摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.420115

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

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 athttp://www.uspto.gov.

ISSN:0001-4966    

DOI:10.1121/1.419776

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

In this paper, a detailed acoustic study of foreign accent is proposed using temporal features, intonation patterns, and frequency characteristics in American English. Using a database which consists of words uttered in isolation, temporal features such as voice onset time, word-final stop closure duration, and characteristics of duration are investigated. Accent differences for native-produced versus Mandarin, German, and Turkish accented English utterances are analyzed. Of the dimensions considered, the most important accent relayer is found to be word-final stop closure duration. Mandarin accented English utterances show significant differences in terms of this feature when compared to native speaker utterances. In addition, the intonation characteristics across a set of foreign accents in American English is investigated. It is shown that Mandarin speaker utterances possess a larger negative continuative intonation slope than native speaker utterances, and German speaker utterances had a more positive intonation slope when compared to native speaker utterances. Finally, a detailed frequency analysis of foreign accented speech is conducted. It is shown that the midfrequency range (1500–2500 Hz) is the most sensitive frequency band to non-native speaker pronunciation variations. Based on this knowledge a new frequency scale for the calculation of cepstrum coefficients is formulated which is shown to outperform the Mel-scale in terms of its ability to classify accent automatically among four accent classes.

ISSN:0001-4966    

DOI:10.1121/1.419608

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The problem of scattering of an obliquely incident plane acoustic wave from an infinite solid elastic clad rod is formulated. Numerical calculations show the effects of the variations of the cladding thickness on both the backscattered pressure spectrum and individual normal modes. It is shown that various resonance frequencies have different levels of sensitivity to variations of the cladding thickness. Experimental measurements are also performed at both normal and oblique incident angles on a copper-clad aluminum rod; good agreement is observed between the calculated and the measured results. These results demonstrate the potential of acoustic resonance scattering procedures for application in nondestructive evaluation (NDE) of clad rods.

ISSN:0001-4966    

DOI:10.1121/1.419764

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The predictions of resonance frequencies for elongated elastic cylinders and spheroids, based on various methods of approach, were discussed in a number of papers in recent years. In the present study, the regions of applicability of the phase matching method for surface waves and of the longitudinal bar wave approximation are examined by comparing the predicted results with the results ofT-matrix calculations or with the results of scattering experiments.

ISSN:0001-4966    

DOI:10.1121/1.419723

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

Attenborough has recently proposed [J. Acoust. Soc. Am.98, 1717–1722 (1995)] that the effects of surface roughness on an otherwise flat surface of finite acoustic admittance can be modeled as a smooth flat surface with an effective acoustic admittanceβ*.This effective admittance is determined by the normalized admittanceβsand wave numberksof the original smooth surface, as well as a surface roughness parameterσν.Attenborough tested his theory by conducting excess attenuation measurements over plywood and Styrofoam surfaces with two-dimensional roughness elements. Specifically, he investigated the interference pattern between the direct and reflected signals over both smooth and rough surfaces. Experiments are conducted here with three-dimensional roughness elements at grazing incidence. Such a configuration is typical for outdoor sound propagation problems. The results presented here generally confirm Attenborough’s model and open up the analogy to a broader class of problems. It was also found that placing the effective admittance plane at the top of the roughness elements rather than at the bottom yielded slightly better results for the higher acoustic frequencies investigated.

ISSN:0001-4966    

DOI:10.1121/1.419728

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The acoustic backscattering behavior of both nonmetallic (glass) and metallic (steel) cubes has been investigated over a wide frequency range where elastic resonances are important in determining the acoustic response of the cubes. A laboratory system incorporating a parametric array was used to make measurements between 20 and 200 kHz using cubes of side(l)20 mm, and a combined finite element/boundary element code was used to numerically model scattering by the cubes. The frequency range covered corresponds tokavalues up to 10, wherea=l(3/4π)1/3is a characteristic dimension of the cube. Results are presented for three scattering geometries involving incidence on to a face, an edge, and a corner. The backscattered form function differs greatly for the different geometries and is seen to depart significantly from that of a rigid cube whenka>5due to the elastic resonances of the cube. The resonance contributions are clearly seen when the rigid background is subtracted from the elastic predictions.

ISSN:0001-4966    

DOI:10.1121/1.419734

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A crucial ingredient in the formulation of boundary-value problems for acoustic scattering of time-harmonic waves is the radiation condition. This is well understood when the scatterer is a bounded obstacle. For plane-wave scattering by an infinite, rough, impenetrable surfaceS,the physics of the problem suggests that all scattered waves must travel away from (or along) the surface. This condition is used, together with Green’s theorem and the free-space Green’s function, to derive boundary integral equations overS.This requires careful consideration of certain integrals over a large semicircle of radiusr; it is known that these integrals vanish asr→∞if the scattered field satisfies the Sommerfeld radiation condition, but that is not the case here—reflected plane waves must be present. The integral equations obtained are Helmholtz integral equations; they must be modified for grazing incident waves. As such integral equations are often claimed to be exact, and are often used to generate benchmark numerical solutions, it seems worthwhile to establish their validity or otherwise.

ISSN:0001-4966    

DOI:10.1121/1.419714

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

A method is presented to calculate the near- and far-field transient radiation of acoustical transducers using low sampling frequencies. The method is based on the classical impulse response approach and on the fact that in practical use the spectrum of the excitation function of a transducer is band limited. This makes it possible to use a smoothed version of the impulse response function. A simple expression to calculate this smoothed function, for a rectangular or circular transducer, is derived. The proposed solution allows accurate computation of pressure fields and backscatter signals, while avoiding high sampling frequencies in the far field of the transducers. Several examples illustrate the accuracy of this new solution and its use for spectral analysis of simulated reflected signals.

ISSN:0001-4966    

DOI:10.1121/1.419715

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP

摘要:

The scattering of a plane sound wave normally incident on an absorbing elastic cylinder immersed in water is investigated theoretically. Because of the loss of acoustic energy due to absorption, the unitarity condition of the usualSmatrix arising from the classical resonant scattering theory fails. However, it is shown that this unitarity condition can still be met by constructing a newSmatrix which is nondiagonal. This construction is analogous to the multichannel scattering theory of particle physics. Computations are performed considering an absorbing elastic cylinder in order to check the validity of the theory.

ISSN:0001-4966    

DOI:10.1121/1.419716

出版商:Acoustical Society of America    

年代:1997

数据来源: AIP