bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of RANES in predicting noise emitted by ground vehicle components.
Authors: Shalis Edward
Published: October 2005

This paper presents an analysis of the radiated noise estimation software (RANES) being developed by TACOM and BBN. The noise prediction capability of the model will be discussed for several major components of ground vehicles in use in the commercial and military fields. Special emphasis will be placed on the engine and its structural subcomponents, including the cooling fan and exhaust. Measured noise sources will be given and compared to the results obtained from RANES. The future structural acoustics modules to be added to RANES will also be discussed and projected validation of the model will be given.
Effects of turbulence on the beamforming technique operated by a sonar array for source-bearing finding in the ocean.
Authors: Tarng J. H. , Chiang Ching-Tai
Published: October 2005

In this paper, the effects of propagation on beamforming technique operated by a vertical sonar array for determining the source bearing are investigated in a turbulent ocean with inhomogeneous background. The received phase of each array element, which is estimated by using the ray theory, is randomly fluctuated due to sound-speed variations in the ocean. The distorted beam pattern for beamforming, which is caused by the phase synthesized incoherently, and the standard deviation of the source bearing estimated by the Fourier direction finding are evaluated in statistical approaches. It has been found that the perturbed phases broaden the beamwidth of the beam pattern, i.e., degrade the resolution ability of direction finding of the sonar array. It is also discovered that the deviation of the source bearing is varied as the location (bearing) of the stationary point source is changed. A Gaussian distribution of sound-speed fluctuation and a bilinear sound-speed profile are assumed.
On the influence of vorticity in acoustic scattering from cylinders with discontinuous surface impedance.
Authors: Ginsberg Jerry H. , McDaniel J. Gregory
Published: October 2005

The presence of viscosity leads to boundary conditions on tangential, as well as normal, velocity components. If a wave is incident on a surface whose impedance varies discontinuously, ideal fluid theory predicts that the surface velocity also is discontinuous, which leads to the possibility that large shear stresses and an associated vortical velocity component are generated. The present study considers incidence of a temporally harmonic plane wave on an infinite cylinder whose surface is coated by four regions of alternating high and low impedance. A Helmholtz resolution of the particle velocity transforms the Navier–Stokes equations to a lossy Helmholtz equation for the acoustic pressure and a diffusion equation for the vorticity. The general solution for the scattered field is obtained by representing the azimuthal dependence in a Fourier series, whose coefficients are determined by satisfying the boundary conditions. When the surface properties are uniform, orthogonality conditions make it evident that the vortical effect is only significant in a very thin boundary layer. The discontinuous impedance case is solved by a collocation method. Although the corresponding equations suggest that viscosity might become increasingly important with increasing azimuthal harmonic number, the computed results show that the effect is negligible for realistic Reynolds numbers.
A ray variability analysis of sound transmission from Heard Island to California.
Authors: Chiu Ching-Sang , Semtner Albert J. , Ort Coenraad M. , Miller James H. , Ehret Laura L.
Published: October 2005

In support of the Heard Island experimental effort, the influence of mesoscale and seasonal ocean variability on three-dimensional acoustic ray paths from Heard Island through the Indian and Pacific Oceans to the California coast is investigated. For the simulation of these global acoustic ray paths, a three-dimensional Hamiltonian ray tracing code is used. The input sound-speed fields to the acoustic ray model are interpolated from gridded temperature and salinity output data from the Semtner–Chervin eddy-resolving, global, general circulation model. A previous ray analysis was conducted using ocean fields containing only the mesoscale variability. This analysis provided input to experimental planners for receiver placement off the California coast [C. S. Chiu and A. J. Semtner, J. Acoust. Soc. Am. Suppl. 1 88, S92–S93 (1990)]. Here, a new analysis is presented that includes the acoustic effects of ocean seasonal cycles. In particular, the variability of the paths, arrival azimuthal angles, and travel times are discussed.
The frequency scale of speech intonation
Authors: Hermes Dik J. , van Gestel Joost C.
Published: October 2005

In intonation research, prominence-lending pitch movements have either been described on a linear or on a logarithmic frequency scale. An experiment has been carried out to check whether pitch movements in speech intonation are perceived on one of these two scales or on a psychoacoustic scale representing the frequency selectivity of the auditory system. This last scale is intermediary between the other two scales. Subjects matched the excursion size of prominence-lending pitch movements in utterances resynthesized in different pitch registers. Their task was to adjust the excursion size in a comparison stimulus in such a way that it lent equal prominence to the corresponding syllable in a fixed test stimulus. The comparison stimulus and the test stimulus had pitches running parallel on either the logarithmic frequency scale, the psychoacoustic scale, or the linear frequency scale. In one-half of the experimental sessions, the test stimulus was presented in the low register, while the comparison stimulus was presented in the high register, and, conversely, for the other half of the sessions. The result is that, in all cases, stimuli are matched in such a way that the average excursion sizes in different registers are equal on the psychoacoustic scale.
Evidence for two discrete sources of 2f1−f2 distortion-product otoacoustic emission in rabbit: I. Differential dependence on stimulus parameters
Authors: Whitehead M. L. , Lonsbury-Martin B. L. , Martin G. K.
Published: October 2005

The results of studies of the physiological vulnerability of distortion-product otoacoustic emissions (DPOAEs) suggest that the DPOAE at 2f1−f2 in vertebrate ears is generated by more than one source. The principal aims of the present study were to provide independent evidence for the existence of more than one DPOAE source, and to determine the contributions of each to the ear-canal 2f1−f2 signal. To accomplish these aims, specific stimulus parameters were separately and systematically varied to provide detailed parametric information regarding 2f1−f2 DPOAE amplitude and phase in normal ears of awake rabbits. The findings indicate that two discrete sources, demonstrating differential dependence on stimulus parameters, dominate the generation of the 2f1−f2 DPOAE. One source of distortion is dominant above 60–70 dB SPL at moderate primary-frequency separations, and at all stimulus levels when the primary tones are closely spaced. The other source is dominant below 60–70 dB SPL at moderate primary-frequency separations, and may be dominant at all stimulus levels when the primary tones are widely separated in frequency. The results suggest that by varying stimulus parameters, it may be possible to independently study the two generator mechanisms.
An auditory psychometric function from newborn chicks
Authors: Gray Lincoln
Published: October 2005

This study shows how the hearing of newborn chicks can be quantified with receiver operating characteristics (ROCs). A detailed auditory psychometric function was constructed from areas under ROCs, derived from delays in ongoing vocalizations elicited by pulsing pure tones. Over 20 000 delays were analyzed from 160 birds tested at four frequencies (0.25–2 kHz), eight intensities (−3 to 18 dB above estimated threshold), and two ages (0 and 4 days posthatch). Areas under these ROCs increase in an S-shaped function over intensity, as expected. Maximum responsiveness at approximately 75% correct shows that these neonates never achieve the near-perfect performance of mature listeners. Thresholds appear best estimated by the level required for 65% correct. Results replicate previous findings, showing that thresholds mature at low frequencies before high. Although there is no simple way to alleviate decreasing responsiveness caused by habituation over trials, improved performance results from presenting different frequencies, but only in the younger birds, and primarily with louder stimuli.
A model of head-related transfer functions based on principal components analysis and minimum-phase reconstruction
Authors: Kistler Doris J. , Wightman Frederic L.
Published: October 2005

Free-field to eardrum transfer functions (HRTFs) were measured from both ears of 10 subjects with sound sources at 265 different positions. A principal components analysis of the resulting 5300 HRTF magnitude functions revealed that the HRTFs can be modeled as a linear combination of five basic spectral shapes (basis functions), and that this representation accounts for approximately 90% of the variance in the original HRTF magnitude functions. HRTF phase was modeled by assuming that HRTFs are minimum-phase functions and that interaural phase differences can be approximated by a simple time delay. Subjects’ judgments of the apparent directions of headphone-presented sounds that had been synthesized from the modeled HRTFs were nearly identical to their judgments of sounds synthesized from measured HRTFs. With fewer than five basis functions used in the model, a less faithful reconstruction of the HRTF was produced, and the frequency of large localization errors increased dramatically.
Vibrotactile forward masking as a function of age
Authors: Gescheider George A. , Valetutti Anthony A. , Padula Michele C. , Verrillo Ronald T.
Published: October 2005

Thresholds for the detection of a 50-ms test stimulus delivered to the thenar eminence were measured as a function of the time interval between the offset of a 500-ms masking stimulus and the onset of the test stimulus (Δt). The frequency of the masker and the test stimulus was the same during a particular testing session and was either 25 or 250 Hz. At all values of Δt, older subjects exhibited significantly more masking than did young subjects. The effects of age were greater for stimuli that primarily affect the Pacinian system (250 Hz) than those that primarily affect non-Pacinian systems (25 Hz). Psychophysical measurements of the apparent duration of tactile sensations suggest that both sensory persistence and adaptation are affected by aging. Since adaptation seemed to be the more dominant factor for stimuli with durations as long as 500 ms, it was concluded that the effects of aging on forward masking seen in our study were due mainly to increased amounts of adaptation produced by the masker.
Acoustic analysis and perception of vowels in children’s and teenagers’ stuttered speech
Authors: Howell Peter , Williams Mark
Published: October 2005

The syllable repetitions of 24 child and eight teenage stutterers were investigated to assess whether the vowels neutralize and, if so, what causes this. In both groups of speakers, the vowel in CV syllable repetitions and the following fluent vowel were excised from conversational speech samples. Acoustic analyses showed the formant frequencies of vowels in syllable repetitions to be appropriate for the intended vowel and the duration of the dysfluent vowels to be shorter than those of the fluent vowels for both groups of speakers. The intensity of the fluent vowels was greater than that of the dysfluent vowels for the teenagers but not the children: For both age groups, excitation waveforms obtained by inverse filtering showed that the excitation spectra associated with dysfluent vowels fell off more rapidly with frequency than did those associated with the fluent vowels. The fundamental frequency of the children’s dysfluent speech was higher than their fluent speech while there was no difference in the teenager’s speech. The relationship between the intensities of the glottal volume velocities was the same as that of the speech waveforms. Perceptual tests were also conducted to assess whether duration and the differences found in the source excitation would make children’s vowels sound neutral. The experiments show that in children neither vowel duration nor fundamental frequency differences cause the vowels to be perceived as neutral. The results suggest that the low intensity and characteristics of the source of excitation which cause vowels to sound neutral may only occur in late childhood. Furthermore, monitoring stuttered speech for the emergence of neutral vowels may be a way of indexing the progress of the disorder.
The effect of wave reflection and refraction at soft tissue interfaces during ultrasound hyperthermia treatments
Authors: Fan Xiaobing , Hynynen Kullervo
Published: October 2005

An improved numerical model for calculating the ultrasonic power deposition in layered medium was developed and experimentally tested. The new model takes into account the ultrasound wave reflection and refraction at the tissue interfaces thereby providing improved accuracy in ultrasound hyperthermia treatment planning. The model was compared with a simplified model to evaluate when the tissue interfaces could be ignored in the hyperthermia treatment planning and evaluation. The effect of variations in water and tissue temperatures, the fat layer thicknesses, and the beam entrance angle were also investigated to establish guidelines for treatment execution. It was found that in most cases the effects of the soft tissue interfaces can be ignored. However, in some instances the acoustic focus may be shifted several millimeters off axis in layered medium. This is important when sharply focused transducers are used for ultrasound surgery or under the condition of pulsed, high-temperature hyperthermia treatments.
Effect of surficial sediment layering on high-frequency seafloor reverberation
Authors: McDaniel Suzanne T.
Published: October 2005

Perturbation theory is applied to predict the effects of surficial sediment layering on high-frequency acoustic backscatter from the seafloor. The case of a thin rough surface layer over a rough homogenous half-space is considered in which the surface and half-space roughnesses are partially correlated. The theory predicts strong interference effects near the critical angle similar to the anomalous scatter observed in recent field exercises.
A two-way parabolic equation for acoustic backscattering in the ocean
Authors: Collins Michael D. , Evans Richard B.
Published: October 2005

The parabolic equation (PE) method is generalized to handle backscattered acoustic energy in the ocean. The two-way PE is based on the single-scattering approximation and the approach of two-way coupled modes in which range-dependent environments are approximated by a sequence of range-independent regions. At the vertical boundaries between regions, the solution of the two-way PE is required to satisfy two continuity conditions. The range derivative in one of the conditions is replaced by a higher-order PE depth operator. The reflected and transmitted fields that satisfy these conditions are computed with an efficient iteration scheme. The outgoing and incoming fields are propagated by two-way range marching. The two-way PE, which is presently implemented for two-dimensional problems, is a practical method for solving large-scale reverberation problems. The accuracy of the two-way PE is demonstrated by comparisons with reference solutions. The two-way PE is applied to simulate the localization of a source of backscattering using the method of back propagation.
Note on averaged horizontal refraction for long distance propagation in an ocean sound channel
Authors: Dysthe Kristian B.
Published: October 2005

Long distance propagation in an ocean sound channel is considered, in the adiabatic limit. It is shown how the vertical oscillation of rays within such a channel can be averaged out so that one is left with equations describing the horizontal refraction. A modified Fermat’s principle for the averaged, horizontally projected rays is formulated. These results are also generalized to take into account: First, the effect of the Earth’s curvature, and then the effect of the phase shifts suffered by sound waves on hitting an external surface, or a caustic.
Ray synthesis of leaky Lamb wave contributions to backscattering from thick cylindrical shells
Authors: Sun N. H. , Marston P. L.
Published: October 2005

The ray representation of the scattering from an empty cylindrical shell is compared with the exact results of the partial-wave series. The specific example considered is a thick stainless steel shell having the same parameters as a previous synthesis for spheres illustrated by Kargl and Marston [J. Acoust. Soc. Am. 89, 2545–2558 (1991)]. The present computation demonstrates a general agreement with the exact result for ka down to 7 and confirms the applicability of a simple approximation for the complex coupling coefficient.
Nonlinear damping of bubble oscillations by resonant interaction
Authors: Longuet-Higgins Michael S.
Published: October 2005

