number and equivalent cylindrical radius). The theoretical models chosen for this comparison were two versions of a high-pass bent-cylinder model (Stanton, 1989b) that indicate TS is dependent on animal volume, and the ray bent-cylinder model (Stanton, 1993a) which implies TS is dependent on the cross-sectional area. The dependence of acoustic backscattering on animal volume or area was tested by fitting regression lines for TS versus the logs of ka, length (L), wet weight (WW), and dry weight (DW). Contrary to an empirical model derived from similar experiments (Wiebe et al., 1990), and to the high-pass models, the regressions indicated that TS is proportional to the cross-sectional area of the animal. However, because scattering from individual zooplankton is highly nonlinear, especially in the geometric scattering region (ka≳1), linear regressions of TS versus the log of ka, L, WW, or DW can be misleading. Furthermore, neither Wiebe et al. (1990) nor this experiment directly accounted for animal orientations. Simulations using a distorted-wave Born-approximation model (Chu et al., 1993), indicated that animal behavior is an important factor in the scattering characteristics of zooplankton. Different distributions of animal tilt angle can influence the general trend of the TS model to exhibit either areal or near volumetric dependence.
Low-frequency sound propagation modeling over a locally reacting boundary with the parabolic approximation
Authors: Robertson J. S. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

There is substantial interest in the analytical and numerical modeling of low-frequency, long-range atmospheric acoustic propagation. Ray-based models, because of their frequency limitations, do not always give an adequate prediction of quantities such as sound-pressure or intensity levels. However, the parabolic approximation method, widely used in ocean acoustics and often more accurate than ray models for frequencies of interest, can be applied to this type of acoustic propagation in the atmosphere. Modifications of an existing implicit finite-difference implementation for computing solutions to the parabolic approximation are discussed. A locally reacting ground surface is used with one- and two-parameter impedance models, while a nonreflecting boundary condition is used to handle the upper boundary. Relative sound-pressure level calculations are performed for a number of flow resistivity values in both homogeneous and nonhomogeneous atmospheres. Comparisons to experimental data are made which suggest this modeling approach can be useful in the study of these types of propagation problems.
The speed of a wave along a fluid/solid interface in the presence of anisotropy and prestress
Authors: Norris Andrew N. , Sinha Bikash K.
Published: October 2005

The classical solution for the Scholte wave along a fluid and isotropic substrate is well known. However, when the substrate is either a weakly anisotropic solid, or the adjoining fluid is subject to a hydrostatic pressure, the analysis of Scholte wave propagation becomes rather complex and lengthy computations are required to obtain the solution. The purpose of this paper is to apply simple and computationally efficient expressions in the determination of Scholte wave speeds for substrates with either weak anisotropy or in the presence of uniform initial stresses and strains in the substrate and fluid media. Both of these two simple expressions are for the incremental change in the Scholte wave speed Δv/v from an appropriately selected isotropic, reference substrate and adjoining fluid under no hydrostatic pressure. The predictions of the Scholte wave speeds from the derived expressions agree to well within 1%–2% with the other approximation techniques for the high-frequency asymptotes of the Stoneley wave velocity dispersions in a fluid-filled borehole traversing either a weakly anisotropic formation or a formation with initial stresses and strains caused by a borehole pressurization.
Spherical expansions of time-domain acoustic fields: Application to near-field scanning
Authors: Hansen Thorkild B.
Published: October 2005

This paper addresses the problem of formulating spherical near-field scanning for time-domain acoustic fields. Two basic spherical expansions for time-domain acoustic fields are derived that determine the field outside a scan sphere enclosing the source region. The first expansion is obtained with the help of Green’s second identity, the scalar free-space Green’s function, and the Fourier transform. This expansion expresses the time-domain acoustic field outside the scan sphere in terms of the time-domain acoustic field and its normal derivative on the scan sphere. The second expansion is a spherical eigenfunction expansion that expresses the time-domain acoustic field outside the scan sphere directly in terms of the time-domain acoustic field on the scan sphere. Then a probe-corrected formula is presented that expresses the field outside the scan sphere in terms of the output of a known axis-symmetric probe on the scan sphere. Sampling theorems that determine the distance between spatial sample points on the scan sphere and the distance between time-sample points are also derived. The sampling theorems show how to compute the field everywhere outside the scan sphere in terms of space-time samples of the field on the scan sphere or in terms of the probe output on the scan sphere. Finally, a numerical example illustrates the use of the eigenfunction expansion and the corresponding sampling theorem.
Sound–structure interaction analysis of composite panels using coupled boundary and finite element methods
Authors: Pates C. S. , Shirahatti U. S. , Mei C.
Published: October 2005

Sound–structure interaction problems frequently arise in the aerospace and automotive industries. In this paper, the boundary element method is coupled with the finite element method to accurately model sound–structure interaction of a composite panel resting on an acoustic cavity. First, the approach is validated by comparing the numerical solutions with known analytical and experimental results for isotropic panels. However, for composite panels, exact solutions are difficult or impossible to compute. Also, until today, very little effort has been made to obtain experimental results for composite panels undergoing sound–structure interaction. As the first step toward exploring this area of sound–structure interaction, this study offers numerical results on an acoustic cavity-backed composite panel by harnessing the strengths of the coupled BEM–FEM technique. The results indicate that the transmission loss values for composite panels are very sensitive to the lamination angle of the fibers in the different layers of the composite panel.
Pre-stressing a Tonpilz transducer
Authors: Bodholt Helge
Published: October 2005

Tonpilz transducers have a center bolt to prevent the ceramic being subjected to a tensile stress during part of the alternating stress cycle. Two points in the transducer design are analyzed; one is the calculation of the peak stress (the method presented used the voltage applied to the ceramic during the transmitter pulse, and measured values of the electrical admittance of the transducer), the other is the control of the pre-stress imposed by the center bolt. The pre-stress should be larger than the calculated peak alternating stress, and it can be controlled by measuring the voltage or the charge generated when the bolt is tightened.
Low-frequency acoustic backscattering by volumetric inhomogeneities in deep-ocean sediments
Authors: Tang Dajun , Frisk George V. , Sellers Cynthia J. , Li Dan
Published: October 2005

An experiment to study acoustic backscattering from deep-ocean sediments was conducted in July 1993 as part of the Acoustic Reverberation Special Research Program sponsored by the Office of Naval Research. An acoustic source transmitting chirp signals in the frequency range 250–650 Hz and a 24-element vertical receiving array attached to the source were suspended near the seafloor over a sediment pond in the vicinity of the Mid-Atlantic Ridge. The array steered in the normal incidence (endfire) direction is used to determine the sediment structure, while the array steered at oblique angles is used to determine backscattering strength. It is found that the sediment is stratified with gentle horizontal changes, except for two irregular regions, with thicknesses of about 20 m, located approximately 18 and 60 m beneath the seafloor. These inhomogeneous regions are shown to be the dominant influence on the backscattered field, and the backscattering strength of each region as a function of grazing angle is estimated. It is found that the removal of coherent reflections from subbottom stratified layers is essential to the analysis of bottom backscattering phenomena.
A model for high-frequency acoustic backscatter from gas bubbles in sandy sediments at shallow grazing angles
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: October 2005

A model for acoustic backscatter from trapped bubbles in sandy sediments was developed. The model combines a Biot acoustic penetration model with a resonance scattering mechanism from trapped bubbles. The bubble size distribution is assumed to mirror the size distribution of the fluid pores that exist between sand grains. An estimate of the pore size distribution is constructed from the grain size distribution, based on the known pore structure between dense random packings of hard spheres. The principle of acoustic reciprocity is employed to compute backscattered acoustic pressure in terms of the incident pressure and the scattering cross section of a bubble distribution. The model is applied to data from experiments recently taken at sea. It is concluded that trapped gas is often a likely cause of observed backscatter from sandy sediments. Very small amounts of gas appear to be sufficient to produce significant backscatter.
The mean acoustic field in layered media with rough interfaces
Authors: Berman David H.
Published: October 2005

An algorithm is presented for determining the mean acoustic field in a layered medium containing rough interfaces. It is assumed that scattering by the rough interfaces when considered separately and in the absence of sound speed and density variation can be well-approximated. It is also assumed that propagation in layered media with flat interfaces can be well approximated. The present work shows how these results can be combined to yield the mean field in a stack of layers with variable sound speeds and densities which are separated by rough interfaces.
Nonperturbative modal tomography inversion. Part II. Numerical simulation
Authors: Shang E. C. , Wang Y. Y. , Jones R. M. , Georges T. M.
Published: October 2005

