摘要:

Fast field computations without range dependence are based on computing the Hankel transform of the Green's function of the separated depth‐dependent ordinary differential equation. As usual, the required Green's function is expressed in terms of two solutions of the homogeneous differential equation, the first satisfying the boundary condition at the surface of the ocean, the second satisfying the boundary condition at the bottom of the ocean, and the Wronskian of these two functions. In our approach, one solution is given in terms of one transmutation that preserves thesurfaceboundary condition, and the other is given in terms of adifferenttransmutation that preserves thebottomboundary condition. Once the two different transmutation kernels are found, they are applied to trigometric functions that satisfy the respective boundary conditions, and the Green's function is numerically computed. A fast Hankel transform (the usual fast Fourier transform approximation was used) completes the calculation of the field versus range.

ISSN:0001-4966    

DOI:10.1121/1.2024096

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Several single number ratings, including STC, for rating the sound insulation properties of walls were correlated with the A‐weighted sound reductions of a group of gypsum board partitions for several types of sound source. None of the ratings fared well for the broad range of sound types. It is shown that a single rating method cannot deal with all sound sources. Two new ratings are proposed to supplement STC for coverage of indoor and outdoor noise reduction.

ISSN:0001-4966    

DOI:10.1121/1.2024105

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

At previous meetings of the Acoustical Society of America [L. H. Green, D. H. Trivett, and L. Flax, J. Acoust. Soc. Am. Suppl. 177, S79 (1985)], it was demonstrated that, for the analysis of the elastic excitations in the acoustic scattering from elastic targets, the proper background to subtract is a rigid background. This choice was utilized to analyze the low‐frequency scattering from spherical and infinite cylindrical shells over a broad range of frequencies and shell thicknesses. However, in a recent paper on the acoustic scattering from elastic spheroidal solids [M. F. Werby and G. J. Tango, J. Acoust. Soc. Am.79, 1260–1268 (1986)], it is concluded that a rigid background is inappropriate for elastic targets that have either low shear speeds or low densities. A complete reexamination of the scattering from elastic solids is presented to demonstrate that the rigid background is the appropriate choice in this case, too. In the course of this analysis, it is also demonstrated that Werby and Tungo have misinterpreted the nature of the elastic response of the scatterer.

ISSN:0001-4966    

DOI:10.1121/1.2024108

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A method employing boundary and finite element approaches as well as model analysis is used to study the scattering of acoustic waves by a finite cylindrical shell immersed in water. The cylindrical shell contains a mixture of wax and colophony and thus the elastic wave propagation in this mixture is also considered. The computed frequency response and direction pattern of the backscattering target strength show excellent agreement with measurements.

ISSN:0001-4966    

DOI:10.1121/1.2024112

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

In the past 15 years, research on the perception of spoken vowels has given rise to new conceptions of vowels as articulatory, acoustic, and perceptual events. This paper traces the evolution of vowel theory starting from “simple” target models in which vowels were characterized articulatorily as static vocal tract shapes and acoustically as points in anF1/F2 vowel space. Within this conceptual framework, two major problems in perception to be accounted for were the Speaker Normalization problem and the Target Undershoot problem. Theoretical developments have taken two directions: (1) “Elaborated” target theories have been hypothesized which account primarily for perceivers' solution of the Speaker Normalization problem; (2) dynamic specification models have been offered (a) to deal with the Target Undershoot problem and (b) to characterize the perceptual significance of vowel diphthongization. Findings of perceptual studies are summarized that motivate these theoretical developments and a characterization is offered of vowels as dynamic gestures giving rise to temporally distributed acoustic information that perceivers utilize in identifying coarticulated vowels. [Research supported by NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2024118

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The contribution of extraneous components to vowelF1 estimation was investigated by constructing a continuum perceived as changing from /ɪ/ to /ε/ asF1 was varied. The phoneme boundary location is a measure of the perceivedF1, and hence of the influence of the extraneous component. Adding an extraneous component whose frequency is an integral multiple ofF0/2 gives a complex consisting only of components harmonically related toF0/2. This component may thereby be incorporated by acting as a “false harmonic.” Adding a false harmonic on the lower skirt ofF1, at a level above the vowel spectral envelope, shifts the phoneme boundary upwards. However, adding a component at any other frequency in this region has a similar effect. The effect of further adding several false harmonics remote in frequency fromF1, at levels equal to the spectral envelope of the vowel, is currently being investigated. Preliminary results suggest that adding these components increases the incorporation of the component added in theF1 region, but only if that component frequency is an integral multiple ofF0/2. [Work supported by the SERC and the MRC, U.K.]

ISSN:0001-4966    

DOI:10.1121/1.2024122

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

It has generally been assumed at least since the time of the comprehensive study by Peterson and Barney [J. Acoust. Soc. Am.24, 175–184 (1952)] that the formant locations in vowel spectra are the most significant cues to vowel identity. In this experiment vowel spectra were represented by two methods: (A) by the locations of the first three formants, and (B) by the overall smoothed spectral shape in terms of a discrete cosine transform of the power spectra. Stimuli consisted of four repetitions of the widely separated vowels /u/, /i/, /a/, spoken by each of 12 female and 12 male speakers (4⋅24⋅3 = 288 stimuli total). For each of the two spectral encoding methods, A and B, the vowel data were projected to a three‐dimensional space such that the vowel categories would be well separated and the vowels within each category well clustered [S. A. Zahorian and A. J. Jagharghi, J. Acoust. Soc. Am. Suppl. 179, S8 (1986)]. Significantly better clustering was obtained with method B, based on overall spectral shape, than for method A, based only on the first three formant frequencies. Since these results are not based on perceptual experiments, no direct conclusion can be drawn regarding the perceptual importance of spectral peaks versus overall spectral shape for human perception of vowels. However, the results do indicate that automatic machine identification of vowels can be improved by parameterizing the overall spectral shape rather than only the spectral peaks.

ISSN:0001-4966    

DOI:10.1121/1.2024128

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Some preliminary efforts are reported at speaker normalization based on the assumption that listeners are tacitly aware (a) that they are listening to an instrument (the human vocal tract) which when uniform (unconstricted) should have resonances whose lowest frequencies are spaced according to the ratios 1:3:5:7, etc., (b) that the exact frequencies of these resonances depend on the length of the vocal tract, and (c) that what is relevant in resonances from a nonuniform tract is the ratio of these lowest resonances to their uniform value. There are probably several cues the listener could use to estimate the size of the speaker; for starters, we use the mean (long‐term)F4. The reference resonances forF1r,F2r,F3r, i.e., those from the “uniform” tract, are 1/7, 3/7, and 5/7, respectively, of meanF4. The normalization consists in converting measured formant frequencies,F1m, etc., into the ratios of logF1m/logF1r. The results of applying this normalization to the entire voiced portion of vowels in a variety of CVC syllables is reported. [Work supported by a Sloan grant to Berkeley Cognitive Science Program.]

ISSN:0001-4966    

DOI:10.1121/1.2024132

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

It is usual in the development of rough interface models to limit theory to two‐dimensional models or to ignore shadowing and penetration into the surface as well as surface gradient terms that arise in the formal derivation of the equations. The secood‐order term has recently been examined to determine its importance in scattering from rough interfaces. The purpose of this study is to examine the effects of (a) shadowing, (b) penetration, and (c) surface gradient terms on the overall calculation of some representative surfaces. Moreover, a full three‐dimensional model can allow for out‐of‐plane scatter, and this effect will also be examined. The method of treatment of penetration into the surface is via a local reflection coefficient. Preliminary results show that the majority of these effects are most important in backscatter, where they tend to enhance the magnitude relative to the forward direction.

ISSN:0001-4966    

DOI:10.1121/1.2024141

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

In this paper an approximation for fourth moment and second moment (two‐frequency) path integrals is presented. The approximation is similar in spirit and form to an approximation recently developed by Uscinskiet al.[B. J. Uscinski, C. Macaskill, and M. Spivak, J. Sound Vib.106, 509–528 (1986)]. However, the present approximation has the advantage that, for the cross‐frequency intensity, it factorizes to products of the cross‐frequency coherence for long ranges when the latter is calculated in the same approximation. In addition, it is easily demonstrated that the present approximation is the second of a sequence of approximations that will converge to the exact path integral. The idea of the approximation is to replace paths appearing in phase structure functions by “classical” paths plus a number times the Green's function for the spreading or Jacobi equation. The calculation then reduces to a phase screen calculation, with the coefficient of the Green's function appearing as the position at which a ray crosses the screen.

ISSN:0001-4966    

DOI:10.1121/1.2024146

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP