bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimum audible movement angle in the horizontal plane as a function of stimulus frequency and bandwidth, source azimuth, and velocity
Authors: Chandler David W. , Grantham D. Wesley
Published: October 2005

Minimum audible movement angles (MAMAs) were measured in the horizontal plane for four normal-hearing adult subjects in a darkened anechoic chamber. On each trial, a single stimulus was presented, and the subject had to say whether it came from a stationary loudspeaker or from a loudspeaker that was moving at a constant angular velocity around him. Thresholds were established by adaptively varying stimulus duration. In experiment 1, MAMAs were measured as a function of center frequency (500–5000 Hz), velocity (10°–180°/s), and direction of motion (left versus right). There was no effect of direction of motion. MAMAs increased with velocity, from an average of 8.8° of arc for a target moving at 10°/s to an average of 20.2° of arc for a target moving at 180°/s. MAMAs were higher for a 3000-Hz tone than for tones of lower or higher frequencies, as has been previously reported [D. R. Perrott and J. Tucker, J. Acoust. Soc. Am. 83, 1522–1527 (1988)]. In experiment 2, minimum audible angles (MAAs) were measured with sequentially presented stationary tone pulses (500–5000 Hz), and were shown to exhibit the same dependence on signal frequency that the MAMAs showed (average MAA at 3000 Hz: 8.4°; average MAA at the other frequencies: 3.4°).

In experiment 3, MAMAs and MAAs were measured as a function of stimulus bandwidth (centered at 3000 Hz) and listening azimuth (0° vs 60°). Average MAAs decreased monotonically as stimulus bandwidth increased from 0 Hz to wideband (from 8.4° to 1.2° at 0° azimuth; from 11.3° to 1.5° at 60° azimuth). As in experiment 1, MAMAs increased with stimulus velocity, from values comparable to the MAAs for the slowest-velocity (10°/s) targets to 70° of arc or more in the poorest condition (third-octave band of noise presented at a velocity of 180°/s and an azimuth of 60°). MAMAs obtained in the slower-velocity conditions depended in the same way on stimulus bandwidth and listening azimuth that MAAs depended on these variables. In no case was the MAMA ever smaller than the MAA. It is hypothesized that a minimum integration time is required to achieve optimal performance in a dynamic spatial resolution task. Average estimates of this minimum time based on the current data vary from 336 ms (for targets presented at midline) to 1116 ms (for narrow-band targets presented at 60° azimuth). The relatively large magnitudes of these minimum integration times are consistent with the view of the binaural processor as a sluggish system.
The dominant role of low-frequency interaural time differences in sound localization
Authors: Wightman Frederic L. , Kistler Doris J.
Published: October 2005

Two experiments are described in which listeners judge the apparent directions of virtual sound sources–headphone-presented sounds that are processed in order to simulate free-field sounds. Previous results suggest that when the cues to sound direction are preserved by the simulation, the apparent directions of virtual sources are nearly the same as the apparent directions of real free-field sources. In the experiments reported here, the interaural phase relations in the processing algorithms are manipulated in order to produce stimuli in which the interaural time difference cues signal one direction and interaural intensity and pinna cues signal another direction. The apparent directions of these conflicting cue stimuli almost always follow the interaural time cue, as long as the wideband stimuli include low frequencies. With low frequencies removed from the stimuli, the dominance of interaural time difference disappears, and apparent direction is determined primarily by interaural intensity difference and pinna cues.
Effectiveness of earplugs in high-intensity impulse noise
Authors: Dancer Armand , Grateau Paul , Cabanis Alex , Barnabé Gilles , Cagnin Gilles , Vaillant Thierry , Lafont Denis
Published: October 2005

The efficiency of different types of earplugs was assessed by means of Békésy audiometry following the exposure of 42 human subjects to weapon impulses. The peak pressure of the impulses ranged from 2.3–27.8 kPa (from 161 to 183-dB peak SPL) and the A-weighted equivalent level (over 8 h) of each exposure ranged from 100–114 dB. All subjects wore earplugs fitted by an experienced individual. The devices tested included one brand of conventional foam earplugs and a number of different models of perforated earplugs, one type of which had been previously shown to provide nonlinear attenuation. Perforated earplugs were tested because they provide better speech communication than conventional passive earplugs, and in the nonlinear case also afford attenuation that increases with the peak pressure of the impulses. The temporary threshold shifts (TTSs) observed in these experiments were very small and indicated no significant hazard for hearing. Well-fitted perforated earplugs seem to be able to protect the ear from infrequent exposures to the high-level impulses produced by small and large weapons while allowing good speech communication, and without impairing the operational capacity of soldiers who must remain aware of their acoustic environment.
Segmental durations in the vicinity of prosodic phrase boundaries
Authors: Wightman Colin W. , Shattuck-Hufnagel Stefanie , Ostendorf Mari , Price Patti J.
Published: October 2005

Numerous studies have indicated that prosodic phrase boundaries may be marked by a variety of acoustic phenomena including segmental lengthening. It has not been established, however, whether this lengthening is restricted to the immediate vicinity of the boundary, or if it extends over some larger region. In this study, segmental lengthening in the vicinity of prosodic boundaries is examined and found to be restricted to the rhyme of the syllable preceding the boundary. By using a normalized measure of segmental lengthening, and by compensating for differences in speaking rate, it is also shown that at least four distinct types of boundaries can be distinguished on the basis of this lengthening.
Analysis of nasal consonants using perceptual linear prediction
Authors: Qi Yingyong , Fox Robert A.
Published: October 2005

Until recently, speech analysis techniques have been built around the all-pole linear predictive model. This study examines the effectiveness of using the perceptual linear predictive method for analyzing nasal consonants. Six speakers (three men and three women) produced 300 CV syllables with initial nasal consonants /m/ and /n/. A threshold-based boundary detection algorithm was developed to extract nasal segments from the CV contexts. Poles of a fifth-order perceptual linear predictive model were calculated and the frequency of the second pole was used to characterize the place of articulation of nasal consonants. Results indicated that the frequency for the second transformed pole was significantly lower for /m/ than for /n/ and was independent of factors such as vowel context and gender of the speaker. A nasal identification rate of 86% was obtained based on the frequency of the second pole. The use of the perceptual linear predictive method may thus overcome some difficulties associated with analyzing nasal consonants.
Comparison of sonic boom rise time prediction techniques
Authors: Bass Henry E. , Raspet Richard
Published: October 2005

An important quantity in determining the loudness of sonic booms outdoors is the rise time. In the absence of turbulence, the rise time is dictated by frequency-dependent loss mechanisms in the atmosphere including relaxation, viscosity, and thermal conduction. Two techniques have been used to predict rise times of sonic booms. The technique developed by Pestorius and Blackstock numerically steps a weak shock through the atmosphere accounting for frequency-dependent absorption and time-dependent wave steepening independently at each step. This technique has been extended by Bass and Raspet to include absorption and dispersion by the vibrational relaxation of N2 and O2 in the presence of H2O. The second technique is to apply the augmented Burgers’ equation to determine a steady-state asymptotic shock profile. This approach is strictly valid only for a plane shock wave with a duration much greater than the rise time. This letter compares predicted rise times using these two approaches. The input waveforms were assumed to be N waves with a linear rise at the front and rear of the shock. These calculations show that N waves of duration greater than 100 times the rise time can be treated as steady-state shocks. The rise time for shock waves of shorter duration cannot be determined using the steady shock assumption.
A polynomial fit for calculating the electromechanical coupling constants of piezoelectric materials using the method described by Onoe e
t a
l. [J. Acoust. Soc. Am. 3
5, 36–42 (1963)]
Authors: Sherrit Stewart , Wiederick Harvey D. , Mukherjee Binu K.
Published: October 2005

The usual methods for determining the electromechanical coupling constants of piezoelectric materials are described in the IEEE standard on piezoelectricity (IEEE Standard on Piezoelectricity 176-1987). When spurious resonances are present, the standard recommends the use of a method that involves the use of a numerical table of corresponding values. In order to allow for atuomation of this method, a polynomial function that gives a good fit to the numerical table has been found.
Normal mode solution for low-frequency sound propagation in a downward refracting atmosphere above a complex impedance plane
Authors: Raspet Richard , Baird Gordon , Wu Wenliang
Published: October 2005

The development of the fast field and parabolic equation solutions to the wave equation has made it possible to solve for the combined effects of refraction in a layered atmosphere and the interaction of sound with a complex impedance ground surface. In many respects the numerical methods have advanced beyond our understanding of the basic phenomena. In an earlier study [J. Acoust. Soc. Am. 89, 107–114 (1991)], the residue series solution for upward refraction was investigated and provided insight into the nature of the interaction of refraction and ground reflection. In this paper results are presented of a similar normal mode solution for downward refraction above a complex impedance ground surface. This model is used to investigate when the surface wave is excited for downward refraction conditions and to develop criteria for the maximum range of cylindrical decay as a function of phase and magnitude of the ground impedance and the magnitude of the sound velocity gradient.
Very low frequency ambient noise at the seafloor under the Beaufort Sea icecap
Authors: Webb Spahr C. , Schultz Adam
Published: October 2005

The first results from a deployment of four instruments on the floor of the Beaufort Sea in March 1990 are presented. The instruments recorded pressure fluctuations in the band from 0.0005 to 8 Hz during a 2-week period. The pressure spectra derived from these measurements show very low energy in the microseism peak near 0.1 Hz in comparison with measurements from the Pacific or Atlantic seafloor. The microseism band shows a series of spectral peaks and valleys likely associated with the modes of the ocean–seafloor Rayleigh wave waveguide. The shape of the microseism peak is remarkably stable during the experiment although the amplitude varies by about 10 dB. The signals are very coherent between adjacent instruments and suggest propagation in the microseism band from a source in the Gulf of Alaska. The pressure spectra rise rapidly toward lower frequency below 0.02 Hz, but Arctic spectra are less energetic than spectra from sites on either Pacific or Atlantic seafloors at all frequencies. The long period energy appears to be related to flexural-gravity waves on the ocean surface. The pressure measurements predict amplitudes for these waves in general agreement with previous tilt and displacement measurements made on the ice.
Tomographic imaging of opaque and low-contrast objects in range-independent waveguides
Authors: Carrion Philip , Boehm Gualtiero
Published: October 2005

A feasibility study is presented for acoustic tomographic imaging of arbitrarily shaped objects in range-independent oceanic waveguides. One of the main obstacles in the efficient use of tomographic imaging is that tomographic systems usually allow for a number of different independent solutions which satisfy the same systems of equations. This adverse property of acoustic tomography is especially pronounced in underdetermined systems characterized by null spaces of tomographic matrices which relate measured data to an unknown sound-speed distribution. In fact, acoustic tomography is usually underdetermined and the null space problem becomes critical in many applications. Acoustic tomography in many instances yields blurred images precluding its efficient use for mapping underwater objects in oceanic waveguides. How to improve the resolving power of tomographic imagery in waveguides is shown. A new technique based on the sliding window approach is suggested which uses constrained traveltime inversion. The method will be tested on mapping opaque and low-contrast acoustic objects placed in range-independent waveguides. The method is fast since it does not directly invert tomographic matrices of large rank but instead carries out summation over nonzero elements of tomographic matrices. It can be proved that constrained inversion compensates for limited angular aperture recording and thus can be applied to practical problems with incomplete angular aperture. This work is limited to processing of transmitted signals. A separate study will be devoted to the analysis of reflection data.
Matched-field processing enhancement in a shallow-water environment by incoherent broadband averaging
Authors: Smith G. B. , Feuillade C. , DelBalzo D. R.
Published: October 2005

Incoherent broadband averaging is a method that uses the broadband nature of an acoustic source to acquire additional gain against ambient noise and to decrease background variance common to matched-field ambiguity surfaces. In this paper, the relationship between the performance of incoherent broadband averaging and averaging parameters (i.e., bandwidth and the number of ambiguity surfaces averaged) is explored, and general guidelines for choosing these parameters are described. Expressions relating environmental parameters to the width and spacing of the sidelobes are obtained. These expressions predict the minimum bandwidth needed for incoherent broadband averaging for the case where one sidelobe dominates. Computer simulations in a Pekeris waveguide using a simulated but realistic noise field are used to verify the theoretical results. The simulations confirm the existence of the minimum bandwidth below which no effective averaging occurs. If the bandwidth equals or exceeds the minimum bandwidth, measures of peak-to-background resolution expressed in units of the variance improve by 5 log(L), where L is the number of surfaces included in the average.
Radiation of sound into a cylindrical enclosure from a point-driven end plate with general boundary conditions
Authors: Cheng Li , Nicolas Jean
Published: October 2005

The radiation of sound from a point-driven circular plate into a hard-walled cylindrical enclosure is investigated. Emphasis is given on studying the effects of the boundary conditions of the plate, which are modeled as a continuous distribution of edge springs acting against both the deflection and the rotation of the contour of the plate. With this model, both classical and intermediate boundary cases can be simulated by adjusting the elastic stiffness of the springs. A coupled acoustoelastic formulation is developed following a variational approach, with the use of hard-walled cavity modes. In the analysis, the full interaction between the structure vibration and the internal cavity sound pressure is considered. Numerical results indicate that a significant reduction in noise inside the cavity can be obtained for a relatively wide frequency range by completely relaxing the translational support (zero deflection stiffness) of the plate. This is mainly due to a weakening of the modal radiation efficiency of the flexural modes of the plate. With an increase of the deflection stiffness on the contour of the plate, this beneficial frequency range is shifted to higher frequencies. It is hoped that the findings of the present work will be useful for practical predictions of airplane cabin noise emitted by the rear pressure bulkhead, as well as for noise control in some aerospace structures and mechanical systems involving cylindrical-shaped cavities.
Predicting theater chair absorption from reverberation chamber measurements
Authors: Bradley J. S.
Published: October 2005

The sound absorption of small samples consisting of up to 18 upholstered theater chairs was measured in a reverberation chamber and these results were related to the effect of larger samples of the same chairs in auditoria. The sound absorption coefficients of the chairs, measured in a reverberation chamber, were found to be linearly related to the ratios of perimeter to area of the samples of chairs. Extrapolating these reverberation chamber measurements to smaller perimeter to area ratios, characteristic of seating blocks in auditoria, produced good agreement with measurements of the same seats in the auditoria. This procedure is proposed as a more accurate approach to predicting the absorbing characteristics of upholstered theater chairs in auditoria. Three other more approximate approaches were also considered including the use of screens to eliminate edge absorption, average sample size corrections, and the use of average absorption coefficients for all types of chairs. The merits of each approach are discussed and data are given for average sample size corrections.
Joint modeling and maximum-likelihood estimation of pitch and linear prediction coefficient parameters
Authors: Burshtein David
Published: October 2005

The well-known speech production model is considered, where the speech signal is modeled as the output of an all-pole filter driven either by some white noise sequence (unvoiced speech) or by the sum of a periodic excitation and a noise sequence (voiced speech). Approximate maximum-likelihood (ML) estimation algorithms for the unvoiced case are well known. The ML estimator of the parameters is obtained for the voiced speech model. These parameters consist of the parameters of the periodic excitation (pitch parameters) and the parameters of the filter [linear prediction coefficient (LPC) parameters]. The results of the application of the algorithm on simulated and on real speech data are presented.
IRP (interference rejection processor) revisited—A new approach to multiple-interference rejection and elimination of beam pattern distortion
Authors: Minkoff J.
Published: October 2005

An algorithm is presented that enables rejection of an arbitrary number of interfering sources at an array with no distortion or sidelobe degradation of the array beam pattern. The algorithm is an extension of the earlier interference rejection processor (IRP) algorithm, which is a well-known method for rejecting single-interference sources. Rejection of two interfering sources by ∼40 to 50 dB with no beam pattern distortion is demonstrated in a computer experiment using simulated data.
Critical behavior of the ultrasonic attenuation and velocity and shear viscosity for the binary mixture of carbon tetrachloride and coconut oil
Authors: Abdelraziq Issam R. , Yun S. S. , Stumpf F. B.
Published: October 2005

Measurements of the ultrasonic velocity and absorption at the critical concentration were made as a function of temperature and frequency for the binary mixture of carbon tetrachloride and coconut oil. In addition, viscosity measurements were made. Ultrasonic absorption at 5, 7, 10, 15, 21, 25, 30, and 35 MHz above Tc is analyzed by the dynamic scaling theory of Ferrell and Bhattacharjee [Phys. Rev. A 31, 1788 (1985)]. The values of αc/f2 vs f−1.06 show a good agreement with the theory. Also, the experimental values of α/αc for carbon tetrachloride and coconut oil are compared to the scaling function F(ω*). The temperature and frequency dependence of the velocity are also determined. The coefficient of viscosity of the critical mixture shows a different temperature dependence from that of the pure components.
The propagation of Lamb waves in a plate bordered with layers of a liquid
Authors: Wu Junru , Zhu Zhemin
Published: October 2005

The influence of liquid layers on the propagation of Lamb waves in a plate of finite thickness is studied theoretically. The dispersion equations of Lamb waves in a plate bordered with layers of liquids are derived. Numerical solutions of the equations show that the phase velocity of Lamb waves changes with the thickness of the liquid layers. For the lowest antisymmetrical mode of very thin plates, the numerical results calculated from the dispersion equations are compared with those derived from the bending wave acoustic impedance approach. The limitation of the latter is discussed. Applications of Lamb waves pertinent to biosensing are also presented.
Transient response of thick circular and square bars subjected to transverse elastic impact
Authors: Lin Yiching , Sansalone Mary
Published: October 2005

The objective of the studies presented in this paper was to understand the transient response of thick circular and square bars subjected to transverse elastic point impact. It is shown that the transient response is composed of a number of resonant frequencies caused by cross-sectional modes of vibration. The individual cross-sectional modes and their corresponding natural frequencies were determined using plane strain and three-dimensional finite-element models of circular and square cross sections. The first few modes for both circular and square cross sections are shown. Subsequently, three-dimensional finite-element models of circular and square bars were used to determine the transient response caused by transverse point impact. To verify the results obtained from the numerical models, experimental studies were performed on a 0.4-m-diam circular bar and a 0.3-m square bar. These specimens were representative of full-size concrete columns—typical barlike structural elements. The results of these experimental studies were in excellent agreement with those obtained from the finite-element analyses. A future paper will present the results obtained from numerical and experimental studies on rectangular bars.
Frequency-flow speed dependence of structural response to turbulent boundary layer pressure excitation
Authors: Rumerman M. L.
Published: October 2005

A rectangular simply supported plate is used to illustrate the differing dependencies on center frequency and flow speed of the spatially averaged one-third-octave band mean squared acceleration levels of a structure due to different mechanisms of response to turbulent boundary layer (TBL) excitation. The two mechanisms described are direct excitation of resonant modes by the TBL components in the neighborhood of the wave numbers of the resonant modes, and the coupling into the resonant modes of those TBL components in the neighborhood of the TBL convective peak. Estimates of the mean-squared response are made for different representations of the TBL wave-number-frequency spectrum. When determination of the dominant response mechanism is important, it appears that it can be made by performing a regression analysis on measured results and comparing the derived parameters to the alternative theoretical estimates.
Sound scattering from an internally loaded cylindrical shell
Authors: Guo Y. P.
Published: October 2005

Sound scattering from a cylindrical shell with a mass-spring system diametrically attached inside it is examined analytically. Explicit solutions for both the shell motions and the scattered acoustic field are derived. It is shown that the attachment of the simple mass-spring loading causes significant changes in the acoustic behavior of the shell. The scattering from the internally loaded shell is shown to be dominated by the interactions between structural waves in the shell and the attachment, which have an overall resonant effect, manifested by a series of scalloplike variations in the scattering form function in the low- and intermediate-frequency domain. In the low-frequency region, it is shown that in contrast to the case of an empty shell where scattering is essentially controlled by the total mass of the scatterer, the acoustic behavior of the internally loaded shell is basically determined by waves in the shell, and, hence, is elasticity controlled. It is found that the shell deformation is dominated by short-wavelength structural waves. This is shown to be the case even for very long-wavelength incident sound. In the high-frequency region, the two subsystems are essentially decoupled from each other in this mass-spring model, because the coupling forces (or impedances) reduce rapidly to zero and become out of phase with the shell velocities at the attachment points as frequency increases. Effects of dissipation in both the internal system and the shell are examined, which shows that the scattering is largely unaffected by dissipation in the internal system. However, damping in the shell dissipates the structural waves, and, hence, affects the scattering that is dominated by the interactions of these waves with the loading.
The forced response of an acoustic-structural coupled system
Authors: Pan Jie
Published: October 2005

The sound-pressure response of an acoustic-structural coupled system to both air-borne and structure-borne excitations has been studied. Both steady-state and transient-state sound field responses of the system can be characterized by the system modal behaviors and by the nature of the driving forces. This paper presents a method to describe the sound and vibration fields of the coupled system in terms of modal coupling analysis. In particular, analytical expressions for steady-state and transient-state sound-pressure fields in a panel–cavity coupled system are obtained. They are used to calculate the frequency response and transient decay of the sound field in the cavity. The effect of the system eigenvalue distributions (or the pole locations in the sound field transfer functions) upon the sound field response is demonstrated by numerical examples.
Quality of underwater source localization in a multipath environment
Authors: Daku Brian L. F. , Salt J. Eric , McIntyre C. Mark
Published: October 2005

This paper investigates the accuracy of a passive underwater localization system using two submerged omnidirectional sensors in a multipath environment. Expressions for the variance and bias of localization error are developed for two sources of error: ocean noise and sensor perturbations. Expressions are also given for the variance of time delays obtained from the cross correlation of the two sensor signals. It is shown that the variance of localization error is very sensitive to vertical sensor perturbations. It is also shown that in the region where the time difference of arrival (TDOA) of the surface reflected paths is approximately equal to the TDOA of the direct paths, the localization error is very large.
Forward modeling and data inversion for beam propagation in a stratified medium. I: Theory
Authors: Lu I-Tai
Published: October 2005

A previously developed matrix Green’s function formulation [I. T. Lu and L. B. Felsen, Geophys. J. R. Astron. Soc. 84, 31–42 (1986)] for line-source excited propagation in piecewise-homogeneous stratified media is extended to allow arbitrarily inhomogeneous layers and beam source excitation. This formulation reveals dominant wave processes and allows simultaneous excitation and detection at arbitrarily specified locations. It provides a unified and systematic approach for deriving all alternative representations including mode, ray(beam), spectral integral, ray(beam) mode, collective ray(beam), etc. Both rigorous and practical aspects of the analytic continuation procedures in the complex source point technique are discussed in detail. An efficient beam source localization algorithm, which estimates the beam parameters and the beam location sequentially, is also presented. Numerical results are presented in a companion paper [I. T. Lu and H. Y. Chen, J. Acoust. Soc. Am. 91, ▪▪▪–▪▪▪ (1992)].
Forward modeling and data inversion for beam propagation in a stratified medium. II: Numerical results
Authors: Lu I-Tai , Chen Han-Yang
Published: October 2005

The general theory of both forward and inverse modelings for beam propagation in stratified media developed in Part I of this presentation [I-Tai Lu, J. Acoust. Soc. Am. 91, ▪▪▪▪–▪▪▪▪ (1992)] is examined in detail by numerical simulations. Modes, collective beams, and conventional beams have been employed to calculate the beam-excited wave phenomena in both piecewise-homogeneous and arbitrarily inhomogeneous layered media. These algorithms are formulated in the same framework and yield essentially the same results. Efficient data inversion procedures to minimize least-square errors for localizing a beam source are also presented and examined by numerical simulations. The conventional modal-filtering procedure using inner products of the received signals with the orthonormal eigenfunctions is proved to be a special case of a weighted least-square scheme.
Effects of dispersion on the inference of metal texture from S plate mode measurements. Part I. Evaluation of dispersion correction methods
Authors: Li Yan , Thompson R. Bruce
Published: October 2005

Ultrasonic S0 waves (fundamental symmetric Lamb modes) are being considered in several laboratories for the nondestructive characterization of the texture (preferred grain orientation) and formability of metal sheets and plates. In a typical experimental setup, the velocities of the S0 waves are measured as a function of wave propagation angle with respect to the rolling direction of the plate. However, the S0 waves are known to be dispersive, and that dispersion must be considered in order to isolate the small, texture-induced shifts in the S0 wave velocity. Currently, there are two approximate dispersion correction methods, one proposed by Thompson et al.9 and the other introduced by Hirao and Fukuoka.20 In this paper, these two methods will be evaluated using an exact theory for wave propagation in orthotropic plates. Through the evaluation, the limits of the current texture measurement techniques are established. It is found that when plate thickness to wavelength ratio is less than 0.15, both Thompson’s and Hirao’s methods work satisfactorily. When the thickness to wavelength ratio exceeds 0.3, neither Thompson’s nor Hirao’s dispersion correction method provides adequate corrections for the current texture measurement techniques. Within the range of 0.15–0.3, Thompson’s method is recommended for weakly anisotropic sheets and plates and Hirao’s method may be more appropriate for some strongly anisotropic cases.
A formulation of multiple scattering by many bounded obstacles using a multicentered, T supermatrix
Authors: Lim Raymond , Hackman Roger H.
Published: October 2005

The acoustic scattering from many interacting, bounded, three-dimensional obstacles has been treated by several authors [see, for example, V. Twersky, J. Math. Phys. 8, 589 (1967) or B. Peterson and S. Ström, J. Acoust. Soc. Am. 56, 771 (1974)]. In particular, Peterson and Ström extended the single-obstacle, transition (T) matrix formalism to several obstacles (including all orders of multiple scattering) by using the translation properties of the spherical basis functions to translate the multiply scattered fields of each obstacle to a common origin. Later, their formalism was extended to treat elastic wave scattering by using spherical vector basis functions [A. Boström, J. Acoust. Soc. Am. 67, 399 (1980)]. However, for numerical results, the present state of development is cumbersome to apply to more than two obstacles and convergence of the rescattering matrices is sensitive to obstacle separation. In this paper, a multicentered, T-matrix formalism for acoustic and elastic wave scattering is given, based on field expansions centered on each obstacle. Like previous approaches, it also incorporates the single-obstacle T matrix and sums the multiple scattering series exactly. The result is simpler and less numerically sensitive to the separation of the obstacles. The extension of the formalism to treat the scattering from infinite systems that periodically repeat an arbitrary group of obstacles is also given. Numerical calculations based on the exact formalism for scattering from a linear array of as many as ten spherical obstacles are presented. The validity of approximating the scattered field from larger finite arrays by the field scattered from finite sections of an infinite array is considered.
Numerical solution of the direct scattering problem through the transformed acoustical wave equation
Authors: Pourjavid Sussan , Tretiak Oleh John
Published: October 2005

A transformation is applied to the acoustical wave equation to obtain a new equivalent form that does not contain gradients of the pressure. A new technique, based on the spectral method, is developed for the numerical solution of the direct time domain scattering problem. Modeling techniques for obtaining accurate solutions are discussed and numerical examples are presented.
Computation of the far-field time domain solution of the scattering problem
Authors: Pourjavid Sussan , Tretiak Oleh John
Published: October 2005

This paper presents a new technique for calculating the time domain (transient) far-field scattered pressure. The scattering problem is divided in two steps; the first step evaluates the field distribution inside the scatterer, and the second step generates the far-field scattered pressure by 3-D Radon transform of these data for each time step and summing over time. The algorithm results in considerable saving in CPU time and memory by simplifying the calculation along the path from scatterer to receiver. This technique can also be used in two dimensions.
Acoustic scattering from arbitrarily shaped multiple bodies in half-space: Method of moments solution
Authors: Rao Sadasiva M. , Sridhara B. S.
Published: October 2005

In this work, the method of moments solution is applied to calculate the scattered or radiated fields from arbitrarily shaped, multiple rigid bodies located in an infinite half-space. Both cases, that is, when the bodies are away from the infinite plane and when the bodies are situated in contact with the infinite plane, have been treated. It is noted that no special treatment was required when the bodies are in actual contact with the infinite plane. The numerical technique presented in this work is simple, efficient, and accurate. Numerical results are presented for certain canonical shapes and compared with alternate formulations.
Acoustic wave propagation in a cylindrical borehole with fractures
Authors: Spring C. T. , Dudley D. G.
Published: October 2005

The problem of acoustic wave propagation in a cylindrical borehole possessing a finite number of transverse discontinuities is studied. The field behavior is modeled through Green’s function techniques and an integral equation is formulated to solve for the acoustic field everywhere within the structure. Asymptotic forms are investigated to speed the numerical convergence of our solution. To solve the integral equation both the method of moments and a low-frequency approximation are employed. The reflection coefficient in the time and frequency domains is studied. After presenting solutions for the one and two fracture case, the analysis is generalized for many fractures.
Propagation of sound and the assignment of shape factors in model porous materials having simple pore geometries
Authors: Stinson Michael R. , Champoux Yvan
Published: October 2005

The acoustical properties of a class of simple porous materials have been studied experimentally and theoretically. Rigid-frame materials containing air-filled pores of uniform cross section were investigated. Two model porous materials were constructed, one with pores of rectangular cross section (0.0146×0.0172 cm) and one with pores of triangular cross section (0.037-cm sides). The characteristic impedance and propagation constant were measured for frequencies between 50 and 4500 Hz and good agreement with exact theoretical predictions was obtained. The exact theoretical expressions for specific pore shapes (e.g., slitlike, square, and triangular) can be used to investigate the assignment of shape factors by various general but approximate theoretical models. It is demonstrated that the model introduced by Attenborough requires a shape factor that is frequency dependent. A theoretical model, appropriate for materials containing pores of uniform cross section, that correctly treats the low- and high-frequency behavior, is presented. Given subsidiary measurements of flow resistivity, porosity, and tortuosity, a single shape factor leads to very good agreement with the exact solutions for all frequencies.
Nonlinear pressure fields due to focused circular apertures
Authors: Baker Andrew C.
Published: October 2005

The use of high amplitude focused ultrasound fields is widespread in medical diagnosis and therapy but there has been relatively little work published that compares experimental measurements with appropriate theory for such systems. In this paper, comparisons are made between the measured continuous-wave pressure field of a focused circular aperture operating at 2.25 MHz and a numerical solution of the nonlinear parabolic wave equation. The measurements were made in water using a 38-mm diam plane circular transducer as the acoustic source with perspex lenses providing focusing, focal lengths of 440, 216, and 142 mm were examined. Results are presented for the amplitudes of the fundamental, second, and third harmonics along and across the acoustic axis of the source. In general, the agreement between experiment and theory is good.
Anderson localization of one-dimensional wave propagation on a fluid-loaded plate
Authors: Photiadis Douglas M.
Published: October 2005

The propagation of flexural waves along a fluid-loaded plate with an irregular array of line attachments is examined. The system is shown to be equivalent to a one-dimensional chain with a nearest neighbor coupling arising from the fluid-loaded wave, and a long-range coupling due to bulk waves in the fluid. The magnitude of the long-range coupling is shown to be small compared to the nearest neighbor coupling for many applications. The irregularity will thus produce Anderson localization, at least for moderate distances. The equations of motion are numerically solved for two cases: (1) a sparse array for which the long-range coupling is expected to be negligible, and (2) a dense array for which the long-range coupling is fairly small, but not negligible. Unambiguous Anderson localization effects were observed in both cases.
Piezocomposite coating for active underwater sound reduction
Authors: Howarth Thomas R. , Varadan Vijay K. , Bao Xiaoqi , Varadan Vasundara V.
Published: October 2005

An active acoustic coating is presented for layering over objects in a fluid medium. The design of the active coating prevents an incident sound wave from reflecting off the acoustic boundary of a submerged object. The acoustic energy associated with the incident disturbance is absorbed out of the medium through a piezocomposite device in the coating and dissipated by internal electrical means. The components encapsulated inside the elastomer coating are a piezocomposite actuator and piezoelectric polymer sensors. The sensor arrangement detects and separates the acoustic field into a signal in terms of the incident acoustic pressure wave. The signal is manipulated through an electronic network to generate an appropriate driving voltage. This output drives a thickness extensional mode piezocomposite transducer (actuator) with a linear velocity profile over a broad frequency band. The actuator excitation results in a dynamic impedance matching with the incident disturbance such that the coating appears as a nonreflective acoustic surface. An advanced coating design includes an actuator that can be simultaneously driven to reduce the reflected and transmitted sound fields. Experimental results are presented for one-dimensional incident planar acoustic waves propagating in a water filled pulse tube.
Particle column formation in a stationary ultrasonic field
Authors: Whitworth Glenn , Coakley W. T.
Published: October 2005

Acoustic radiation-force theory for noninteracting particles predicts that when a particle suspension is exposed to a stationary ultrasonic field, the particles may become concentrated at half-wavelength intervals. In a plane stationary field, these particle concentrations would have the shape of uniform planar sheets. Gould and Coakley have observed that particles within these sheets often redistribute to form striated columns in the direction of the ultrasonic beam. In this paper, it is shown that particle columns can result from radial nonuniformity of the ultrasonic beam. Theory is presented that describes the equilibrium distribution of particles when subjected to the lowest axially symmetric acoustic mode of a cylindrical waveguide having a pressure-release wall. Particles with higher density and lower compressibility than that of the host medium will form a column along the axis of a wide waveguide but will migrate to the wall of a narrow waveguide. The direction of radial movement for lower density particles is a function of compressibility but not of waveguide diameter. Results of experiments carried out using aqueous polystyrene suspensions in tubes having thin walls and driven at 3 MHz with a transducer designed to excite primarily the lowest axially symmetric mode were consistent with theory.
Neural derivation of sound source location: Resolution of spatial ambiguities in binaural cues
Authors: Brainard Michael S. , Knudsen Eric I. , Esterly Steven D.
Published: October 2005

Cues for sound localization are inherently spatially ambiguous. Nevertheless, most neurons in the barn owl’s optic tectum (superior colliculus) have receptive fields for broadband noise stimuli that are restricted to a single region of space. This study characterizes the spatial ambiguities associated with two important sets of localization cues, interaural level differences (ILDs) and interaural phase differences (IPDs), and describes how information is integrated within and across frequencies to resolve these ambiguities. The auditory receptive fields of neurons in the optic tectum were measured with free-field sounds presented from a movable loudspeaker. In contrast to the single regions typical for broadband receptive fields, receptive fields for tonal stimuli usually included additional discrete regions of space (accessory fields). Based on acoustic measurements of ILD and IPD cues made in the external ear canals, it was shown that accessory fields corresponded to locations from which sound sources produced ILD and IPD values that were approximately the same as those arising from the broadband receptive field. In addition, accessory fields had inhibitory surrounds, corresponding to locations from which sound sources produced substantially different combinations of ILD and IPD values. Where an accessory field for one frequency overlapped with the inhibitory surround of a second frequency, an excitatory response to the first frequency could be reduced or eliminated by addition of the second frequency. Because tonal receptive fields for different frequencies always overlapped in the region of the broadband receptive field but tended not to overlap elsewhere, this integration of excitation and inhibition can account for the restriction of broadband receptive fields to a single region of space.
Auditive and cognitive factors in speech perception by elderly listeners. III. Additional data and final discussion
Authors: van Rooij John C. G. M. , Plomp Reinier
Published: October 2005

In a previous study [van Rooij and Plomp, J. Acoust. Soc. Am. 88, 2611–2624 (1990)], it was found that speech-perception performance in a sample of elderly subjects tested in the laboratory may be largely determined by two statistically independent components: (1) a major component representing the progressive middle- to high-frequency hearing loss with age and (2) a minor component mainly representing a general decrement in cognitive performance. In the present study, a selected subset of tests used in the laboratory study was administered to a group of elderly subjects less likely to participate in laboratory experimentation. The results show that approximately all the systematic variance with respect to speech-perception performance, as tested by speech-reception thresholds (SRTs), can be accounted for by the audiogram alone. The implications of the results of the present study and those of earlier ones [van Rooij, Plomp, and Orlebeke, J. Acoust. Soc. Am. 86, 1294–1309 (1989) and van Rooij and Plomp, J. Acoust. Soc. Am. 88, 2611–2624 (1990)] are critically evaluated. It is concluded that age differences with respect to speech perception are most likely due to differences in auditive factors.
Detection of changes in modulation depth of a target sound in the presence of other modulated sounds
Authors: Moore Brian C. J. , Jorasz Urszula
Published: October 2005

These experiments are concerned with the comodulation masking release (CMR) and modulation discrimination interference (MDI) that can occur when modulated carriers are added to a target modulated sound at frequencies remote from the target frequency. Thresholds were measured for detecting increments or decrements in the modulation index (m) of a 1000-Hz carrier (the target) sinusoidally amplitude modulated (SAM) at a 10-Hz rate, with that carrier presented either alone, or with a variety of added sounds. In experiments 1–3, the target had a standard value of m of 0.5. The added sounds had carrier frequencies of either 550 and 1550 Hz or 230 and 3300 Hz, and they were either unmodulated (m=0) or SAM at a 10-Hz rate (in phase with the target), with m=0.25, 0.5, or 0.75. In experiment 1, the target and added sounds were gated on synchronously for a duration of 1000 ms. The added sounds produced MDI, and the amount of MDI increased progressively with increases in the modulation index of the added sounds. In experiment 2, the added sounds were gated on 500 ms before and gated off 50 ms after the 1000-ms target sound. This reduced the MDI, but substantial amounts of MDI remained, especially for the 550- and 1550-Hz added sounds. In experiment 3, the target and added sounds were gated on synchronously for 1550 ms, and the increment or decrement in m was gated on for 1000 ms after a delay of 500 ms. This generally gave rise to more MDI than was found in experiment 2. In experiment 4, the values of m for the target and added sounds were 0.75/0.75, 0.75/1.0, and 1.0/1.0, respectively. The added sound consisted of carriers at 230, 550, 1550, and 3300 Hz. All of the temporal conditions used in experiments 1–3 were examined. The added sounds produced MDI in some conditions and CMR in others. The largest CMR occurred in conditions where the modulation index for the added sounds was 1.0, and the whole target sound was delayed relative to the onset of the added sound. The results are discussed in terms of the factors influencing MDI and CMR, and in terms of the possible role of perceptual grouping mechanisms.