Volume 103, Issue 6, June 1998
- acoustical news—usa
- acoustical news—international
- book reviews
- reviews of acoustical patents
- selected research article 
- general linear acoustics 
- nonlinear acoustics, macrosonics 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- acoustical measurements and instrumentation 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- music and musical instruments 
- bioacoustics 
- letters to the editor
Index of content:
- REVIEWS OF ACOUSTICAL PATENTS
103(1998); http://dx.doi.org/10.1121/1.422995View Description Hide Description
The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet at http://www.uspto.gov.
- SELECTED RESEARCH ARTICLE 
103(1998); http://dx.doi.org/10.1121/1.423072View Description Hide Description
The precedence effect (PE) is a perceptual phenomenon that reflects listeners’ ability to suppress echoes in reverberant environments. The PE is not present at birth and appears only several months postnatal. Recent physiological studies have demonstrated correlates of the PE in the central nucleus of the inferior colliculus (ICC) of adult animals. The present study extended the same techniques to search for similar correlates in the ICC of kittens during the first postnatal month. Stimuli consisted of pairs of clicks or noise bursts presented from different locations in free field or with different inter-aural differences in time (ITD) under headphones, with an inter-stimulus-delay (ISD) between their onsets. Results suggest that a physiological correlate of the PE, i.e. suppression of responses to the second source, is present as early as 8 days postnatal, and occurs at similar ISDs to those recorded in adult cats. Suppression in kitten neurons varies with stimulus level, duration, and azimuthal position, in a similar manner to that in adult neurons. The age at which correlates of the PE in the kitten can be found precedes the age at which kittens can localize sound sources effectively, and presumably before the age at which they would demonstrate the PE behaviorally. Thus, the neural mechanisms that might be involved in the first stages of processing PE stimuli may be in place well before the behavioral correlate develops.
103(1998); http://dx.doi.org/10.1121/1.423073View Description Hide Description
Recent studies have shown that when phonating subjects hear their voice pitch feedback shift upward or downward, they respond with a change in voice fundamental frequency output. Three experiments were performed to improve our understanding of this response and to explore the effects of different stimulus variables on voice responses to pitch-shift stimuli. In experiment 1, it was found that neither the absolute level of feedback intensity nor the presence of pink masking noise significantly affect magnitude or latency of the voice response. In experiment 2, changes in stimulus magnitude led to no systematic differences in response magnitudes or latencies. However, as stimulus magnitude was increased from 25 to 300 cents, the proportion of responses that changed in the direction opposite that of the stimulus (“opposing” response) decreased. A corresponding increase was observed in the proportion of same direction responses (“following” response). In experiment 3, increases in pitch-shift stimulus durations from 20 to 100 ms led to no differences in the response. Durations between 100 and 500 ms led to longer duration voice responses with greater response magnitude, and suggested the existence of a second response with a longer latency than the first.
- GENERAL LINEAR ACOUSTICS 
103(1998); http://dx.doi.org/10.1121/1.423074View Description Hide Description
Many geophysical applications of the array sonic measurements require the knowledge of the true source-time function. Recovery of the source-time function from the borehole sonic P head waves is different from the source inversion problem in explorationseismology. The difficulty in the inversion of borehole sonic measurements arises due to the inexact knowledge of the impulse response, e.g., the inability to model the whole problem including the tool body and transducers. The random noise often encountered in seismic signals is not the key obstacle here. The inverse source problem is ill posed due to the interference of P head-wave multiples. Using waveforms from a laboratory scale model we have applied two deconvolution methods, one using a Wiener filter and the other the time-domain least-squares method. As expected, without constraints on the solutions, one cannot recover a satisfactory source-time function. An unconventional smoothness constraint is applied in the source spectrum (instead of the usual smoothness in the time-domain signals), which corresponds to a finite-duration pulse in the time domain (instead of the usual band-limited spectrum). This technique is thus called the “duration-limited” inversion. The inverted results, obtained by Wiener filtering combined with this “duration limiting” process and multichannel stacking, agree well with an independent free-field measurement. Furthermore, reconstructed receiver waveforms using the inverted source function match the measured ones. The inversion procedure is robust and potentially useful for field measurements.
103(1998); http://dx.doi.org/10.1121/1.423033View Description Hide Description
A procedure for the measurement of intrinsic scattering object properties is presented and used to obtain illustrative results. The procedure is based on the measurement of the scattered acoustic field as a function of scattering angle and frequency. Measurements are normalized using analytically determined expressions for emitter and detector beams resulting from a combination of unfocused linear elements arranged in a circular configuration. The spatialeffects of finite emitter pulse length and detector gate length are represented by a convolution formula valid for narrow-band transmitted signals and long receiver gates. The normalization includes correction for target absorption as well as measurement of the directly transmitted acoustic power in the free field and yields the average differential scattering cross section per unit volume. Under the Born approximation, this quantity is directly proportional to the spatial-frequency spectrum of the scattering medium inhomogeneities. Measured results are reported for two phantoms consisting of glass microspheres embedded in a weakly absorbing agar background medium. For the phantoms employed, scatteringeffects, rather than increased absorption, are shown to account for most of the difference in transmission loss between pure agar and agar with glass spheres. The measured differential scattering cross sections are compared with theoretical cross sections for distributions of glass spheres measured experimentally. The measured values show good relative agreement with theory for varying angle, frequency, and phantom properties. The results are interpreted in terms of wave space resolution and the potential for tissue characterization using similar fixed transducer configurations.
103(1998); http://dx.doi.org/10.1121/1.423034View Description Hide Description
When waves propagate through a medium with smooth velocity perturbations the propagation of wavefronts is determined by the eikonal equation. Here the propagation of wavefronts through a medium with small-scale velocity perturbations is analyzed using the method of strained coordinates. A partial differential equation for the first-order perturbation of wavefronts is derived that includes frequency-dependent wave propagation effects. It is shown that for the special case of the scalar Helmholtz equation with a homogeneous reference medium this leads to the same perturbation of wavefronts as obtained from the Rytov approximation. However, the method presented here can possibly be generalized to more complex wave propagation problems where the Rytov approximation cannot be used, such as the propagation of vector waves.
Various loss factors of a master harmonic oscillator coupled to a number of satellite harmonic oscillators103(1998); http://dx.doi.org/10.1121/1.423035View Description Hide Description
Three loss factors are defined for a master harmonic oscillator (HO); the I-loss factor, the U-loss factor, and the effective loss factor. A conductance (β) is conventionally defined as the ratio of the power imparted to a dynamic system by an external drive to the stored energy that this input power generates. The conductance (β) is related to the loss factor (η) by the frequency (ω); In light of this definition, it is shown that all three loss factors are identical for an isolated master HO at resonance. Differences arise among these loss factors when the master HO is coupled to satellite harmonic oscillators (HO’s). The first two loss factors retain their definitive format in the sense that the stored energy is reckoned only in the master HO; the energy stored in the coupled satellite HO’s and in the couplings is discounted. The effective loss factor, on the other hand, is defined by accounting for the total stored energy that the external drive applied to the master HO generates in the complex. The complex here is composed of the master HO, the satellite HO’s, and the in situ couplings. In those situations in which the portion of the total energy stored in the satellite HO’s and in the couplings substantially exceeds the stored energy in the master HO, the I-loss factor and the U-loss factor may substantially exaggerate the true loss factor of the coupled master HO. Situations of this type are illustrated by data obtained in computational experiments, and it is argued that the true loss factor of the master HO in the complex as a whole is the effective loss factor.
- NONLINEAR ACOUSTICS, MACROSONICS 
103(1998); http://dx.doi.org/10.1121/1.423075View Description Hide Description
Propagation resulting from finite pulselength stresses applied at one end of a hysteretic material is analyzed using a propagation model containing a double modulus, or two-signal-speed, approximation of the stress-strain relation. The local signal speed is determined at any instant by both the value of stress and the sign of its time derivative (i.e., time-local history). It is shown that far-field waveforms do not determine unique source profiles. The propagation mechanism responsible for the ambiguity in source identification is common to broad classes of both local and global hysteretic stress-strain operators. Consequently, one may expect that it is typical of hysteretic materials that remote sources are not uniquely determined by observed waveforms.
New evolution equations for the nonlinear surface acoustic waves on an elastic solid of general anisotropy103(1998); http://dx.doi.org/10.1121/1.423036View Description Hide Description
New evolution equations for the nonlinear surface acoustic waves in anisotropic media are derived in the frame of the second-order elasticity theory. The proposed theory explicitly accounts for the possible significant difference of the depth structure of the nonlinear surface acoustic waves with the depth structure of the linear surface acoustic waves. The derived equations reduce to the form, recently obtained for the nonlinear Rayleigh surface acoustic waves in isotropic solids, when two partial waves (contributing to the surface acoustic wave propagating along a crystal axis in the basal plane of a cubic crystal) exhibit purely exponential decay in depth.
Dispersion of nonlinearity, nonlinear dispersion, and absorption of sound in micro-inhomogeneous materials103(1998); http://dx.doi.org/10.1121/1.423037View Description Hide Description
New evolution equations for nonlinear acousticwaves in micro-inhomogeneous media, which take into account relaxation processes, are derived. The proposed theory provides the description of such physical effects as frequency-dependent nonlinear absorption of sound, nonlinearity of its velocity dispersion, and dispersion of the nonlinear acoustic parameters of micro-inhomogeneous materials. The theory predicts that, depending on the ratio of the characteristic relaxation time to the wave period, nonlinearity can grow or diminish with increasing frequency, while an increase in wave amplitude can lead to a rise or fall of the propagation velocity. In the limiting cases where the relaxation processes are instantaneous or quasi-frozen, analytical solutions of the nonlinear equations are found and analyzed.
Experimental detection of a subharmonic route to chaos in acoustic cavitation through the tuning of a piezoelectric cavity103(1998); http://dx.doi.org/10.1121/1.423038View Description Hide Description
Experimental observation is reported of a subharmonic route to chaos through the tuning of a piezoelectriccavity. The emission spectrum of bubbles generated in a liquid contained in the cavity through the application of a pressureultrasonic field of constant frequency is analyzed. The cavity height is used as control parameter to vary the resonance frequency of the cavity. In the emission spectrum of the bubbles subharmonics of the excitation frequency are observed. This phenomenon is identified as a period-doubling bifurcation and is explained on the basis of a simple model of resonance in the cavity. The appearance of subharmonics is highly sensitive to changes in the cavity height.
