摘要:

The nonlinear interaction of two collinear ultrasonic beams in the presence of turbulence in water has been investigated. The transmitting unit was driven continuously at 3 and 5 MHz. A 1‐in, diameter water jet (20 ft/s) was located with nozzle 75 cm from the beam path which intersects the flow at 90° and originates 40 cm from it. Forward scattering angles were measured in the plane of the jet and sender by a 2‐MHz receiver located 185 cm from the interaction region. The energy spectrum of the turbulence had frequency components in the range of several Hertz to 2 kHz. In the presence of turbulence the difference frequency was broadened by sidebands up to +1 kHz from the center frequency for scattering results taken in the angular range −30° to +30°. The received spectrum was asymmetric relative to the center frequency. Comparisons are made between the spectral broadening of a primary 2‐MHz signal and the broadening associated with a difference frequency component (2 MHz) that exists due to the mechanisms of the parametric array. These results are an extension of earlier experiments of the authors on the scattering of sound by sound in the presence of turbulence for a crossed‐beam arrangement. [J. Acoust. Soc. Am.64, S14 (A) (1978)] [Work supported by the Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.2017523

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

In this paper numerical solutions of the Zabolotskaya, Khokhlov, Kuznetsov (i.e., ZKK) second‐order paraxial wave equation are used to illustrate the concept of “transverse amplitude diffusion” [G. D. Malyuzhinets, Soviet Phys. Uspekhi69, 749–758 (1959)] via the changing field structure of a diffraction‐limited parametric acoustic array. In order to establish confidence in the numerical procedure, computed solutions are first compared with analytically derived weak finite‐amplitude solutions. The amplitude‐dependent directivity of parametric arrays formed by quasisaturated and saturated primary waves is then examined by considering (i) the effect of intensity‐induced mutual coupling between adjacent ray tubes; (ii) its effect on the range‐dependent ‘diffraction’ patterns of individual spectral components; and (iii) its effect on the time waveform. Throughout the review results will be displayed by means of three‐dimensional computer graphic projections.

ISSN:0001-4966    

DOI:10.1121/1.2017524

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The energy conservation equations due to Westervelt [Proc. 3rd. Int. Congr. Acoustics, edited by L. Cremer (Elsevier, Amsterdam, 1960), p. 316] are used to show that saturation effects in a finite amplitude wave can in principle be suppressed, if the attenuation coefficient at the second harmonic frequency of the primary wave can be selectively increased. Introduction of bubbles which are resonant at the second harmonic frequency is proposed as a scheme for practically implementing this idea. In the case of a parametric array, the parameter of nonlinearity also increases when the bubbles are introduced, thus, parametric efficiency can be enhanced while saturation is simultaneously suppressed.

ISSN:0001-4966    

DOI:10.1121/1.2017530

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The prediction of vibration and sound transmission in ship structures is a recent and potentially important area of SEA applications. The developments of these applications in the U.S., Europe, and the Far East is reviewed. These developments include both experimental studies and analytical analyses (including computer studies). There are several issues to be resolved in this work which include the role of in‐plane vibration of the hull and the degree to which reverberation in the structure does or does not dominate traveling wave effects.

ISSN:0001-4966    

DOI:10.1121/1.2017536

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A statistical energy model has been derived for the flexural vibrational power transmission from a shaft to a point‐connected flat plate. Coupling loss factors from shaft to plate are calculated using infinite beam and plate impedances along with lumped‐parameter impedance models of the shaft support. The support is initially treated as a simple mass, transmitting point forces only. Experimental measurements of coupling loss factor for this configuration show very good agreement with the predicted values. The model is then exercized by introducing a spring, first between shaft and mass, then between mass and plate, and finally between two halves of the mass. The implications of the results for vibration isolation problems are discussed. [Research supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2017539

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Intelligibility testing is often the only correct way to evaluate a speech system. Two factors have not been standardized: the talkers' voice quality and the listeners' ability to understand degraded speech. Significant differences exist between test groups because of these factors, so it is not proper to consider the resulting intelligibility scores as absolute values. I propose to coordinate the development of tape recorded word lists to be used as a reference/standard. A group of “representative” talkers, rather than one talker, would read each word list for balanced voice quality. A large representation of the population would evaluate these tapes under various degraded speech conditions to obtain the “reference” scores. Details as to word lists, method of presentation, types of degration, and listener population selection would be addressed by a varied group of interested and qualified investigators.

ISSN:0001-4966    

DOI:10.1121/1.2017547

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

This paper describes a low bit‐rate vocoder designed for improved speech reproduction quality and robustness. The vocoder includes a new algorithm, the Spectral Envelope Estimator, which forms the nucleus of the spectral analyzer. In addition to estimating the speech spectrum, the spectral analyzer also allows determination of a continuous estimate of the background noise spectrum which is used for noise suppression. A maximum‐likelihood pitch estimator, which shares the signal processing of the spectral envelope estimator, has been integrated into the vocoder to yield accurate pitch estimates of noisy speech. This system yields high‐quality speech reproduction at bit rates of 2.4 and 8.8 kbps. [Work sponsored by Defense Advanced Research Projects Agency.]

ISSN:0001-4966    

DOI:10.1121/1.2016895

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Single‐unit and gross potential responses to speech can now be recorded at virtually any level of the auditory nervous system desired. It may be useful at this time to review what is known, what is foreseeable in the immediate future, and what appears to be feasible with the present state of technology. This presentation will focus on conceptual and methodological issues. The time seems appropriate for speech scientists in general, and certainly phoneticians in particular, to participate in the analysis of how the brain processes complex acoustic signals such as speech. [Supported in part by NIH grants.]

ISSN:0001-4966    

DOI:10.1121/1.2016900

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A review is given of the properties of speech sounds that identify different phonetic categories. It is hypothesized that the auditory system gives a distinctive response to sounds with these special properties and hence facilitates classification of the sounds in terms of phonetic categories. The properties that will be discussed include: presence of a rapid spectrum change; presence of an abrupt increase in amplitude; a narrow midfrequency spectral prominence as opposed to a diffuse spread of spectral energy; spectral energy concentrated at high frequencies as opposed to low frequencies; periodic as opposed to nonperiodic sound; spectral characteristics of vowels; presence of low‐frequency sound preceding an onset; two onsets that are simultaneous as opposed to sequential. Evidence for these acoustic properties is presented both from acoustic analysis and from experiments on the perception of speech and speechlike sounds. [Supported by NIH grants.]

ISSN:0001-4966    

DOI:10.1121/1.2016901

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The responses of single auditory‐nerve fibers to simple stimuli (e.g., single tones, clicks) have been studied extensively. The modeling of these response patterns has certainly enlarged our knowledge of how such simple stimuli are processed by the peripheral auditory system. In contrast, such stimuli do not occur often in the natural environment. Current research is turning to the analysis of the responses to complex stimuli, a major example of which are the responses to speech. Nonlinear system theory, in particular, the contributions due to Wiener, yields a systematic method of describing any system—linear or nonlinear. This report will review critically Wiener theory with respect to the special issues of concern in the peripheral auditory system. Attention will focus on whether Wiener theory may yield extra information on models of the peripheral auditory system and whether studies employing this method may be fruitful.

ISSN:0001-4966    

DOI:10.1121/1.2016904

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP