摘要:

Responses of single auditory‐nerve fibers in anesthetized cat to spoken nasal consonant–vowel syllables were recorded. Analyses in the form of spectrograms and of three‐dimensional spatial‐time and spatial‐frequency plots were made. Among other features, formant transitions are clearly represented in the fibers’ response synchronization properties. During vocalic segments, especially those in /mu/ and /ma/, at a stimulus level near 75 dB SPL, a strong dominance in the responses by frequencies near the second formant (F2) is found for most fibers whose characteristic frequencies (CFs) are at or aboveF2. In contrast, at more moderate levels, the same fibers may show response synchrony to frequencies closer to their own CFs. There are significant differences in the response properties of high and low/medium‐spontaneous‐rate fibers.

ISSN:0001-4966    

DOI:10.1121/1.395642

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

To relate level‐dependent properties of auditory‐nerve‐fiber responses to nasal consonant–vowels to the basic frequency selective and suppressive properties of the fibers, multitone complexes, with the amplitude of a single (probe) component incremented, were used as stimuli. Quantitative relations were obtained between the systematic increase of fiber synchrony to the probe tone and the decrease of synchrony to CF, as the amplitude of the probe tone was increased. When such relations are interpreted as a measure of fiber frequency selectivity based on a relative synchrony criterion, a breadth of frequency tuning is obtained, at a 70‐dB SPL multitone sound‐pressure level, which is generally broader than that of the fiber’s threshold tuning curve. Quantitative comparisons with the same fiber’s responses to the nasal speech sounds indicate that the fiber’s speech responses share some common features with its probe‐tone responses.

ISSN:0001-4966    

DOI:10.1121/1.395643

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A composite inner‐ear model, containing the middle ear, basilar membrane (BM), hair cells, and hair‐cell/nerve‐fiber synapses, is presented. The model incorporates either a linear‐BM stage or a nonlinear one. The model with the nonlinear BM generally shows a high degree of success in reproducing the qualitative aspects of experimentally recorded cat auditory‐nerve‐fiber responses to speech. In modeling fiber population responses to speech and speech in noise, it was found that the BM nonlinearity allows bands of fibers in the model to synchronize strongly to a common spectral peak in the stimulus. A cross‐channel correlation algorithm has been devised to further process the model’s population outputs. With output from the nonlinear‐BM model, the cross‐channel correlation values are appreciably reduced only at those channels whose CFs coincide with the formant frequencies. This observation also holds, to a large extent, for noisy speech.

ISSN:0001-4966    

DOI:10.1121/1.395644

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

In this article, the wave propagation in an infinite piezoelectric solid cylinder of an arbitrary cross section is studied. In the analysis, the boundary conditions are satisfied by the use of Nagaya’s Fourier expansion collocation method. The frequency equations for symmetric and antisymmetric cases are obtained and analyzed numerically for longitudinal and flexural waves for the piezoceramic material PZT‐4. The vibrations of circular and elliptical cylinders are investigated and the results are tabulated. The results obtained for a circular cross section are compared with the available results. The frequency versus the aspect ratio (the ratio of the semimajor and semiminor axes of the elliptical cylinder) is plotted and the dispersion curve is also presented.

ISSN:0001-4966    

DOI:10.1121/1.395645

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Acoustic wave scattering by spherical shells in water in the resonance region is studied. The interaction is studied classically and by the resonance scattering theory (RST). The connection between internal resonances and the Lamb waves excited in the shell is analyzed. Conditions are derived that govern the propagation of Lamb waves in a spherical shell when it is fluid‐loaded orinvacuo. These general conditions reduce to the usual conditions for Lamb waves inplates, in the large radii limit. The connection is established between the outer scattering problem and the internal vibrational problem that excites the shell resonances, and it is demonstrated that the creeping‐wave series that synthesizes the Franz waves around the shell, can be obtained quite simplywithoutthe use of the Watson–Sommerfeld Method (WSM).All that is required is suitable one‐term expansions of the denominators of the scattering amplitudes. This eliminates the need for the cumbersome excursions through the complex angular momentum plane ν of the WSM. Calculations are presented for the summed form functions of seven shells of three compositions and thicknesses over quite broad frequency bands. Subtraction of rigid or soft backgrounds permits one to draw many conclusions as to the behavior of the shell response in various spectral regions. The relative phase between the form function and the background is also displayed. This phase is helpful for the identification of actual resonances and for the choice of proper background. It is shown how the poles of the scattering amplitude in thexplane split into two subsets. One set, the Franz set, depends only on shell shape, and is related to the external Franz (creeping) waves in the water. This set does not change with varying shell thickness or composition. The other set, the Lamb set, depends only on material composition, and is related to the Lamb waves in the shell. These poles are displayed in various cases, and it is shown that for thin shells, only one family of Lamb poles (the zeroth‐order symmetric family,s0) is dominant, which explains the relatively simple structure of the form function of a thin shell. For thicker shells, many modes interact, and one is forced to go to the usual partial‐wave analysis of the RST. A very accurate picture of the scattering process taking place around and inside the shell emerges from this analysis.

ISSN:0001-4966    

DOI:10.1121/1.395646

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Detonation of explosives during rock excavation in surface mining produces both atmospherically and seismically propagating disturbances. By manipulating the difference in arrival times of the air blast and ground motion, shot‐to‐recorder distance can be determined with only one recording station. This shot‐to‐recorder distance is needed for automatic development of ground motion attenuation curves with automatic recording devices and is generally helpful in mine activity detection. With two recording stations, the location of the blast may be determined even if the stations are not time synchronized. Data from production blasting at a coal mine were evaluated to verify the method proposed herein. The blast location as determined by the difference in arrival times of the atmospherically and seismically propagating disturbances showed excellent agreement with the location of blasts as provided by field personnel. The method may be employed to detect any explosive activity that produces both types of disturbances.

ISSN:0001-4966    

DOI:10.1121/1.395647

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The existing theory of acoustic propagation through an oceanic internal wave field with a Garrett and Munk spectrum is modified and, by numerical computation, is shown to be consistent. The fractional sound speed computation is rederived to satisfy the Garrett and Munk spectrum and used to compute a stochastic simulation of the internal wave sound speed fluctuation field. The Garrett and Munk spectrum in (ω,j) space has been normalized by 4π, and the acoustic scattering is redefined to accommodate scattering from the internal wave phase fronts as in an acoustic phase grating. These modifications are then used to compute the coherent acoustic intensity by two methods: a first‐order multiple scatter approximation and a stochastic simulation. Also, the Rytov approximation is shown to be equivalent to the first‐order multiple scatter approximation in the form of the stochastic parabolic equation method in the unsaturated region. The computational results show agreement in the weak scattering region using typical deep ocean values. The stochastic simulation method is accurate in the saturated and unsaturated regions; however, the method requires long computer execution times. Phase front fragments propagating along rays with sound speeds reduced by the stochastic internal wave field are used to discuss the computational results.

ISSN:0001-4966    

DOI:10.1121/1.395648

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

An expression is derived for the acoustic field scattered by a rigid sphere in an isovelocity fluid layer overlying a horizontally stratified medium. The result, valid when multiple scattering can be neglected, is expressed in terms of normal modes and plane‐wave scattering functions. It allows simple physical interpretation and straightforward numerical implementation. Sample numerical calculations are given for two cases typical of shallow‐water environments. Generalizations to a depth‐dependent sound velocity fluid layer and to nonrigid spheres are indicated. A second derivation is given for objects of nonspherical shape in a form similar to that of the rigid sphere. Hence, if the plane‐wave scattering functions for the object are known, the scattered field in a stratified medium can be calculated.

ISSN:0001-4966    

DOI:10.1121/1.395649

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The method of physical optics is applied to treat high‐frequency acoustic scatter from Arctic ice. The development takes into account that the under‐ice surface is not statistically homogeneous, but consists of two types of ice: undeformed first year and multiyear ice, and very rough ice due to pressure ridge formation. Expressions are obtained both for the mean scattering strength and the spatial coherence of the scattered field. Measured ice statistics are used to evaluate the expressions derived for the spatial coherence and to estimate the variability of the mean backscattering strength.

ISSN:0001-4966    

DOI:10.1121/1.395650

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Due to the difficulty of direct measurement, there is a need to develop inverse techniques for remote sensing bottom geoacoustic parameters in the lowan mode measurements are extended to extract acoustic attenuation and speed in a horizontally stratified bottom in shallow water as a function of frequency and depth. The computational and experimental results show that, for a limited frequency band, we can find an equivalent depth profile of sea‐bottom acoustic attenuation with a linear frequency dependence that simulates the effect of nonlinear frequency dependence (without depth structure) on some field characteristics, such as the attenuation rate of individual mode, the frequency response of long‐range sound propagation, and the amplitude ratio of mode 2 to mode 1. However, the resultant equivalent negative gradient for the sea‐bottom attenuation is too strong to be accepted in light of available data. The conclusion is that nonlinear frequency dependence of the acoustic attenuation in the upper sedimentary layer is required to explain many aspects of shallow‐water sound propagation.

ISSN:0001-4966    

DOI:10.1121/1.395651

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP