摘要:

An analysis is made of the production of acoustic disturbances at solid‐gas and liquid‐vapor interfaces that are subject to transient thermal radiation. The interaction of radiation with phase‐exchange rate processes at the interfaces is the mechanism by which acoustic disturbances are produced. General expressions are derived for the perturbation velocity of the gas or vapor in terms of an arbitrary time‐dependent radiant heat flux. Explicit solutions are derived for the case of a stepwise pulse of radiation. Results are applied to tungsten‐oxygen, glass‐nitrogen, and mercury liquid‐vapor interfaces.

ISSN:0001-4966    

DOI:10.1121/1.1911170

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The scattering of elastic pulses by rigid obstacles of arbitrary shape is discussed in terms of an integrodifferential equation similar to Kirchhoff's equation. This approach has proved valuable in the treatment of acoustic scattering problems and the extension proposed is relatively straightforward. The advantage of this approach is that the problem can be formulated completely in terms of values of stress and strain on the scattering surface only thereby reducing the order of the problem by one spatial dimension. Field values can be obtained from the surface values by a direct quadrature if required. The simple problem of aP‐step wave reflecting from an infinite rigid plane is discussed as an example of the procedure.

ISSN:0001-4966    

DOI:10.1121/1.1911171

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Frequency equations and mode shapes are presented in analytic form for the torsional vibrations of solid prolate spheroids and thick prolate spheroidal shells. The solutions are shown to include the previously obtained solid sphere and thin prolate spheroidal shell results as limiting cases. Numerical results are presented for solid prolate spheroids.

ISSN:0001-4966    

DOI:10.1121/1.1911172

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The process of diffraction of sound waves by finite obstacles is now commonly analyzed in terms of creeping waves that encircle the scattering object azimuthally. For the example of a soft infinite circular cylinder, we have studied the scattering of pulsed sound waves, both of delta‐function and of finite‐step‐function shape (with or without harmonic modulation). We investigated the changes in pulse shape that occur as the pulse propagates over the cylinder surface. This constitutes an extension of previous work by Friedlander and by the present authors in which only the initial rise of the creeping pulses was obtained numerically, and it has been accomplished by an asymptotic expansion in the Laplace‐transform variables.

ISSN:0001-4966    

DOI:10.1121/1.1911173

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

This paper presents the detailed mathematical properties and the ray‐theory ranges, intensities, and travel times of the five‐parameter Epstein profile with the parameters assuming all values capable of producing real velocities. Although examples represent the underwater‐sound situation, results apply to any ray theory. The wealth of profile forms produces special cases requiring intricate analysis, but leads to more complete understanding of field theory. Analyses of rays that become horizontal at velocity extrema show little dependence on profile symmetry for the case of a velocity maximum, but a marked dependence for the case of a velocity minimum. This last is a point of significance apparently neglected in the literature covering ray‐theory channels. Very steep, channeled rays, which become horizontal at very high (infinite) velocities, are shown to have a loop range πC(dZ/dC), where the velocity‐slope product is evaluated as a limit at the infinite velocity. This expression, valid for profiles other than the Epstein profile, was suggested by examination of the hyperbolic cosine profile, which is a degenerate case of the Epstein profile.

ISSN:0001-4966    

DOI:10.1121/1.1911174

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

This study is concerned with optimum waveforms for correlation detection in the sonar environment. The selection of optimum waveforms for combating random multipath under noise‐limited conditions was considered previously [T. G. Kincaid, J. Acoust. Soc. Am.43, 258–268 (1968)]. In this paper, the same problem is considered under reverberation‐limited conditions. The optimum waveforms are required to maximize the ratio of expected signal to expected reverberation plus noise under a fixed‐energy constraint. Necessary and sufficient conditions for the optimum waveforms are derived. As under noise‐limited conditions, it has only been possible to develop a technique for finding waveforms that satisfy a necessary condition. However, it is conjectured that this technique produces optimum waveforms. Conjectured optimum waveforms are found for selected examples, and their performance is compared to that of two conventional (CW and chirp) waveforms.

ISSN:0001-4966    

DOI:10.1121/1.1911175

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Many studies have been made of man's ability to localize various types of sounds under various acoustic conditions. Of particular interest in loudspeaker reception is the ability to localize transient‐type signals that originate at or near the intersection of the horizontal and median planes, i.e., in the region directly in front of the listener. The present study explores this ability for high quality speech signals in noise‐free, anechoic space. It was found that, under such test conditions, the average error of lateral or angular localization was 1.5°. In addition, an average individual bias of 1.1° and a group bias of less than ±0.1° were also found. When the speech signals were presented over a wide range of levels from a source located among similar units displayed at various angles and distances from the observer, average angular shifts as large as 5° were observed in the apparent lateral position of the source.

ISSN:0001-4966    

DOI:10.1121/1.1911176

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Auditory‐flutter fusion (AFF) threshold measurements were made for pure tones and white noise by varying the rise and decay time. The tests were conducted with trained, normal‐hearing subjects and also those with pathological ears. Off time was the major factor in determining the AFF threshold. The off time required to obtain AFF threshold was dependent upon the rise and decay time and followed a definite pattern referred to in the derived equation. There was no relationship between on time and AFF threshold. Other variables such as testing intensity level, interruption rate, and stimulus components did not provide any statistically significant alteration of AFF threshold. AFF thresholds were similar for both normals and pathologicals with and without abnormal adaptation.

ISSN:0001-4966    

DOI:10.1121/1.1911177

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Experiments are described in which the accuracy of the perceived lateral position of a signal against a continuous background of masking noise is determined. Both signal and masker consisted of octave bands of thermal noise, with the same center frequency of 500 Hz. The signal‐to‐noise ratio and signal duration served as parameters. The results can be understood on a statistical basis, the random fluctuations of nerve impulses playing an important rôle. The fluctuations due to “internal” noise are found to have a standard deviation of about 80 μsec. It appeared that, as a result of the increase of the sound‐pressure level, the onset part of the signal contributes more to the lateral position perceived than the ongoing part does. The relation to the precedence effect is discussed. The statistical procedure underlying the accuracy of the lateral position perceived suggests an approach to the binaural masking level difference effect based on a masking pattern in the binaural‐hearing mechanism.

ISSN:0001-4966    

DOI:10.1121/1.1911178

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A series of two‐alternative forced‐choice experiments showed that for short durations, the detection of a tonal signal in noise when the two are gated synchronously is superior to the detection of the signal in a background of continuous noise. The experiments also showed that for gated signal and noise, there is a steady improvement in detection as the duration is shortened, provided that highly practiced observers are employed in the task. Naïve observers exhibit a similar trend, but their performance drops at the short durations (5 and 10 msec) where the listening task becomes very difficult.

ISSN:0001-4966    

DOI:10.1121/1.1911179

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP