bluuebunny/crossref_metadata_2025 huggingface dataset:
Backscattering of underwater noise by bubble clouds
Authors: Sarkar K. , Prosperetti A.
Published: October 2005

This paper is a continuation of an earlier one [Prosperetti et al., J. Acoust. Soc. Am. 93, XXX (1993)] in which the low-frequency backscattering of sound by hemispherical bubble clouds at the ocean’s surface was studied. Here, clouds of various geometrical shapes (spheroids, spherical segments, cones, cylinders, ellipsoids) are considered and results in substantial agreement with the earlier ones and with the experiments of Chapman and Harris [J. Acoust. Soc. Am. 34, 1592–1597 (1962)] are found. The implication is that the backscattering levels are not strongly dependent on the shape of the clouds, which strengthens the earlier conclusion that bubble clouds produced by breaking waves can very well be responsible for the unexpectedly high backscattering levels observed experimentally. The accuracy of the Born approximation used by others for similar problems is also examined in the light of the exact results. Significant differences are found for gas concentrations by volume of the order of 0.01% or higher. Finally, shallow nonaxisymmetric plumes are briefly considered.
Acoustic properties of fine-grained sediments from Emerald Basin: Toward an inversion for physical properties using the Biot–Stoll model
Authors: Courtney Robert C. , Mayer Larry
Published: October 2005

Acoustic data from two long cores, comprising marine clays and silts taken from Emerald Basin off Nova Scotia, are presented. High-resolution measurements of compressional wave velocity, attenuation, and power law exponent are made using ultrasonic frequencies between 100 to 1000 kHz. The observed values of the frequency dependence of attenuation suggest that a nonconstant Q mechanism is needed to explain these data, and Biot–Stoll theory is used to model the experimental results. An inversion scheme is used to constrain physical parameters in the Biot–Stoll dispersion relation. The inversion shows that there is a restricted range of permeability and grain size. By assigning reasonable values for grain size in the inversion, the Biot–Stoll model predicts unique values for the permeability and frame bulk modulus that agree well with estimates made by other means.
Approximate evaluation of the spectral density integral for a large planar array of rectangular sensors excited by turbulent flowa)
Authors: Thompson William , Montgomery Robert E.
Published: October 2005

An approximate numerical procedure has been developed for rapidly evaluating the spectral density integral that predicts the output of a planar array of many sensors excited by turbulent boundary layer pressure fluctuations. This procedure is particularly useful in cases where the transfer function factor of the integrand is not a simple function of the wave numbers in the flow and transverse directions. The procedure exploits the facts that the entire integrand is a separable function of these two wave numbers and, when the number of sensors is large, the array function factor of the integrand is a rapidly varying function of wave number, characterized by many similar shaped lobes. In addition, a model for multilayered media is employed to provide the transfer function for boundary conditions that closely correspond to reality. Results generated by this procedure were compared to those from an exact evaluation of the integral which is possible if the transfer function is taken to be constant; there was agreement to within 0.2 dB or better over a broad frequency interval. Some results for a realistic transfer function are presented, such as the case of an elastomeric layer backed by an elastic plate with the sensors embedded at an arbitrary position within the layer.
Ultrasonic propagation, scattering, and defocusing in suspensions
Authors: Adach J. , Chivers R. C. , Anson L. W.
Published: October 2005

Fine resolution narrow-band pressure amplitude distribution measurements have been performed using a hydrophone in the field of a weakly focused bowl transducer radiating into castor oil and 1% and 2% by volume suspensions of 320-μm polystyrene beads in castor oil over the frequency range 1.0 to 2.5 MHz at 20 °C. The axial distributions permitted determination of the excess attenuation due to scattering in the suspensions as a function of frequency. The frequency range included a resonance. The excess attenuation measured was compared with the theoretical predictions of Waterman and Truell [J. Math. Phys. 2, 512–537 (1961)] and good agreement was obtained. The values of the excess attenuation obtained were used to predict axial pressure amplitude distributions in the suspension. Although the excess attenuation was determined from far-field measurements, the agreement between the predicted axial distributions and those measured experimentally extended well into the near field. Lateral distributions were measured at seven frequencies at the position of the geometrical center of curvature of the source and at the position of the true focus in the 1% suspension. Comparison with similar scans in castor oil alone revealed no detectable defocusing due to the presence of the scatterers.
Ultrasonic investigations of some polymeric materials
Authors: Singh D. P. , Pal Singh Anand
Published: October 2005

Ultrasonic investigations of some polymeric materials such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and polyethylene glycol at 303 K have been done using ultrasonic velocity and density data taken from the literature. Various acoustical parameters such as molar sound velocity, molar adiabatic compressibility, acoustic impedance, van der Waal’s constant, molar sound volume, free volume, internal pressure, and cohesive energy have been determined. A large number of thermodynamical parameters such as molar volume, available volume, geometrical volume, intermolecular free length, relative association, and surface tension have been evaluated. Jacobson’s free length theory and Schaaff’s collision factor theory have been used to predict the values of ultrasonic velocities in the systems under study. The obtained results have been compared with the experimental results available in literature. The variation of acoustical and thermodynamical parameters of these polymeric materials, with change in their molecular weight, provide a deep insight into the intermolecular interactions going on in these systems.
Acoustic distortion as a measure of frequency selectivity: Relation to psychophysical equivalent rectangular bandwidth
Authors: Brown Ann M. , Gaskill Sally A. , Carlyon Robert P. , Williams Deirdre M.
Published: October 2005

The magnitude of cubic intermodulation distortion generated when two tones are progressively separated in frequency reaches a broad maximum when the distortion frequency falls just over half an octave below the high-frequency stimulus (f2), when this distortion is measured with a microphone in the ear canal. For the component 2f1−f2, this peak occurs at an f2/f1 ratio of approximately 1.2. The tuning, magnitude, and mean group delay of this distortion peak was measured for a fixed f2 of 4 kHz at 40 dB SPL and a varied f1 at 55 dB SPL in eight human subjects with normal hearing. The distortion peak measures were compared with the frequency selectivity at 4 kHz of the same eight subjects derived using a forward-masking notched-noise paradigm. In the six subjects from whom good, repeatable levels of distortion were measured, a significant negative correlation was found between the tuning of the distortion peak and the psychophysical bandwidth at f2. It is concluded that the tuning of the distortion peak may provide an objective measure of frequency selectivity in the human cochlea.
Plane compression front steepening in nonlinear media forms both a shock and a reflected wave
Authors: Morfey C. L. , Sparrow V. W.
Published: October 2005

An exact solution is given for the reflected wave formed in a nonlinear medium when a plane compression front steepens into a shock. The solution predicts both a shock and a reflected wave. In the small-amplitude limit the reflected wave strength varies as (ΔP)3, where ΔP is the strength of the initial wave front.
An evaluation of the Kirchhoff approximation in predicting the axial impulse response of hard and soft disks
Authors: Norton Guy V. , Novarini Jorge C. , Keiffer Richard S.
Published: October 2005

To test the ability of the Kirchhoff approximation for estimating the various components in the near-field impulse response of a circular disk, the predictions from a time domain formulation of the Helmholtz–Kirchhoff solution [Trorey, Geophys. 35, 762–864 (1970)] are benchmarked against results obtained via the Fourier synthesis of highly accurate frequency domain solutions [Kristensson and Waterman, J. Acoust. Soc. Am. 72, 1612–1625 (1982)]. In these numerical experiments, a collocated point source and receiver lie on the symmetry axis of an acoustically hard (rigid) or soft (pressure release) disk. A time-domain analysis is carried out in order to unambiguously evaluate the Kirchhoff approximation for different components of the scattered field. It is found that, while Helmholtz–Kirchhoff predicts the correct reflected component, it fails to accurately predict the strength of the diffracted component. The magnitude of the error depends on whether the disk is soft or hard and on the source/receiver height above the disk. The error in the diffracted component exceeds, in some cases, 100%. Furthermore, it is observed that the Helmholtz–Kirchhoff approach does not include the secondary or multiply diffracted arrivals which are more pronounced for the hard disk.
Transient acoustic pressure radiated from a finite duct
Authors: Stepanishen P. , Tougas Rene A.
Published: October 2005

The time-dependent pressure radiated from a finite, rigid, circular duct of constant cross section is determined for the specified motion (velocity or acceleration) of a piston source within the duct. The modal composition of the internal field variables is represented as an eigenfunction expansion over the duct cross section, and a time- and space-dependent Green’s function is used to develop a generalized boundary condition which describes the effect of the external surroundings at the duct exit. Solution of this boundary value problem results in a duct transfer function which is then cascaded with the spatial transfer function connecting the duct exit port and a selected external field point. In this paper, inversion to the time domain is accomplished via the FFT algorithm. Numerical examples demonstrating the calculation of the external time-dependent pressure are presented based upon the specification of a gated sinewave piston acceleration over an assumed piston spatial profile. Confirming the theoretical analysis, the numerical results show that the time-dependent pressure for the cross modes develops its peak value off-axis and is always zero on-axis, while the plane wave mode always peaks precisely on-axis.
Minimax robust matched-field processing
Authors: Gingras Donald F. , Gerr Neil L.
Published: October 2005

The incorporation of propagation modeling into array signal processing, usually referred to as ‘‘matched-field processing,’’ has received considerable attention. The issue of the sensitivity of the performance of these methods to uncertainty about the environmental knowledge remains an open issue. In this paper broadband processing methods that are tolerant of the uncertainty about environmental knowledge are investigated. A robust matched-field processor based on minimax robust filtering methods is developed. The performance of the robust processor, in the presence of uncertain environmental knowledge, is compared to conventional methods in the context of a shallow water example. In the cases examined the robust method provided significant performance improvements over conventional methods.
Quantifying ear-canal geometry with multiple computer-assisted tomographic scans
Authors: Egolf David P. , Nelson David K. , Howell Henry C. , Larson Vernon D.
Published: October 2005

Several audiological tests require knowledge of the sound-pressure spectrum at the eardrum. However, microphone readings are typically made at another, more-accessible position in the auditory canal. Recordings are then ‘‘adjusted’’ to the plane of the eardrum via mathematical models of the ear canal and eardrum. As bandwidths of audiological instruments have increased, ear-canal models have, by necessity, become more precise geometrically. Reported herein is a noninvasive procedure for acquiring geometry of the ear canal in fine detail. The method employs a computer-assisted tomographic (CAT) scanner in two steps to make radiographic images of parasagittal cross sections at uniform intervals along the lateral length of the canal. Accuracy was evaluated by comparing areas of cross sections appearing in radiographic images of a cadaver ear canal to cross sectional areas of corresponding michrotome slices of an injection mold of the same canal. Percent differences between these two areas had a mean value of 9.65% for 26 different cross sections of the one ear canal studied. Ear canal volume estimated from the CAT images was 6.12% different from the estimated volume of the injection mold: an improvement over the reported 39% maximum error of conventional acoustic volume measurements.
Distortion-product otoacoustic emissions in the bobtail lizard. I: General characteristics
Authors: Manley Geoffrey A. , Köppl Christine , Johnstone Brian M.
Published: October 2005

In the ear canal of the bobtail lizard, both emitted harmonics and distortion products (DP) were measured, some of which were sensitive to hypoxia. The minimal levels of primary tones for the production of DP corresponded closely to the best auditory-nerve fiber thresholds for this lizard species. DP originating from the two segments of the basilar papilla (which respond to different frequency ranges) differed in a number of respects. DP from the higher-frequency segment bore a remarkable resemblance to the acoustic DP of mammals in many details, in spite of substantial structural and micromechanical differences between these hearing organs, suggesting that it is the characteristics of the hair cells themselves that are the most important factors determining DP generation. Also, DP clearly originated in the high-frequency region of this lizard papilla, where single-nerve fibers do not show two-tone rate suppression, another nonlinear phenomenon. In some cases, the DP level was clearly affected by the presence of spontaneous otoacoustic emissions. The frequency selectivity of the DP 2 f1−f2 and 2 f2−f1 in the bobtail lizard was also studied, by measuring thresholds of DP detection while varying the frequency ratio of the primary tones. The characteristics of tuning in high-frequency DP showed some remarkable similarities to the tuning curves of single-nerve fibers, suggesting that the characteristics of acoustic DP produced by low-level primary tones were determined by the tuning characteristics of the hearing organ at the hair-cell level.
Comodulation masking release: Is comodulation sufficient?a)
Authors: Grose John H. , Hall Joseph W.
Published: October 2005

Common amplitude modulation across frequency facilitates comodulation masking release (CMR) and may also contribute to auditory grouping. The purpose of the present investigation was to determine whether there is an association between these two phenomena; that is, does the occurrence of CMR require that the comodulated noise bands making up the composite masker be grouped together? Three experiments were undertaken, each manipulating one variable designed to hinder the fusion of the comodulated noise bands. In experiment 1, the variable of onset/offset asynchrony was observed to have a marked effect: CMR could be completely abolished if the asynchrony between the on-signal band and the flanking bands was sufficiently great (≥50 ms). In experiment 2, an auditory streaming paradigm was employed and this was observed to disrupt CMR significantly. However, a substantial CMR remained. Experiment 3 attempted to hinder the fusion of the comodulated noise bands by drawing the various noise bands into separate harmonic series. However, the small effect observed did not appear to be due to a parsing of the fused image. Results from experiments 1 and 2 suggest that the CMR mechanism does not act in isolation from the processes that give rise to auditory object formation. In particular, the cue of onset/offset synchrony appears to be of paramount importance.
Uncomodulated glimpsing in ‘‘checkerboard’’ noise
Authors: Howard-Jones Paul A. , Rosen Stuart
Published: October 2005

The ability of listeners to ‘‘glimpse’’ acoustic cues during the quieter sections of an interrupted noise has primarily been studied using maskers with interruptions occurring simultaneously across the entire frequency range of the masker—broadband comodulated interruptions. Here, the possibility of uncomodulated glimpsing (the glimpsing of acoustic cues separated both in time and frequency) was investigated. To achieve this, speech reception thresholds for a set of intervocalic consonants were adaptively measured in 100-Hz to 10-kHz pink noise divided into a varying number of frequency bands of equal energy. In uncomodulated noise conditions, the odd and even numbered bands were switched on and off alternately at a rate of 10 Hz. The spectrograms of such noises (on log frequency scales), resemble portions of a checkerboard. Glimpsing in ‘‘checkerboard’’ noise was found with maskers divided into two and four bands, but not into eight bands or more. Further investigations showed that, in the two-band case, this release from masking was indeed due to uncomodulated glimpsing, and not simply attributable to glimpsing in one of the modulated bands. In the four-band case, the release from masking in checkerboard noise can be accounted for without recourse to uncomodulated glimpsing. Interestingly, conditions which allowed glimpsing resulted in greater intersubject variability. The implications of these results for quantitative analyses of masker fluctuations are discussed.
Adjustment and discrimination measurements of the precedence effect
Authors: Shinn-Cunningham Barbara G. , Zurek Patrick M. , Durlach Nathaniel I.
Published: October 2005

A simple model to summarize the precedence effect is proposed that uses a single metric to quantify the relative dominance of the initial interaural delay over the trailing interaural delay in lateralization. This model is described and then used to relate new measurements of the precedence effect made with adjustment and discrimination paradigms. In the adjustment task, subjects matched the lateral position of an acoustic pointer to the position of a composite test stimulus made up of initial and trailing binaural noise bursts. In the discrimination procedure, subjects discriminated interaural time differences in a target noise burst in the presence of another burst either trailing or preceding the target. Experimental parameters were the delay between initial and trailing stimuli and the overall level of the stimulus. The model parameters (the metric c and the variability of lateral position judgments) were estimated from the results of the matching experiment and used to predict results of the discrimination task with good success. Finally, the observed values of the metric were compared to values derived from previous studies.
A database of subaquatic and hyperbaric speech: PSH/DISPE
Authors: Marchal Alain , Meunier Christine
Published: October 2005

The present article describes a French and English divers’ speech database, now implemented and available on a CDROM. This database complies with the SAM EUROPEC standards. It consists of acoustic signal files and associated files which provide information about the speakers and recording conditions. A database management system is used for an easy and fast retrieval of the speech items recorded at various depths and with specific diving equipment.
Detection and calibration of ultrasound using vibration potentials
Authors: Gist G. A. , Wilson M. D.
Published: October 2005

A simple procedure is described to provide an absolute calibration of ultrasonic compressional wave transducers in a water tank. The calibration makes use of the ionic vibration potential by measuring the electric potential wave that propagates with an acoustic wave in an ionic solution. The method has good spatial resolution and has been used to measure the beam profile and amplitude in absolute units of an ultrasonic pulse in a water tank.
Comments on ‘‘Computation of the equivalent modal impedance matrix of a multiple degree of freedom electroelastic structure using anti-resonance modes’’ [J. Acoust. Soc. Am. 90, 2891–2894 (1991)]
Authors: Johnson Michael P.
Published: October 2005

It is noted that while choice of anti-resonance modes as a set of basis functions in evaluating a modal impedance matrix is possible, no advantage is gained over resonance modes in the application to multiport network models. A brief discussion of the derived modal impedance matrix, its form, and computational considerations relative to multiport network techniques is used to illustrate this observation.
The variation of the specific heat ratio and the speed of sound in air with temperature, pressure, humidity, and CO2 concentration
Authors: Cramer Owen
Published: October 2005

This paper describes a precise numerical calculation of the specific heat ratio and speed of sound in air as a function of temperature, pressure, humidity, and CO2 concentration. The above parameters are calculated utilizing classical thermodynamic relationships and a real gas equation of state over the temperature range 0 °C–30 °C. The shortcomings of previous determinations are also discussed. For both parameters, the coefficients of an interpolating equation are given, which are suitable for use in applications requiring high precision. The overall uncertainty in the specific heat ratio is estimated to be less than 320 ppm and the uncertainty in the speed of sound is similarly estimated to be less than 300 ppm.
Low-frequency Arctic reverberation. II: Modeling of long-range reverberation and comparison with data
Authors: Yang T. C. , Hayward T. J.
Published: October 2005

In the Arctic ocean, very low-frequency (10–50 Hz) reverberation returns from the ice and bottom both contribute to the total received reverberation and are not easily distinguishable in long-range reverberation data, except where there is a dominant bottom or ice feature. In this paper, a normal-mode model of scattering from surface and bottom protuberances is applied to model long-range reverberation data collected during the CEAREX 89 experiment in the Norwegian/Greenland Seas. Modeled reverberation spectrum levels at 23 Hz are compared with data to investigate the relative contributions of the ice and bottom to the measured reverberation. The normal-mode model of boundary scattering is based on a generalization of recent work of Ingenito [F. Ingenito, J. Acoust. Soc. Am. 82, 2051–2059 (1987)] treating scattering from a rigid sphere in a stratified waveguide. Adiabatic normal mode theory is used to model the propagation to and back from the scatterer in a range-dependent waveguide. Using the small-ka approximation for the scattering functions, where k is the wave number and a is the dimension of the boundary protuberance, the normal-mode calculations of the long-range reverberation levels are found to agree rather well with the CEAREX data for four different measurements involving different bottom bathymetries and source depths. For a source at 91-m depth in the 3000-m-deep basin, it is found that the reverberation level for a receiver at 60 m is dominated by scattering from the ice except for reverberation associated with certain identifiable bottom features. For the same environment but a deeper (244-m) source, reverberation levels from the ice and bottom are more comparable. For a strongly range-dependent environment, returns from bottom features are clearly identifiable in the data.
Low-frequency volume reverberation measurements
Authors: Akal Tuncay , Dullea Robert K. , Guidi Guido , Stockhausen John H.
Published: October 2005

An experimental technique has been developed to measure broadband low-frequency volume reverberation. Experiments were performed in the North Atlantic with broadband explosive sources in conjunction with the end-fire beam of a vertical line array to provide scattering strength contours from measurements sampled in both frequency (∼12 Hz) and depth (∼4 m). The average effective resolution in frequency (∼100 Hz) and depth (∼30 m) resulted from signal processing procedures and geometrical effects associated with the measurements. During the measurements a SIMRAD scientific echo sounder system was utilized. This system incorporates split-beam processing technology to provide the most accurate in-situ assessment, analysis, and display of biological target strength and fish length distributions. The experimental and analysis techniques are described along with representative examples that compare high and low scattering levels observed during the experiment.
Modeling three-dimensional propagation in an oceanic wedge using parabolic equation methods
Authors: Fawcett John A.
Published: October 2005

In this paper the predictions of azimuthally uncoupled and azimuthally coupled parabolic equation (PE) methods for three-dimensional acoustic propagation in a penetrable oceanic wedge are compared. The individual modes of the waveguide at the source position are used as the initial field for the PE methods and the resulting PE fields are compared to the ray diagrams of three-dimensional adiabatic mode theory.
Experimental demonstration of sound-speed inversion with matched-field processing
Authors: Karangelen Carolyn C. , Diachok Orest
Published: October 2005

Matched-field processing is shown to be effective for estimating sound speed in a deep, range-independent ocean environment. The amplitude and phase of signals from a distant source measured on a large aperture vertical array are sensitive to changes in sound speed. This sensitivity is exploited to infer the environment’s sound-speed profile by matching predicted and measured amplitude and phase. Simulations and an initial experimental demonstration of the power of the technique are based on a modified version of Munk’s canonical sound field model. This model is used in a simulated environment with a 15-Hz source where source and receiver locations are known. The simulation demonstrates that changes in the depth and strength of the modeled sound channel axis directly result in trackable errors in range and depth as well as in reduction of the received power level. The same model is used to determine sound-speed profile using a 15-Hz signal from a 244-m explosive source detected on a 675-m vertical array at a range of 53 km in a deep water Pacific environment, characterized by a classical range-independent sound channel at 700 m. The search for the best estimated profile is conducted by varying the sound channel axis strength and depth in the modified Munk equation, while maintaining a constant sound-speed profile at great depths. For the single test case, resultant differences between the matched-field estimated and measured profiles are less than ±2 m/s; the sound channel axis depth is determined within 20 m of the measured axis depth.
Neural network feature vectors for sonar targets classifications
Authors: Svärdström Anders
Published: October 2005

This paper deals with classification of objects using active sonar and neural network classifiers. Various methods of feature extraction, i.e., transformations of the recorded data to a form better suited as inputs to the classifier, have been applied to recorded active sonar data. The well-known multilayer perceptron architecture has been used. To reduce the computational effort and the number of parameters to estimate, the number of input nodes were limited, and it has been shown that feature vectors using Walsh transform coefficients are superior to feature vectors using Fourier transform coefficients under this constraint. Particularly with low SNR, the feature vectors based on Walsh transform coefficients outperform the Fourier based vectors. Some minor effort has been expended on optimizing the neural network implementation.
Propagation in an anisotropic periodically multilayered medium
Authors: Potel Catherine , de Belleval Jean-François
Published: October 2005

An anisotropic multilayered medium is studied using the method of transfer matrices, developed by Thomson [J. Appl. Phys. 21, 89 (1950)] and Haskell [Bull. Seismol. Soc. Am. 43, 17 (1953)]. The propagation equations in each layer of the multilayered medium use the form developed by Rokhlin et al. [J. Acoust. Soc. Am. 79, 906–918 (1986); J. Appl. Phys. 59 (11), 3672–3677 (1986)]. Physical explanations are given, notably when a layer is made up of a monoclinic crystal system medium. The displacement amplitudes of the waves in one layer may be expressed as a function of those in another layer using a propagation matrix form, which is equivalent to relating the displacement stresses of a layer to those in another layer. An anisotropic periodically multilayered medium is then studied by using a propagation matrix that has particular properties: a determinant equal to one and eigenvalues corresponding to the propagation of the Floquet waves. An example of such a medium with the axis of symmetry of each layer perpendicular to the interfaces is then presented together with the associated reflection coefficients as a function of the frequency or of the incident angle.
Active control of sound radiation from a simply supported beam: Influence of bending near-field waves
Authors: Guigou C. , Fuller C. R.
Published: October 2005

Active control of sound radiation from a baffled simply supported finite beam is analytically studied. The beam is subjected to a harmonic input force and the resulting acoustic field is minimized by applying a control point force. For a single frequency, the flexural response of the beam subject to the input and control forces is expressed in terms of flexural waves of both propagating and near-field types. The optimal control force complex amplitude is derived by minimizing the acoustic radiated pressure at one point located in the far field. The far-field radiated pressure, the displacement of the vibrating beam, and the one-dimensional wave-number spectrum of the beam velocity are extensively studied. In order to further understand control mechanisms, the radiated pressure due to the flexural propagating wave and the flexural near-field wave, respectively, is investigated at the minimization point before and after the control is involved. The analysis shows that, when the control is applied, the combination of the radiated pressure due to the two different types of waves (as their associated radiation is out-of-phase) at the minimization point causes the large pressure attenuation. These results demonstrate that structural near fields are important in terms of predicting performance in active control of structurally radiated sound.
Acoustic control by wave field synthesis
Authors: Berkhout A. J. , de Vries D. , Vogel P.
Published: October 2005

The acoustics in auditoria are determined by the properties of both the direct sound and the later arriving reflections. If electroacoustic means are used to repair disturbing deficiencies in the acoustics, one has to cope with unfavorable side effects such as localization problems and artificial impressions of the reverberant field (electronic flavor). To avoid those side effects, the concept of electroacoustic wave front synthesis is introduced. The underlying theory is based on the Kirchhoff–Helmholtz integral. In this new concept the wave fields of the sound sources on stage are measured by directive microphones; next they are electronically extrapolated away from the stage, and finally they are re-emitted in the hall by one or more loudspeaker arrays. The proposed system aims at emitting wave fronts that are as close as possible to the real wave fields. Theoretically, there need not be any differences between the electronically generated wave fields and the real wave fields. By using the image source concept, reflections can be generated in the same way as direct sound.
Exact mode representation of sound propagation in a shallow-water wedge with a penetrable bottom
Authors: Chu Dezhang
Published: October 2005

A new solution for the acoustic wave propagating in a wedge-shaped shallow-water waveguide with a penetrable bottom (ρ1≠ρ2, c1≠c2) is presented. By using a special transformation of range function (Bessel function), the inherent nonseparable problem can be converted to a pseudoseparable one. The solution is exact and is expressed as a summation of wedge mode sets, i.e., each eigenvalue corresponds to a set of eigenfunctions. There are several advantages of the present method over the conventional coupling mode method: (1) since the cylindrical coordinates corresponding to wedge modes are used, the media are bounded in angular direction 0←θ←π; therefore, the mode spectrum of the exact solution only contains discrete modes. (2) The diffracted wave from wedge apex is included automatically. The contribution of the diffracted wave to the total field is important when kr≪1, where k is the wave number and r is the range from the wedge apex. (3) The mode coefficients are obtained through recursive formulas instead of solving M linear equations simultaneously, where M is the number of modes. When c1=c2, the problem becomes separable and for each eigenvalue, only the primary eigenfunction corresponding to a conventional wedge mode remains nonzero. Hence, the solution smoothly reduces to that for an isovelocity/density contrast wedge [D. Chu, J. Acoust. Soc. Am. 87, 2442–2450 (1990)]. Numerical computations are presented to show the effect of mode coupling in terms of different geometrical and physical parameters.
Simulation studies of narrow-band and cw acoustic propagation through a shallow-water internal wave
Authors: Chin-Bing Stanley A. , King David B. , McGirr Robert W.
Published: October 2005

The effects of a shallow-water, solitary internal wave on cw and narrow-band acoustic propagation have been studied using computer simulations. Numerous observations have been made of solitary internal waves in shallow water. These internal waves travel along the near-surface thermocline for some distance without loss of coherence. Due to their prevalence, they have been cited as the likely cause of the anomalous effects observed in some recent shallow-water acoustic measurements. In order to test this hypothesis, computer simulations of acoustic propagation through an internal wave have been made using an ocean-acoustic PE propagation computer model (EFEPE), fast Fourier transformations (FFTs), and beamforming algorithms. A narrow band of frequencies was used with the center frequency at 250 Hz. The resulting frequency-dependent fields were then converted into the time domain via an FFT. Beamforming algorithms were used to analyze the field structure. Examples will be shown that contrast the internal wave effects on cw propagation and on narrow-band propagation. [Work supported by ONR and NRL.]
Measurements of propagation loss in isothermal surface ducts
Authors: Cotaras F. D. , Morash P. D. , Franklin J. B.
Published: October 2005

Over the past several years, the Defence Research Establishment Atlantic has made measurements of propagation loss in surface ducts. The experiments were conducted at deep-water locations, and both the source (SUS charges) and receiver were placed in the duct. At the sites where the surface duct was well defined and constant with range, the data are in good agreement with a simple propagation-loss model. Inputs to the model include the sound absorption coefficient cited by Scheifele, Mellen, and Browning as well as the reflection-loss predictions of Brekhovskikh and Lysanov’s method of small perturbations. The sea-surface was assumed to be described by a Pierson–Moskowitz frequency spectrum.
Improvement in the shallow-water prediction of sonobuoy detection ranges for ASW aircraft using on-site acoustic measurements
Authors: Wiseman Charles
Published: October 2005

Sonobuoy detection ranges predicted at shore stations for use by antisubmarine warfare (ASW) aircraft are based on historical data and on expendable bathythermograph (XBT) data that are typically at least 6 to 12 h old. The accuracy of such predictions is questionable as shown by measurements and analysis. Prediction accuracy needs to be improved to increase the effectiveness and lower the costs of antisubmarine search and barriers using sonobuoys dropped from ASW aircraft. These predictions can be improved during the mission by measuring the on-site sound propagation loss between a specially modified air-dropped electronic sound source, similar in concept to a long-lived MK 84 SUS sound projector, and the acoustic receivers in the air-dropped sonobuoys. The derived propagation loss, used in conjunction with the XBT-based predictions, can be used to more effectively select sonobuoy depths and patterns. The existing MK 84 SUS projector could be modified to be neutrally buoyant and provide 140 ping seconds of pre-programmed transmissions over a 6 h life. The transmissions can be shaped for low probability of intercept or mimicry. Similar applications to improve sonar range prediction for surface ships are also addressed.
Ultrasonic nondestructive evaluation of thin (sub-wavelength) coatings
Authors: Kinra Vikram K. , Zhu Changyi
Published: October 2005

This paper describes a technique for ultrasonic nondestructive evaluation (NDE) of a thin coating on a thick substrate; here thin means the thickness of the coating is less than the wavelength of the ultrasonic wave used to interrogate it. A plane longitudinal wave that is normally incident upon the coating is considered. Transfer functions have been derived for both the coating-side and the substrate-side insonification. A systematic analysis of the sensitivity of the transfer functions to the thickness and wave speed has been carried out. An inverse algorithm, which utilizes the well-known Newton–Raphson method, has been developed to reconstruct the thickness and the phase velocity through a comparison of the theoretical and the measured transfer functions; fortunately, this algorithm is independent of the substrate thickness. Using this technique both the thickness and the wave speed of the coating can be extracted from the same measurement, without knowing either. The technique is fully automated and computer-controlled and can be easily used for in-situ NDE applications. The technique was used to measure the thickness and wave speed of epoxy and Plexiglas coatings (50–100 μm) on an aluminum substrate using low-frequency (10- and 20-MHz) transducers; the ratio of thickness/wavelength was about 1/3. The precision in the measurement of the thickness and the wave speed was found to be ±2 μm and ±3%, respectively.
Point force excitation of an elastic infinite circular cylinder with an embedded spherical cavity
Authors: Olsson Sune
Published: October 2005

In this paper the scattering of elastic waves in an infinite circular cylinder is considered. The elastic medium of the cylinder is assumed to be homogeneous, isotropic, and linear except for a finite inhomogeneity which, for simplicity, is chosen as a spherical cavity. By applying the null field approach (or T matrix method), the scattered field is obtained as a complicated expression containing the transition matrix of the cavity, the reflection matrix of the cylinder, and the transformation function between the spherical and cylindrical vector wave functions. Numerical results, both in the frequency and time domain, are presented.
Perception of synthetic silent-center syllables: A replication and extension
Authors: Clarke William D.
Published: October 2005

The purpose of this study was to replicate and extend the synthetic silent-center vowel perception study of Miranda and Strange [J. Acoust. Soc. Am. Suppl. 1 88, S55 (1990)]. The goal was to generate synthetic syllables that adequately captured the dynamic spectral information in syllable onsets and offsets. Natural and synthetic /dVd/ syllables were presented to subjects in two forms: full syllable and silent center. Natural silent centers were constructed ty retaining the burst and first three and final four pitch periods in order to achieve a desired vowel identification error rate of about 10%. Natural duration was not altered. From ILS analysis of the first three formants, synthetic syllables were generated with Haskins Labs SYN software synthesis. Natural and synthetic full syllable error rates were 2%. Natural silent center error rates were 11%. Synthetic silent centers were 23%, far less than the 60% reported by Miranda and Strange. Thus these synthetic syllables appear to have captured some of the dynamic spectral information in the syllable onsets and offsets. [Work supported by NIDCD.]
Developmental changes in cross-language vowel perception
Authors: Polka Linda , Werker Janet F.
Published: October 2005

There is considerable evidence for a reorganization in speech perception during infancy that reflects the influence of specific language experience. Infants of 6–8 months of age reliably discriminate certain non-native consonant contrasts that 10- to 12-month-olds fail to discriminate unless they have experience with those categories in their everyday language. This recent research also shows a decline in English infants’ discrimination of two German vowel contrasts, /y–u/ and /Y–U/, but discrimination at 6–8 months was below levels that have been observed for non-native consonant contrasts. The present experiment further investigated the timing and nature of developmental changes in cross-language vowel perception. Discrimination of German /u–y/ and /y–u/ and English /i/–/a/ was examined in English-learning infants aged 4 and 6 months using a habituation procedure. The 4-month-old infants discriminated all three contrasts, whereas 6-month-olds failed to discriminate both German vowel contrasts. The results indicate that developmental changes in discrimination of phonetic contrasts occur earlier for vowels than for consonants. Evidence for age-related changes in the internal structure of vowel categories will also be discussed.
Scattering from an elastic shell and a doubly infinite fluid–solid interface with random surface roughness
Authors: Bishop Garner C. , Smith Judy
Published: October 2005

A null field T-matrix formalism similar to that of Kristensson and Strom [J. Acoust. Soc. Am. 64, 917–936 (1978)], is used to obtain a formal solution for scattering from a stationary elastic shell immersed in a homogeneous and isotropic fluid half-space and in the vicinity of a doubly infinite fluid–solid interface with random surface roughness. The full elastic tensor boundary conditions are applied at each fluid–solid interface and equations that follow from the application of the Helmholtz–Kirchhoff integral and the null hypothesis to the various regions are used to construct the T matrix for the shell-interface system and the free-field T matrices for the elastic shell and the randomly rough fluid–solid interface. Spherical basis functions are used to construct the conventional free-field T matrix for the elastic shell. However, rectangular vector basis functions are used to construct a formal representation of the T matrix for the randomly rough fluid–solid interface. The free-field T matrices are introduced into the Helmholtz–Kirchhoff and the null field equations for the shell-interface system and it is shown that the T matrix for the system is simply related to the free-field T matrices for the shell and the randomly rough fluid–solid interface. Therefore, a perturbation theory T matrix for the randomly rough surface can be introduced in a relatively simple manner. An explicit representation for the scattered pressure field in the fluid is constructed. It is also shown that the formalism contains multiple-scattering effects between the surface and the shell and also on the rough interface.
Acoustic diffraction by multiple two-dimensional objects; its calculation using an approximate integral method
Authors: Nightingale T. R. T.
Published: October 2005

A method for determining the diffracted or scattered components of an acoustical wave by multiple two-dimensional objects is given. The method presented uses approximate boundary conditions to simplify the cumbersome set of integral equations associated with nonapproximate analytic solutions of the Helmholtz integral. The approximate boundary conditions are used to calculate the insertion loss for multiple two-dimensional objects of various sizes. The predictions are compared to measured results and limitations are discussed.
The effect of domainons on the energy band in ferroelectric 180° multilayered domain superlattice
Authors: Li Xingjiao , Wu Zhiming , Chen Jeffery , Cai Dingguo , Li Shaopin
Published: October 2005

Ferroelectric domain layer wave (FDLW) [X. Li, J. Appl. Phys. 56, 88 (1984)] would be induced by the ultrasonic wave in the ferroelectric 180° domain superlattice. There exist many new phenomena under the action of FDLW. Its characteristics sum up an elementary excitation ‘‘domainon’’ [X. Li etal., J. Phys.: Condensed Matter 2, 9577 (1990)]. It has been shown that the domainons subband can be formed by the interaction between domainons and electrons at the conductive band or holes at the valence band of ferroelectric 180° domain superlattice, in other words, under the action of the ultrasonic wave, the domainons would change the distribution of electrons or holes and affect the electric properties of ferroelectrics. In addition, the variation of the subband generated by ultrasonic wave with the vector k of FDLW is similar to the variation of the subband with periodic width of superlattice. The characteristics of the symmetry domainons and asymmetry domainons have been discussed. Further analysis above that the periodic potential fields have the symmetry vibration modes and asymmetry vibration modes corresponding to the same dispersion relation of FDLW, while the displacements of the two opposite domains are asymmetry and symmetry, respectively.
Electromyography in speech research
Authors: Oshima Kiyoshi , Harris Katherine S. , Bell-Berti Fredericka
Published: October 2005

This video demonstrates the application of electromyography (EMG) to the study of speech production. The origin of the electromyographic signal is the passage of the depolarization wave when a muscle fiber or nerve is stimulated. The particular merit of EMG in speech research is that it can provide information about the speech gesture in its natural units and that it directly reflects the motor command from the central nervous system carried by neural impulses. In other words, it is not merely a substitute for direct-viewing techniques but carries one a step farther back in the chain of speech events. Three general types of electrodes have been used in speech research: surface, needle, and hooked wire electrodes. Of these, surface and hooked wire electrodes have been the most useful for recording from the human articulatory muscles. A number of steps must be taken to deal with such signals, including rectification and integration. Applications and instrumentation are discussed, and the simultaneous recording of the EMG with other signals will be presented. [Work supported by NIH Grants DC-00121 and DC-00865 to the Haskins Labs.]