In acoustical pulses from surface-generated bubbles, the observed rates of decay are sometimes anomalously high. In many instances, nonmonotonic behavior is observed. Here, it is shown that such effects can be produced by a resonant transfer of energy between the radial mode of oscillation, with radian frequency ω, and a ‘‘shape oscillation’’ of frequency σn, provided 2σn/ω is close to unity. In this phenomenon, the most important parameter is the proportional amplitude ε of the surface displacement in the breathing mode relative to the mean radius, compared with the proportional rate of damping βn/ω in the shape oscillation. The theory is applied in particular to three types of oscillation observed by Medwin and Beaky [J. Acoust. Soc. Am. 86, 1124–1130 (1989)] in their anechoic water-wave channel. A quantitative agreement is found. From a fit to the data, it is possible to deduce further parameters of interest, such as the limiting steepness of the shape oscillations before the spin-off of smaller bubbles, and the distance of the radiating bubble from its parent surface.
The sound of ice break-up and floe interaction
Authors: Xie Yunbo , Farmer David M.
Published: October 2005

When landfast ice breaks up and starts to move under the influence of wind and current, it produces a distinctive acoustical signature that can include nearby pure tones. Observations of this signal obtained in Amundsen Gulf are interpreted in terms of the initial fracturing mechanism followed by the rubbing of adjacent ice floes. The ice rubbing sound excites SH waves in the ice that evidently dominate the response, resulting in the pure tone that is observed. The frequency of this signal is determined by ice thickness and the shear wave speed.
Plane-wave analysis of the near field of light diffracted by ultrasound
Authors: Blomme Erik , Leroy Oswald
Published: October 2005

Although the phenomenon of light diffraction by ultrasound has been studied very extensively during the last 40 years, almost all investigations were concentrated on the individual far field (Fraunhofer) diffraction orders. In the present paper, the basic theory is developed for studying the near field (Fresnel region) of light diffracted by an arbitrary plane ultrasonic wave and the fundamental periodicity properties are stated. The general plane-wave theory of Raman–Nath has been taken as a starting point. From the analysis, the near field of the diffracted light is seen to be highly sensitive to variations of the ultrasonic amplitude and this feature provides a useful technique for observing weak ultrasonic waves. In particular, for the specific case of Raman–Nath-type diffraction, a procedure is presented allowing the reconstruction of the time waveform of the ultrasonic wave from the diffracted light intensity signal.
Comparison of multiple scattering theories with experimental measurements in emulsions
Authors: McClements David J.
Published: October 2005

The ultrasonic velocity and attenuation coefficient of a series of n-hexadecane-in-water emulsions have been measured as a function of disperse phase volume fraction (φ=0 to 0.56), particle size (r32=0.1 to 1.8 μm), and frequency ( f=0.2 to 7 MHz). These measurements are compared with predictions of the velocity and attenuation made using the multiple scattering theories of Waterman and Truell [J. Math. Phys. 2, 512–537 (1962)], Lloyd and Berry [Proc. Phys. Soc. London 91, 678–688 (1967)], and Ma et al. [J. Acoust. Soc. Am. 87, 2779–2782 (1990)] in the long wavelength limit. All the theories give good agreement with the experimental measurements for dilute emulsions (φ<0.13). In the more concentrated emulsions the theories agree less well, especially at low frequencies and particle sizes. Possible reasons for the discrepancies between the theories and experimental results are discussed.
Time domain Doppler estimators of the amplitude of vibrating targets
Authors: Huang Sung-Rung , Lerner Robert M. , Parker Kevin J.
Published: October 2005

Five basic algorithms using time domain techniques are described in this paper to estimate the amplitude and frequency of relatively low-frequency vibration of a target that is interrogated with a relatively high-frequency wave. The estimations are based on the Doppler shift generated by the vibrating target, which produces a frequency modulated echo. All algorithms presented here use only a small fraction of the low-frequency vibration cycle to obtain the estimated parameters; therefore, real-time imaging of vibration can be made in many applications. The described algorithms complement each other to cover a wide range of the estimated parameters and different sampling, scanning, and imaging criteria. Simulations show that these time domain algorithms have good noise performance and low sensitivity to nonlinearities of the vibration that may be present in nonideal conditions.
Floquet waves in anisotropic periodically layered composites
Authors: Braga Arthur M. B. , Herrmann George
Published: October 2005

The field equations governing the plane harmonic elastic motions of anisotropic stratified media are written in the form of a matrix system of differential equations, where the dependent variables are the displacements and tractions acting across planes normal to the direction of stratification. In the case of periodically layered media, Floquet’s theorem and the propagator matrix method can be applied to solve the governing sextic matrix equation. In the absence of sources or body forces, the general motion of the layered medium is described by a combination of six partial waves (Floquet waves). A closed-form algebraic solution for the dispersion equation of such waves is derived. Numerical results describing the dispersion spectrum of a cross-ply periodic laminated are discussed in detail.
The influence of piezoelectricity on free and reflected waves from fluid-loaded anisotropic plates
Authors: Nayfeh Adnan H. , Chien Hual-Te
Published: October 2005

A unified analytical treatment is presented supported by extensive numerical illustrations of the interactions of ultrasonic waves with piezoelectric anisotropic plates. The plates are allowed to possess up to monoclinic anisotropic symmetry and associated piezoelectric coupling. The plates are also assumed to be immersed in water and subjected to incident acoustic beams at arbitrary polar and azimuthal angles. Simple analytical expressions for the reflection and transmission coefficients are derived, from which all propagation characteristics are identified. Such expressions contain, as a by-product, the secular equation for the propagation of free harmonic waves on the piezoelectric plates. This equation is written in simple and completely separate terms pertaining to symmetric and antisymmetric modes. It is found that piezoelectric coupling, as well as water, influence both types of modes. Higher symmetry, such as orthotropic, transverse isotropic, and cubic, are contained implicitly in this analysis. It is also demonstrated that the motion of the sagittal (Lamb) and SH modes uncouple for propagation along axis of symmetry. For such cases, however, piezoelectric coupling can influence one of these types of modes depending upon the type of piezoelectric model adopted.
Reflection of sound waves by sound-speed inhomogeneities
Authors: Gingold Harry , She Jianming , Zorumski William E.
Published: October 2005

An analysis is given of the influence of the rate of change of sound speed on reflection and transmission in a perfect gas. Asymptotic formulas, valid for both low and high frequencies, are developed to compute the reflection and transmission coefficients for one-dimensional waves propagating through variable-speed layers. The sound speed may have a discontinuous first derivative. It is shown that local reflection effects are proportional to the square of the derivative of the logarithm of the sound speed. The method predicts reflections for gradually varying sound-speed profiles having continuous derivatives of all orders. In the special case where the sound speed is a piecewise linear function, the general method produces an exact solution in addition to the asymptotic formulas. This exact solution is valid for arbitrarily large sound-speed gradient and reduces to the classical result for discontinuous sound speed in the limit of an infinite gradient over an infinitesimal distance. The exact solution produces an effective numerical method when an arbitrary sound-speed profile is modeled by a mixed sequence of discontinuities and ramp functions.
Analysis and computations of measurement system effects in ultrasonic scattering experiments
Authors: Waag Robert C. , Astheimer Jeffrey P. , Smith James F.
Published: October 2005

A model that characterizes the effects of beams and waveforms on the measurement of ultrasonic scattering is analyzed in detail. The analysis obtains a wideband expression for the system function in terms of an integration over spatial- and temporal-frequency variables. The temporal-frequency integration is reduced to a convolution in the direction of the scattering vector when the temporal frequencies are concentrated in a narrow band around a central frequency. The spatial-frequency integration is simplified to a straight line path when the spatial frequencies in the angular spectra of the emitter are concentrated around a point on the axis of the emitter and the spatial frequencies of the detector sensitivity pattern are similarly concentrated around a point on the axis of the detector. Expressions that result from the temporal and spatial approximations are evaluated analytically for circularly symmetric Gaussian spatial apertures and Gaussian temporal waveforms. In addition, numerical results are obtained to compare the effects of circularly symmetric Gaussian, exponential, and uniform spatial aperture functions on the weight that beam patterns have on measurements of scattering. The results may be used to design experiments from which intrinsic parameters of scattering media can be obtained by an appropriate normalization to remove measurement system effects from the data.
Production of structural and acoustic waves by dipole sources adjacent to an elastic plate with a pressure-release coating
Authors: Howe M. S.
Published: October 2005

Model problems are examined to estimate the influence of a pressure-release coating on an elastic plate on the generation of sound and vibration by hydroacoustic dipole sources. Predictions for this idealized case provide useful first approximations to the behavior of real systems in which the fluid loading is large. The dipole and plate may be assumed to characterize, respectively, the unsteady lift exerted on a blade of a ducted rotor or stator during interaction with vorticity (occurring either naturally in a turbulent stream or as discrete vortices shed from structural appendages), and the adjacent duct wall. Such longitudinal dipoles (oriented parallel to the duct axis) produce equal and opposite images in a pressure-release coating, and the efficiency of sound generation is reduced to that of a quadrupole source when the dipole is situated well within an acoustic wavelength of the wall. In practice, considerations of cost and weight require that only a finite section of the duct wall be coated. In this paper, the dependence of the structural and acoustic noise produced by a dipole on its distance from an edge of the coated region, and on its normal distance from the coating, is determined.
Analysis of three-dimensional acoustic scattering from doubly periodic structures using a source model
Authors: Boag Amir , Leviatan Yehuda , Boag Alona
Published: October 2005

A novel solution is presented for the problem of three-dimensional acoustic scattering of a time-harmonic plane wave from doubly periodic structures. The general problem is first reduced to a consideration of the fields over a suitably defined unit cell. Sets of fictitious doubly periodic and properly modulated patch sources are used to simulate the fields in the homogeneous regions crossed by the unit cell boundaries. Sets of fictitious point sources are used to simulate the fields inside the regions completely enclosed within the unit cell. The complex amplitudes of the fictitious sources are adjusted to satisfy the boundary conditions at a selected set of points on the boundaries between the regions. The suggested solution procedure is simple to implement and is applicable to doubly periodic structures composed of homogeneous regions of arbitrary shape. Structures comprising acoustically rigid and soft boundaries can also be handled by the procedure. The method has been tested for accuracy by studying the cases of scattering from arrays of spherical scatterers and from doubly periodic sinusoidal surfaces.
Acoustical resonances of solid elastic cylinders: Parametric study and introduction to the inverse problem
Authors: Batard H. , Quentin G.
Published: October 2005

In underwater acoustics, target recognition is of major importance. In order to reach such a goal, one must solve the inverse problem to deduce from the received echoes the signature of the target. A rigorous method would require an inversion of the exact direct problem which is, at the present time, not feasible because of the complexity of the analytical expressions involved even for an isotropic, homogeneous, elastic cylinder. After trying different approximate alternative methods of resolution of such problems in this lab, a new method is presented in this paper. Its basis is a parametric study of resonance frequencies and widths, and some simple approximate expressions deduced from this work are used to solve the inverse problem. This study leads to a new classification of most resonances connected with the polarization of the corresponding waves. The frequencies of such resonances are given by very simple equations that can be very easily inverted. After carrying out this procedure, this model is applied to the characterization of the mechanical properties of a cylinder with a given radius a (longitudinal wave velocity cL, shear wave velocity cT, density ρ2 ). The first application concerns simulated resonance spectra and the second application concerns real experimental measurements. The results obtained are very satisfactory.
Inversion of acoustic material signature of layered solids
Authors: Kundu Tribikram
Published: October 2005

The simplex inversion technique is applied to the acoustic material signature (AMS) of layered solids to obtain thickness and material properties of layers. It is shown in this paper that by careful application of the simplex technique, it is possible to extract much information about a multilayered specimen from its AMS. A brief review of different inversion techniques is also given in the paper from which the relative advantages of using the simplex alogrithm over other techniques are derived.
Scattering from a finite cylindrical shell
Authors: Tran-Van-Nhieu Michel
Published: October 2005

An asymptotic solution of scattering from a finite slender cylindrical shell is derived from the two-variable expansions method by modifying the usual concept of secular terms. An analytical expression for the scattered far field is obtained from a superposition of sectorial spherical harmonics that have been used to describe scattering from slender bodies. The contribution of the scattered resonant pressure due to the elasticity of the material is analyzed and some numerical computations are made in monostatic and bistatic cases for rigid and elastic shells to evaluate the importance of the radiation of the resonant modes in the far field.
Evaluating acoustic absorption coefficients by comparative analysis—Experimental part
Authors: Mills Charles A. , Spiekermann Charles E.
Published: October 2005

A new method has been developed for evaluating normal incidence acoustic absorption coefficients of a material by making direct comparisons between experimental and analytical acoustic pressure magnitudes. The method uses an analytical model for an acoustic impedance tube having a closed and partially absorptive boundary, corresponding to an absorber specimen mounted within an endcap affixed to the tube. Additionally, the model incorporates internal acoustic dissipation effects associated with the apparatus. From the composite model, acoustical frequency response functions are computed based on the amounts of the two dissipation mechanisms. An algorithm is implemented whereby the response magnitudes measured at tube resonance frequencies are compared to corresponding analytical values so as to evaluate the absorption levels needed for a match. Since the absorption coefficients are evaluated for resonant modes only, a B-Spline curve is used to interpolate the results. The normal incidence acoustic absorption coefficient is then specified at all frequencies within a measurement spectrum. Experimental results are presented for a foam acoustic material and a comparison is made to the results from the standing wave method (ASTM C 384-90). The comparison shows a good correlation between the two.
A scattering model for nondifferentiable periodic surface roughness
Authors: Bishop Garner C. , Smith Judy
Published: October 2005

Ice dendrites that form when seawater freezes produce a surface with periodic roughness. This surface may be modeled by joining a concave upward semiellipse to a concave downward semiellipse and replicating this fundamental surface element to form a surface that is everywhere continuous, but is not differentiable at the points where the two ellipses are joined (i.e., the derivative is infinite). This surface is regarded as realization of the class of periodic rough surfaces that are not differentiable at a finite number of points within a period and includes surfaces that are piecewise and nonpiecewise smooth. A model is described to calculate plane-wave scattering from one-dimensional realizations of these types of surfaces. To calculate scattering from these types of surfaces for the physical parameters of interest, the integral equation formalism of Holford [J. Acoust. Soc. Am. 70, 1116–1128 (1980)] is used and the surface roughness profile is approximated by truncating its Fourier series representation. This approximation provides a continuous and differentiable representation of the surface roughness profile and is necessary to guarantee a convergent solution for the surface field that is obtained as a solution to a Fredholm integral equation of the second kind. The scattering theory of DeSanto [Radio Sci. 16, 1315–1326 (1981)] that uses Green’s theorem and a modified physical optics representation of the surface field is used to determine the effect of the approximation on the surface field and scattering amplitudes in the domain in which the theory is numerically stable (This theory is not numerically stable for the physical parameters of interest.)

Since this technique may be applied to any nondifferentiable surface that may be represented by a Fourier series, several nondifferentiable periodic surfaces are constructed. Numerical calculations show that the amplitudes of the plane-wave modes scattered from a continuous and nondifferentiable surface and from its truncated Fourier series representation are essentially identical over a wide range of incident grazing angles, acoustic frequencies, surface roughness, and surface types. Additionally, it is shown that when an integral equation is used to calculate scattering from a truncated Fourier series representation of a continuous and nondifferentiable surface, scattering may be calculated from surfaces considerably rougher than those considered previously.
Linearization of the matched field processing approach to acoustic tomography
Authors: Tolstoy A.
Published: October 2005

This paper continues the approach presented in Tolstoy et al. [J. Acoust. Soc. Am. 89, 1119–1127 (1991)] but offers a much improved inversion technique, i.e., a linearization of the problem which reformats the computations in terms of a simple nonsquare matrix inversion for an overdetermined system. This work was motivated by the desire to improve upon the speed and accuracy of the original algorithm that had a tendency to stall unpredictably [Tolstoy and Frazer, in Computational Acoustics, edited by D. Lee, A. Cakmak, and R. Vichnevetsky (North-Holland, Amsterdam, 1991)]. This work has the additional bonus that sound-speed accuracies are now an order of magnitude better than the earlier technique. In addition, calculations confirm that for simulations with white, Gaussian, uncorrelated noise the linear/Bartlett processor results are identical to those of the minimum-variance/Capon processor. Finally, optimal source–receiver configurations have been determined by exhaustively computing the condition numbers for the associated matrices in the new linear formulation. Simulation results with the new linearization plus matrix inversion scheme show that three arrays located at optimal coordinates in a 250×250-km ocean region with shot sources distributed around the perimeter can result in 3-D sound-speed profiles determined to accuracies better than 0.07 m/s and better than 0.03 m/s for four arrays located at optimal coordinates (assuming perfect knowledge of sound-speed profiles at source and array coordinates, no array deformations, perfect elimination of bottom interacting energy). Such accuracies are not to be expected under experimental conditions.
Three-dimensional time-domain paraxial approximations for ocean acoustic wave propagation
Authors: Orchard B. J. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

One-way narrow- and wide-angle three-dimensional time-domain paraxial approximations to the wave equation are developed to model acoustic propagation. The approximate equations are designed to be appropriate for ocean applications including pulse propagation with volume attenuation and variable density. First, differential equations for acoustic pressure are obtained from a thermodynamic model, which incorporates attenuation due to the presence of acoustically absorbing chemical species. The method of multiple scales is then used to generate partial differential equations with paraxial characteristics. Comparisons are made to corresponding previous results. Results from an operator formalism using Padé approximants are subsequently compared with the corresponding multiscaling results. Appropriate boundary, initial, and interface conditions are described for the model equations. Stability of the three-dimensional narrow-angle approximation is demonstrated by means of an energy integral. Analytical expressions for pulse-type solutions to a special case of the narrow-angle equation are obtained. Comparisons with exact solutions to the full-wave equation solution demonstrate the validity of the model when certain asymptotic constraints are observed.
Weakly nonlinear waves generated by vibration of a spherical body
Authors: Yano Takeru , Inoue Yoshinori
Published: October 2005

The nonlinear propagation of directional spherical waves generated in an unbounded inviscid ideal gas by vibratory motions with small but finite amplitude and moderate frequency of a spherical body is considered. Starting with a regular perturbation expansion for a velocity potential in the near field, a higher-order problem is investigated in the far field up to the shock formation distance. It is thereby shown that, in the far field concerned, a well-known simple far-field equation remains valid for the radial velocity u*r including higher-order corrections up to O(εN/r) (N<−1/ε ln ε), where r is a nondimensional radial coordinate and ε(≪1) is the expansion parameter of the expansion. A boundary condition appropriate to the equation, which ensures the matching of a far-field solution with a near-field solution, can be determined from the near-field solution obtained by the regular perturbation procedure. As an application of the theory, the third-order problem is solved for weakly nonlinear acoustic waves radiated by a pulsating sphere. It is further shown that, for weakly nonlinear cylindrical waves with moderate frequency, a similar far-field equation becomes invalid at the third approximation in the far field up to the shock formation distance.
Effect of signal frequency and masker level on the frequency regions responsible for the overshoot effect
Authors: Carlyon Robert P. , White Louise J.
Published: October 2005

Two experiments investigated the relative influence of components close to and remote from the signal frequency ( fs) on the overshoot effect. Overshoot was defined as the difference in threshold between a signal presented 4 ms after, and that for one presented 300 ms after, the onset of a 350-ms masker. Experiment 1 measured the overshoot effect using both wideband and narrow-band maskers (centered on fs ), at two signal frequencies and three masker levels. Experiment 2 used a masker consisting of a ‘‘middle band’’ (MB, centered on fs ) and two flanking bands (FBs, which, when combined with the MB, produced a flat wideband spectrum). The masker was continuous except for a 300-ms interval just prior to the signal, during which either all three bands, the MB alone, or the FBs alone were turned off. The results of both experiments showed that the overshoot effect was usually determined by off-frequency components. However, the on-frequency components played a substantial role when signal-to-noise ratios (SNRs) at threshold were unusually high, such as at fs=6500 Hz and intermediate masker levels. It is suggested that two different mechanisms contribute to the overshoot effect: an off-frequency mechanism which operates at all fs and masker levels, and an on-frequency mechanism which contributes to the overshoot effect only at high-threshold SNRs.
Comodulation masking release for speech stimuli
Authors: Grose John H. , Hall Joseph W.
Published: October 2005

This study sought to determine whether speech recognition in a modulating noise background can be facilitated by a process attributable to comodulation masking release (CMR). Experiment 1 examined the masked identification of six filtered vowels as a function of the number of comodulated noisebands present. A benefit of increased number was observed, consistent with an interpretation in terms of CMR, although it could not be certain that the basis of the discrimination was word recognition in the semantic sense. Experiment 2 made use of a forced-choice rhyming test in which the response foils differed only in a single filtered consonant; again, the measure of interest was performance as a function of the number of comodulated noisebands present. No evidence for a suprathreshold CMR was observed. Experiment 3 made use of open-set sentence material and employed a different paradigm, which allowed a measure of CMR in terms of the difference between thresholds in correlated and uncorrelated noise to be determined. While a CMR for speech detection was observed, no CMR for speech recognition was found. It was concluded that CMR is most evident in masked detection tasks and that diminishing returns are encountered as the signal-to-masker ratio is raised.
Effect on signal-to-noise ratio of clipping arctic acoustic data after prefiltering
Authors: Zakarauskas Pierre , Hamm Craig A. , Thorleifson Jon M.
Published: October 2005

Arctic ambient noise is characterized by the presence of transients due to ice cracking. The present document reports the results of an investigation into the effect on signal-to-noise ratio (SNR) of clipping ambient noise time series to which artificial sinusoid signals had been added. Because the ambient noise contains more power at low frequencies than at high frequencies, it was deemed necessary to bandpass filter the time series before clipping. The effect of clipping on SNR was found to depend strongly on the center frequency of the bandpass filter. At low frequency (f≤40 Hz) the SNR was not greatly affected by clipping. At higher frequencies (80 Hz ≤f≤1280 Hz), however, clipping was found to improve the SNR, by as much as 5 dB.
Speech reception in quiet and in noisy conditions by individuals with noise-induced hearing loss in relation to their tone audiogram
Authors: Smoorenburg Guido F.
Published: October 2005

Tone thresholds and speech-reception thresholds were measured in 200 individuals (400 ears) with noise-induced hearing loss. The speech-reception thresholds were measured in a quiet condition and in noise with a speech spectrum at levels of 35, 50, 65, and 80 dBA. The tone audiograms could be described by three principal components: hearing loss in the regions above 3 kHz, from 1 to 3 kHz and below 1 kHz; the speech thresholds could be described by two components: speech reception in quiet and speech reception in noise at 50–80 dBA. Hearing loss above 1 kHz was related to speech reception in noise; hearing loss at and below 1 kHz to speech reception in quiet. The correlation between the speech thresholds in quiet and in noise was only R=0.45. An adequate predictor of the speech threshold in noise, the primary factor in the hearing handicap, was the pure-tone average at 2 and 4 kHz (PTA2,4, R=0.72). The minimum value of the prediction error for any tone-audiometric predictor of this speech threshold was 1.2 dB (standard deviation). The prediction could not be improved by taking into account the critical ratio for low-frequency noise nor by its upward spread of masking. The prediction error is due to measurement error and to a factor common to both ears. The latter factor is ascribed to cognitive skill in speech reception. Hearing loss above 10 to 15 dB HL (hearing level) already shows an effect on the speech threshold in noise, a noticeable handicap is found at PTA2,4=30 dB HL.