103(1998); http://dx.doi.org/10.1121/1.423039View Description Hide Description
Near-field acoustic levitation is successfully applied to transport objects without contact. Planar objects having a weight greater than 10 kgf can be stably levitated near a vibrating plate. An experimental apparatus has been fabricated to measure the transportation speed and transient characteristics.
- UNDERWATER SOUND 
103(1998); http://dx.doi.org/10.1121/1.423040View Description Hide Description
Recently a time-reversal mirror (or phase-conjugate array) was demonstrated experimentally in the ocean that spatially and temporally refocused an incident acoustic field back to the original position of the probe source [Kuperman et al., J. Acoust. Soc. Am. 103, 25–40 (1998)]. Here this waveguide time-reversal mirror technique is extended to refocus at ranges other than that of the probe source. This procedure is based on the acoustic-field invariant property in the coordinates of frequency and range in an oceanic waveguide [Brekhovskikh and Lysanov, Fundamentals of Ocean Acoustics , 2nd ed. (Springer-Verlag, Berlin, 1991), pp. 139–145]. Simulations are combined with experimental data to verify this technique.
103(1998); http://dx.doi.org/10.1121/1.423041View Description Hide Description
Forward and bistatic scattering of sound by individual fish at frequencies of 120 and 200 kHz have recently been measured in the laboratory following an earlier experiment conducted at acoustic frequency of 38 kHz by Ding [J. Acoust. Soc. Am. 101, 3398–3404 (1997)]. The results of forward-scattering strength obtained here, combined with those obtained in Ding, provide an empirical dependence of forward-scattering strength on acoustic frequency. It is observed that the forward-scattering strength increases rapidly with frequency and is much stronger than the backscattering strength. Scattering patterns, or scattering strength as a function of receiving angle, have also been measured for the first time in this new experiment. These results are currently being examined using theoretical models taking appropriate account of effects of both fish flesh and swimbladder.
A viscous-elastic swimbladder model for describing enhanced-frequency resonance scattering from fish103(1998); http://dx.doi.org/10.1121/1.423076View Description Hide Description
Acoustic scattering from many species of fish is strongly increased by the resonance response of the swimbladder. This gas-filled, elastic-walled internal sac may have several functions, including hearing and buoyancy. A complete physical description of the response must include the swimbladder wall, the surrounding flesh, and the gas enclosed. This work presents a new mathematical/physical model to describe resonancescattering from swimbladder fish. The model consists of a spherical air bubble enclosed, first, by an elastic shell (representing the swimbladder wall), and then by a viscous shell (representing the surrounding fish flesh). The rigidity of the inner shell increases the monopole resonance frequency of the bubble. The viscosity of the outer shell causes the resonance to be damped. By allowing these factors to vary within physically reasonable bounds, the new model has been used to explain the experimentally measuredresonance frequencies and damping of swimbladder resonances in Atlantic cod. The model provides insights into the physiological mechanisms by which fish may actively control the resonance frequencies of their swimbladders to improve hearing, and how this control can be lost under varying water pressure conditions. The impact of this issue on fisheries survey procedures is discussed.
Modeling the propagation from a horizontally directed high-frequency source in shallow water in the presence of bubble clouds and sea surface roughness103(1998); http://dx.doi.org/10.1121/1.423042View Description Hide Description
Among the many factors affecting the propagation of sound in shallow water, surface-generated microbubbles have remained virtually unexplored. The collection of microbubbles, bubbles which usually do not result in a uniform layer, presents a complex structure that varies not only in depth but also in range, and can be characterized as a collage of bubble clouds. A numerical procedure is developed in which the bubble clouds are modeled following a classification scheme proposed by Monahan [Natural Physical Sources of Underwater Sound, edited by B. V. R. Kerman (Kluwer Academic, Dordrecht, 1993), pp. 503–517]. An effective complex index of refraction of the bubble mixture is calculated for each point of the resulting range-dependent environment. The combined effect that the sea surface roughness and the bubbly environment have on forward propagation is then modeled through a high fidelity model [Norton et al., J. Acoust. Soc. Am. 97, 2173–2180 (1995)] which combines a finite element Parabolic Equation model with conformal mapping to handle surface roughness. The case of a horizontally directed source, operating at 20 kHz for a single realization of a shallow water environment is analyzed in detail. The presence of the bubble clouds severely affects the amplitude near the surface, but their influence rapidly diminishes in depth. For the case considered, the surface roughness, which has little effect on the transmission loss of the propagating field, is, however, responsible for interference effects of the forward field observed throughout the water column, while ignoring the rough surface and bubble clouds leads to a 12–15 dB error in the acoustic field near the surface, at a range of 150 m. To assume a uniformly stratified (range independent) bubble layer results in large errors near the surface at the location of the high void fraction packets, but is an acceptable approximation away from these features.