In a previous paper [Jones et al., J. Acoust. Soc. Am. 94, 2296–2302 (1993)], it has been shown that implementation of nonperturbative modal ocean acoustic tomography based on the Abel transform requires only to determine an integer Nm0 (equal to the number of convergence zones between the source and receiver) from modal travel time and modal phase difference measurements. This integer Nm0 can be estimated by using climatological data or by using a ‘‘dual point’’ measurement scheme for a range-independent case as proposed in this paper. Numerical simulations of inversions both for a range-independent (RI) case and a range-dependent (RD) case are presented. Finally, the error of the Abel transform inversion is discussed.
A note on pure-longitudinal and pure-shear waves in cubic crystals
Authors: Zuo Q. H. , Schreyer H. L.
Published: October 2005

The acoustic tensor of a general anisotropic material is derived using the spectral representation of the elasticity tensor, an approach that makes the contribution from each projection operator more visible than the customary approach of using matrix components of the elasticity tensor. As an application of the approach, the acoustic tensor for a cubic crystal is explicitly formulated, and the directions for which purely longitudinal or shear waves can propagate are found rigorously. The result proves that the directions stated by Thurston are indeed the only ones along which pure waves can exist.
Reply to ‘‘Comments on ‘Sound radiation from finite cylindrical coated shells, by means of asymptotic expansion of three-dimensional equations for coating’ ’’ [J. Acoust. Soc. Am. 97, 656–657 (1995)]
Authors: Laulagnet B. , Guyader J. L.
Published: October 2005

A response to comments made by J. Gregory McDaniel in a Letter to the Editor commenting on the paper ‘‘Sound radiation from finite cylindrical coated shells, by means of asymptotic expansion of three-dimensional equations for coating’’ is presented.
Ultrasonic velocity and absorption measurements for poly(acrylic acid) and water solutions
Authors: So Jin H. , Esquivel-Sirvent R. , Yun S. S. , Stumpf F. B.
Published: October 2005

The ultrasonic velocity and absorption at 21 MHz and the shear viscosity were measured for poly(acrylic acid) and water solutions, as a function of concentration and temperature. The concentrations used were 1, 3, 5, 9% by weight and the temperatures were 25 °, 30 °, 35 °, 40 °, 45 °C. It was found that the velocity increases with the concentration and temperature. The absorption α/f2 decreased with increasing temperature and increased with increasing concentration. The shear viscosity decreased with temperature and increased with concentration.
Local active control of diffracted diffuse sound fields
Authors: Garcia-Bonito J. , Elliott S. J.
Published: October 2005

The average spatial extent of the zone of quiet created by a local active control system in a diffuse enclosed sound field has been investigated using computer simulation and measured experimentally. The secondary source is modeled as a rigid sphere with a pulsating segment and its diffracting effect on a diffuse primary pressure field has been simulated. The diffraction effects of a hypothetical listener’s head, modeled as rigid sphere, on both the primary and secondary acoustic fields have also been calculated using a least-squares calculation for the amplitudes of a set of spherical harmonics. The size of the average zone of quiet is observed to increase slightly as a result of diffraction of the secondary field by the rigid sphere. The calculations give a good prediction of the average zones of quiet measured experimentally, both with and without a diffracting sphere present.
Acoustical principles of a dynamic compressibility apparatus with internal reference
Authors: Edmonds David E. , Nolle A. W.
Published: October 2005

McKinney, Edelman, and Marvin [J. Appl. Phys. 27, 425 (1956)] described an apparatus for dynamic compressibility measurement consisting of a small pressure chamber containing two piezoelectric transducers, a liquid of known compressibility, and the sample. Several investigators have used this system, sometimes in slightly modified form, in studies of polymers. However, since a fully calibrated measurement requires assembling the chamber three times, results can be vitiated by change of transducer properties in pressure–temperature cycling or by failure to reproduce assembly conditions. These problems are avoided in a new apparatus, suitable for frequencies from a few hertz to more than 1000 Hz. It provides calibrated results from measurements taken quickly at any chosen pressure and temperature, without reassembly. There is a central chamber with transducers, a side chamber with sample, and a similar side chamber containing only liquid. A moveable partition is used to let the central chamber communicate acoustically with either side chamber, or both. Operating equations are derived. Also analyzed and studied is the behavior of the system with increasing frequency as the quasistatic approximation breaks down. Test data on poly(vinyl acetate) are shown.
Acoustic reflectivity of a sandy seabed: A semianalytic model of the effect of coupling due to the shear modulus profile
Authors: Hall Marshall V.
Published: October 2005

Acoustic transmission loss in shallow water is sensitive to the reflectivity of the seafloor, which is affected by the shear modulus profile. To demonstrate this effect, marine sand is modeled as a viscoelastic medium in which the shear modulus has a power-law dependence on depth [G(z)∝zp]. Such a medium is heterogeneous, so the shear and compressional displacement potentials do not in general satisfy separate wave equations. Determination of reflectivity therefore requires either that the seabed be divided into a stack of homogeneous layers, or that the equations of elastic motion in a heterogeneous solid be analyzed fundamentally. The latter is achieved using the method of weakly coupled potentials. Coupled differential equations for the P and S potentials are derived, and an expression for reflectivity is obtained that depends on the P, but not the S, potential [providing G is modified near z=0 such that G″(0)=0]. The P equation is solved by invoking the Born approximation. The model is applied to six profiles [1≥p≥0.40], and the resulting reflectivities at frequency 10 Hz are compared with SAFARI results for the corresponding layer-stack profiles. Good agreement is obtained for p≥0.5, but as p progresses below 0.5 the agreement deteriorates, apparently because the requirements of the Born approximation are progressively unsatisfied.
Remote determination of in situ sediment parameters using Love waves
Authors: Bautista Edgar O. , Stoll Robert D.
Published: October 2005

In situ properties of near-bottom sediments are determined using an experimental technique based on the dispersive properties of horizontally polarized surface waves generally known as Love waves. This technique basically consists of generating the Love waves, analyzing the recorded seismic signals to determine dispersion, and, finally, mathematically inverting the dispersion data to obtain a geoacoustic model of the sediment. In the field experiments, Love waves are generated using a torsional source and the generated signals are recorded with a linear array of gimbaled geophones that measure transverse horizontal motion. Experimental dispersion curves (wave velocity versus frequency), are then obtained from the recorded wavelets. These velocity waveforms are usually composed of overlapping modes and in order to reduce the influence of modal interference on the experimental phase velocity dispersion curves, a phase-matched filter is used to extract a smoothed phase velocity dispersion curve for the fundamental mode. The dispersion curve is then mathematically inverted to obtain a sediment model using a constrained least-squares method with singular-value decomposition and it is shown that the maximum parameter resolution depth can be estimated from the generalized inverse. Practical use of the technique is demonstrated by an analysis of the results of a field experiment carried out in a marine sand sediment.
Acoustic scattering from a fluid-loaded cylindrical shell with discontinuities: Single plate bulkhead
Authors: Cuschieri J. M. , Feit D.
Published: October 2005

The far-field acoustic scattered pressure from a fluid-loaded cylindrical shell with an internal plate bulkhead is determined from knowledge of the junction forces between the shell and the internal structure, for the circumferential modes n equals 0 and 2. The n equals 2 case is representative of results, such as the presence of compressional and shear helical waves, for which n is greater than zero. The junction forces are determined using a mobility (impedance) matrix approach, which matches the response of the shell to that of the plate bulkhead at the junction, together with an input of the shell-free response under the influence of obliquely incident acoustic waves. For n equals 0, if the angle of incidence of the acoustic wave is less than approximately 16 deg, for a steel shell in water, the scattered pressure has significant contributions from the supersonic longitudinal axial waves in the shell. For greater angles of incidence, the scattered pressure has comparable contributions from the axial waves and the junction radial load. The tangential shear waves do not contribute in the n equals 0 case.

For n greater than 0, if the angle of incidence is less than approximately 30 deg, then the scattered pressure is dominated by the contributions from the supersonic longitudinal axial and tangential shear waves, above the cut-on frequency. Below the cut-on frequency of these waves, the far-field scattered pressure is dominated by the component associated with the radial junction force. For angles of incidence greater than approximately 30 deg, the radial junction force and the shear and longitudinal waves equally contribute. There is, however, a difference in the radiation characteristics of these components. While the contribution from the radial force has a dipole directivity pattern, the contributions from the shear and longitudinal waves have a preferred direction of propagation, since both of these waves are supersonic. The contribution from the junction moment is always insignificant when compared to the other components. Finally, the results show that for very low frequencies, the in-plane response of the plate bulkhead is very small and the junction between the plate and the shell behaves similar to a radially pinned junction. As the frequency increases, the internal structure has in-plane resonances and the radial influence of the bulkhead is at a minimum. At these frequencies, the contribution from the radial forces to the far-field pressure is minimal.
Acoustic, acoustics
Authors: Beyer Robert T.
Published: October 2005

The origins of the words ‘‘acoustic,’’ ‘‘acoustics’’ are traced.
Speckle structure in three dimensions
Authors: Bashford Gregory R. , von Ramm Olaf T.
Published: October 2005

Ultrasound speckle has long been recognized as a noise source in diagnostic imaging. The advent of three-dimensional imaging and flow detection requires the characterization of the three-dimensional acoustical speckle pattern. Ultrasound data were acquired by using an automated three-dimensional translation stage to measure the radio-frequency (rf) backscatter signals from a volume scattering phantom. The data samples were processed off-line to locate and measure envelope-detected speckle peaks, i.e., local maxima. Results indicate that speckle has a distinctive structure in which three-dimensional peaks can be located and measured. These peaks are brighter on average than the mean speckle brightness level and are uniformly distributed throughout the volume. The lateral breadth of the speckle peaks, defined as the breadth of the −6 dB contour in the lateral-elevational plane, is over twice the width predicted by previous investigators. This is the first attempt to physically measure the breadth of bright spots in the speckle pattern. A rational for the discrepancy between previous theory and the measurement in this paper is given.
State space boundary element–finite element coupling for fluid–structure interaction analysis
Authors: Giordano Jeffery A. , Koopmann Gary H.
Published: October 2005

State space coupling is a new approach for handling computational fluid–structure interaction problems in the low to medium frequency range. The method is based on standard boundary element (BEM) and finite element (FEM) discretizations of the acoustic and structural domains, respectively. The implicit frequency dependence of a traditional acoustic impedance matrix is made explicit through a power series expansion on circular frequency and considering time harmonic motion. Once expanded, the acoustic energy of the fluid is directly coupled to that of the structure via Hamilton’s principle. The coupled system is then recast in a canonical state space form which is also in the form of a standard eigenvalue problem. Solution of this system produces a series of complex eigenvalues and eigenvectors which represent a modal decomposition of the fluid-loaded structure. Biorthogonality properties of the state space eigensystem allow for an uncoupled, modal solution of the forced problem. Results for a submerged spherical shell and a finite plate in an infinite ridged baffle are given to illustrate the state space approach.
Active control of structurally radiated sound using multiactuator method
Authors: Feng Leping
Published: October 2005

A multiactuator method is suggested in this paper. Attempt is made to integrate the ideas of the optimization of control forces and the optimization of actuator positions. Instead of a conventional multichannel controller, one control channel is used to control many actuators. An array of actuators is prepositioned on the structure. One actuator is chosen as master actuator that is always active. With the same output, all of other actuators are tested one by one in three different states: in phase, out of phase, or just switched off according to different primary excitations. The state that minimizes cost function is then taken as the state of that actuator. The output of control force is reoptimized in each of the tests. The final optimized control force is obtained when all of actuators are tested. The optimization is performed by the conventional feedforward approach. With this method it is possible to control many modes by using an ordinary SISO controller. The mechanism behind this approach is examined. Numerical examples are provided. For a baffled, simply supported plate with 25 modes, the noise power reduction of the suggested method is 15–20 dB higher than that of the single actuator method.
A fully mechanical linear transducer model with application to generalizing the nonlinear Hunt electrostatic transducer for harmonic and transient suppression
Authors: Piquette Jean C.
Published: October 2005

The Hunt electrostatic transducer model [F. V. Hunt, Electroacoustics (Wiley, New York, 1954), pp. 176–177] is generalized for radiation loading by analogy with a fully mechanical transducer model which is developed here. The fully mechanical transducer model is developed by analogy with a simple equivalent circuit. The radiation loading considered exactly models the radiation impedance of a spherical transducer immersed in fluid. A method for driving the generalized Hunt model at high voltage in such a way that no harmonics or transients appear in the radiated waveform is described. The results presented may be useful in developing models for transducers containing lead magnesium niobate (PMN) or lead magnesium niobate-lead titanate (PMNPT) active elements, and for developing methods for driving such transducers at high amplitude in a harmonic- and transient-suppressed manner.
Nonlinear wave propagation in horns and ducts
Authors: Klippel Wolfgang
Published: October 2005

The one-parameter sound field of finite amplitude is modeled by an acoustic transmission line model and by block-oriented system models containing dynamic linear and static nonlinear subsystems. The transmission line model is based on conical elements and each element is represented by a linear four-port and a nonlinear source of volume velocity derived from the nonlinear wave equation in Lagrangian coordinates. The block-oriented system model with a lattice structure shows the forward and backward propagating sound-pressure waves separately. A simplified overall model and the derived higher-order system functions based on the Volterra approach describe the relation between the sound pressure at two points in the sound field. The presented models are the basis for numerical simulations, nonlinear system identification, and signal processing related to the nonlinear sound propagation in horns, ducts, and other acoustical systems with a nearly one-parameter sound field.
Neural network modeling of a dolphin’s sonar discrimination capabilities
Authors: Au Whitlow W. L. , Andersen Lars N. , Rasmussen A. René , Roitblat Herbert L. , Nachtigall Paul E.
Published: October 2005

The capability of an echolocating dolphin to discriminate differences in the wall thickness of cylinders was previously modeled by a counterpropagation neural network using only spectral information from the echoes. In this study, both time and frequency information were used to model the dolphin discrimination capabilities. Echoes from the same cylinders were digitized using a broadband simulated dolphin sonar signal with the transducer mounted on the dolphin’s pen. The echoes were filtered by a bank of continuous constant-Q digital filters and the energy from each filter was computed in time increments of 1/bandwidth. Echo features of the standard and each comparison target were analyzed in pairs by a counterpropagation neural network, a backpropagation neural network, and a model using Euclidean distance measures. The backpropagation network performed better than both the counterpropagation network, and the Euclidean model, using either spectral-only features or combined temporal and spectral features. All models performed better using features containing both temporal and spectral information. The backpropagation network was able to perform better than the dolphins for noise-free echoes with Q values as low as 2 and 3. For a Q of 2, only temporal information was available. However, with noisy data, the network required a Q of 8 in order to perform as well as the dolphin.
Influence of interfacial slits with elastic slip on the propagation of SH waves
Authors: Chevalier Y. , Louzar M. , Maugin G. A.
Published: October 2005

This work examines the influence of various parameters, especially the effect of elastic slip at a single slit or a periodic array of slits situated at the interface between two isotropic elastic media on the propagation of waves. The analysis consists of transforming the formulation of the problem into an integral equation for the jump of the diffracted elastic displacement, at the interface, and solving this numerically after decomposition into Chebyshev polynomials and truncation of the resulting infinite series by use of an energy conservation criterion. The effects are illustrated on two characteristic features, the polar diagram of the amplitude of the far-field diffracted displacement, and the transmission and reflection coefficients. The features revealed provide an indication of the usefulness of the results in assessing the quality of bonding at interfaces via a wave-analysis technique.
Phase-space marching algorithm in the presence of a planar wave velocity discontinuity—A qualitative study
Authors: Steinberg Ben Zion , Birman Raz
Published: October 2005

The methodology of marching phase-space transformations has been previously considered for slowly varying media. The present work implements the approach for a medium with a planar wave velocity discontinuity. It is shown that propagation in the water column can be systematically separated from the scattering events at the discontinuity. The latter take place in a narrow interaction zone, out of which the previously invoked local homogeneity assumption can be used again. The width of the interaction zone is obtained by the investigation of the recently developed evolution equation of the local spectra. The associated phase-space propagators and the isolation of phenomena such as reflection, refraction, and head waves in phase space are demonstrated. Computations are performed and compared to reference solutions.
Separation of longitudinal and transverse waves in elastic scattering using finite difference methods
Authors: Stacey Richard
Published: October 2005

It is shown how to augment current finite difference formulations for modeling pulse-echo scattering in an elastic solid with simple techniques that calculate the various longitudinal and transverse wave components separately. The separation techniques are used in an investigation of the scattering from a point source on the transducer axis. The structure of the scattered waves is much clearer when the components are separated, and there is also insight into the different contributions to the echo signal itself. The techniques generalize to other situations and coordinate systems.
Subjective evaluation of new room acoustic measures
Authors: Soulodre Gilbert A. , Bradley John S.
Published: October 2005

A series of experiments were conducted to evaluate several acoustical measures as predictors of subjective judgments. Subjects were asked to rank binaurally reproduced sound fields in terms of loudness, clarity, reverberance, bass, treble, envelopment, apparent source width, and overall preference. The binaural impulse responses were measured in several North American concert halls and were chosen so as to cover as broad a range as possible of RT, EDT, C80, G, IACC, and LF values. The results of these tests were then correlated with the various octave-band objective measures to find the best predictor of each subjective parameter. New objective quantities were found that are correlated with loudness, clarity, bass, and treble judgments. The relative importance of the various subjective parameters to the overall preference of these sound fields was also examined.
A boundary-element-based optimization technique for design of enclosure acoustical treatments
Authors: Yang T. C. , Tseng C. H. , Ling S. F.
Published: October 2005

An effective design tool was developed in this study for solving the acoustical treatments in enclosures at low frequencies. The boundary element method was used for accurately predicting sound fields of an acoustical system. The sequential quadratic programming was selected as the continuous design variable optimizer as a result of its robustness and rapid convergence. In coping with the noncontinuous design variables, the optimizer was enhanced by a modified branch and bound procedure. A small two-dimensional cavity and an irregularly shaped car cabin were applied to demonstrate the utilities of the proposed design tool. Computer simulations indicated that at a low frequency, where enclosures can properly be termed as tightly coupled, purely reactive acoustical treatments are generally preferred at resonances or near-resonances of the two-dimensional cavity as well as at the frequency of interest in the car cabin. The general agreement between this study and previous work [R. J. Bernhard and S. Takeo, J. Acoust. Soc. Am. 83, 2224–2232 (1988)] could be considered adequate for the proposed tool to be utilized for preliminary design studies of acoustical treatments in enclosures. Furthermore, in the case of multiple patching, the optimal locations of acoustical treatments would always contain the region of dominantly acoustical influence. However, simultaneous capability of optimizing locations and impedances of acoustical material were not considered in the previous work.
Suppression tuning characteristics of the 2 f1−f2 distortion-product otoacoustic emission in humans
Authors: Kummer Peter , Janssen Thomas , Arnold Wolfgang
Published: October 2005

The suppression tuning properties of the 2 f1−f2 distortion-product otoacoustic emission (DPOAE) were measured in 16 ears of normally hearing human subjects. DPOAE were elicited by fixed, low-level primary tones in four frequency regions with the second primary tone frequency f2 at 1, 2, 4, and 6 kHz. For various suppressor frequencies, suppression of the DPOAE was measured as a function of the suppressor tone level, enabling the assessment of the threshold and the growth of suppression. Depending on the distance of the suppressor tone to f2, there were marked differences in the suppression behavior of different suppressor frequencies. The threshold of suppression was minimal slightly above f2 and hardly increased with increasing frequency, but increased continuously with decreasing suppressor frequency. The growth of suppression, however, did not systematically change below f2, but decreased rapidly above f2. Both changes resulted in asymmetrical, V-shaped suppression tuning curves. They were sharply tuned to a frequency slightly above f2, with Q10 dB values up to 7.87. This is consistent with the assumption that the main source of the DPOAE is at the f2 site. In some cases, the DPOAE was particularly sensitive to suppressor tones near the DPOAE frequency. In one individual case, facilitation was found for corresponding frequency-level ranges of the suppressor tone. This may suggest a secondary emission source at the distortion product place.
Recognition of amplitude-modulation patterns in the presence of a distractor. I. Effects of correlation and frequency relation
Authors: Takeuchi Annie H. , Braida Louis D.
Published: October 2005

Listeners’ ability to compare the amplitude modulation pattern of 200- and 500-Hz targets when distractors that were also amplitude modulated were presented simultaneously was evaluated. The amplitude modulations of the distractors were either uncorrelated, partially correlated, or fully correlated with the amplitude modulations of the comparisons. Relative to the case of no distractor, performance tended to decrease when a distractor was present, and the degree of interference increased as the modulation correlation between the comparisons and distractors decreased. Although the interference was greater when the comparisons and distractors were separated by 50 Hz, there was also significant interference when the separation was 300 Hz. Whether the comparison was higher or lower in frequency than the distractor had no overall effect. However, the effect of modulation correlation was greater when comparisons were higher than distractors rather than lower. Patterns of interference are compared to those found in studies of modulation detection and discrimination interference, and implications for the use of multiple-band signals that carry the amplitude envelopes from different spectral regions of a speech signal to convey speech are discussed.
Cross-frequency interactions in the precedence effect
Authors: Shinn-Cunningham B. G. , Zurek P. M. , Durlach N. I. , Clifton R. K.
Published: October 2005

This paper concerns the extent to which the precedence effect is observed when leading and lagging sounds occupy different spectral regions. Subjects, listening under headphones, were asked to match the intracranial lateral position of an acoustic pointer to that of a test stimulus composed of two binaural noise bursts with asynchronous onsets, parametrically varied frequency content, and different interaural delays. The precedence effect was measured by the degree to which the interaural delay of the matching pointer was independent of the interaural delay of the lagging noise burst in the test stimulus. The results, like those of Blauert and Divenyi [Acustica 66, 267–274 (1988)], show an asymmetric frequency effect in which the lateralization influence of a lagging high-frequency burst is almost completely suppressed by a leading low-frequency burst, whereas a lagging low-frequency burst is weighted equally with a leading high-frequency burst. This asymmetry is shown to be the result of an inherent low-frequency dominance that is seen even with simultaneous bursts. When this dominance is removed (by attenuating the low-frequency burst) the precedence effect operates with roughly equal strength both upward and downward in frequency. Within the scope of the current study (with lateralization achieved through the use of interaural time differences alone, stimuli from only two frequency bands, and only three subjects performing in all experiments), these results suggest that the precedence effect arises from a fairly central processing stage in which information is combined across frequency.
Behavioral auditory thresholds for sinusoidal electrical stimuli in the cat
Authors: Smith David W. , Watt Susan , Konrad Karl E. M. , Olszyk Valerie B.
Published: October 2005

Behavioral thresholds were measured in four cats by training them to respond behaviorally to acoustic auditory stimuli using food as a reward in an operant reinforcement paradigm. Following training, the subjects were implanted unilaterally with either a scaled-UCSF electrode containing four contacts or an electrode array containing eight intracochlear contacts and one extracochlear contact under temporalis muscle. Behavioral thresholds for electrical stimuli were obtained as a function of sinusoidal frequency, duration, and electrode configuration. Threshold functions for both electrode types and all animals had minima between 48 and 125 Hz and, in general, were relatively flat below this minima; functions increased at 3–6 dB/octave from 96 Hz to 1 kHz. Threshold varied predictably as a function of electrode configuration, with thresholds decreasing as much as 20 dB as electrode spacing was widened from a radial bipolar (200-μm separation) to a monopolar configuration (apical stimulating and temporalis return). With long-duration stimuli, increasing the electrode separation systematically increased the slope of the threshold-versus-frequency contours in all animals. Irrespective of electrode type or configuration, charge/phase thresholds for single-cycle sinusoids were relatively flat for stimulus periods up to 1–5 ms, approximating a constant charge/phase determination of threshold. At phase durations greater than 5 ms, charge thresholds increased at a rate slightly above 6 dB/octave (constant peak current), which was suggestive of neural accommodation. Thresholds for the cat share many features with those reported for implanted humans and monkeys.
Application of the fast Fourier transform to broadband beamforming
Authors: Godara Lal C.
Published: October 2005

The processing of broadband signals using an array of sensors is normally carried out in a time domain using a tapped delay line filter or in a frequency domain where each frequency channel is weighed by complex weights and no tapped delay line filter is required. The time domain implementation of the broadband structure is important in the area of communication where the frequency domain implementation may not be suitable due to its associated delay. This paper derives relationships between the weights, the array correlation matrices, and the constraints on the weights of the two structures to produce identical results. These relationships are then used to update the weights of the tapped delay line filter structure using narrow-band techniques. The method has potential for computational saving to estimate weights of the broadband structure, for a large bandwidth signal requiring a long tapped delay line filter.
Digital frequency-domain implementation of optimum broadband arrays
Authors: Liu Chen , Sideman Samuel
Published: October 2005

The problem considered is that of implementing the optimum broadband arrays whose weights are functions of frequency that have been derived based on a certain performance criterion. The sensor signals are decomposed with a fast Fourier transform (FFT) filterbank so that each frequency component may be faithfully beamformed with these optimal weights. A method of time interpolation by padding zeros in the frequency domain is developed for a high precision phase delay, without increasing the sensor channel sampling rate. An input and output pruned decimation-in-frequency FFT algorithm is also developed for an efficient practical computation procedure. Error factors affecting the accuracy of this technique are specified and suggestions concerning reduction of these errors are given.
A hybrid method for predicting the complete scattering function from limited data
Authors: Schenck Harry A. , Benthien George W. , Barach Don
Published: October 2005

The three-dimensional acoustic scattering function of an object is very difficult and expensive to measure, even in controlled experiments. Usually one is limited to sampling this function at a limited number of monostatic angles and perhaps at a few bistatic angles in a single plane. However, the three-dimensional function is controlled by relatively few degrees of freedom at low frequencies. By using a computational model to generate the far-field propagator function for the object, and applying reciprocity conditions as a constraint, a least-squares problem can be formulated to estimate the radiating part of the surface source strength. Singular value decomposition of the propagator function is used to identify the efficient radiating modes. Once the surface source density is determined by solving the least-squares problem, the full three-dimensional scattering function can be reconstructed. The theoretical basis for this technique will be presented, along with a discussion of results obtained to date. Practical issues dealing with the numerical implementation and computational efficiency will also be discussed.