摘要:

Both the overall aging of the population and its exposure to higher noise levels have increased the tendency to hearing loss and the importance of improved hearing aids for speech perception. This article reviews improvements in conventional electroacoustic hearing aids, as well as recently developed alternative classes of speech‐perception aids, including surgically implanted cochlear stimulators, and vibrotactile, electrocutaneous and optical stimulating devices. It is concluded that the most effective aid for the vast majority of hearing‐impaired persons is, and will remain for the immediate future, the electroacoustic hearing aid. In those cases for which no benefit is demonstrated for the electroacoustic aid, generally meaning persons with profound hearing loss, either the cochlear implant or a tactile aid may provide some improvement in the understanding of speech. In rare cases, some speech understanding in the absence of lip reading is achieved by patients with cochlear implants, for unexplained reasons. This and other pressing questions about speech processing need to be addressed by the research community if more effective aids are to be developed for the use of the 36.5 million hearing‐impaired persons expected in the U.S. by the year 2050.

ISSN:0001-4966    

DOI:10.1121/1.402341

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A piezoelectric vibration can be characterized by the components of its electric equivalent. The dynamic nature of these components, as well as their dependence on the location of the electrodes on a piezoelectric structure, is studied in this article. General equations, based on a decomposition of a known vibration into its eigenmodes, are derived for a flexural vibration. A correction factor for the dynamic and geometric properties of the equivalent components is derived. The mechanical compliance of the beam is shown to depend on the choice of electrode configuration. The behavior far from resonance is also studied. It has been assumed that the mechanical and the piezoelectric properties can be treated as two quasiseparate problems.

ISSN:0001-4966    

DOI:10.1121/1.402347

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Two adjacent mechanical systems usually affect each other. This is particularly noticeable if their resonance frequencies are almost equal. A simple way of describing this phenomenon, for second‐order mechanical systems, is derived in this article. It is shown that the mechanical coupling can be described with the help of an ordinary electric equivalent circuit. The components in the equivalent circuit are easily measured electrically, for instance, with the help of piezoelectric and magnetostrictive devices, strain gauges or with an impedance meter. It is also shown how useful information can be extracted from measurements in a simple way. Predictions of the vibration amplitude of a second system, caused by a first system, can easily be made, if the values of the equivalent components are known. The behavior of the systems in the absence of the coupling can also be predicted from the (electric) measurements.

ISSN:0001-4966    

DOI:10.1121/1.401939

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Layered piezoelectric resonators exhibit a complex spectrum of eigenfrequencies, which can be understood better if the associated vibration patterns are examined. For a closer insight into such a system, planoconvex AT‐cut quartz crystals with a thick layer of copper on one side are investigated experimentally. Since presently no comprehensive three‐dimensional theory of layered resonators is available, the experimental results can be compared only with one‐dimensional descriptions of layered resonators or with theoretical models for unloaded contoured quartz crystals. The anharmonic spectrum of the crystals is used to find a formula by which the eigenfrequency of the corresponding infinite plate can be determined from measured frequencies of planoconvex crystals. If this correction is applied to experimental frequency spectra of composite quartz‐film resonators, excellent agreement with the one‐dimensional model is found. As theoretically predicted, also even harmonic overtones of heavily loaded crystals can be excited electrically. The vibration patterns are examined with an ultrasensitive laser‐speckle technique. The measurements of the odd harmonic overtones agree well with the theory of energy trapping in planoconvex quartz crystals. An increase of the crystal’s active area with increasing mass load is observed. The even overtones frequently exhibit no such energy trapping; in these cases, unusual vibration patterns occur.

ISSN:0001-4966    

DOI:10.1121/1.401940

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The psychophysical relations between loudspeakers’ frequency response and their perceptual properties were investigated. The frequency response of 18 high‐fidelity loudspeakers was measured in three different conditions: in free field, in reverberation room, and in the listening room itself. The perceptual data consisted of experienced listeners’ ratings of the same loudspeakers in seven scales: clarity, fullness, spaciousness, brightness, softness, absence of extraneous sounds, and fidelity (Gabrielsson and Lindström, 1985). Hypotheses concerning the psychophysical relations were stated on the basis of results from earlier listening tests. The relations obtained with measurements in the listening room showed better agreement with the hypotheses than those obtained by measurements in free field or in reverberation room.

ISSN:0001-4966    

DOI:10.1121/1.401941

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Near‐field acoustic intensity measurements are a powerful analysis and diagnostic tool when all available measured quantities are utilized. The advantage of considering the reactive intensity and complex specific acoustic impedance along with the active intensity is stressed. An added feature to the data presentation is the pressure phase that is reconstructed from the time‐independent measured data. The active intensity plots are thus enhanced by superimposing the lines of constant phase so that the wave‐front propagation is visualized. In the first measurement configuration, an active source absorbing power is differentiated from a resonant cavity absorbing power and diffraction is localized. In the second configuration, the mode shape of a vibrating plate is identified.

ISSN:0001-4966    

DOI:10.1121/1.401942

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

An acoustic near plane‐wave absorption spectrometer has been developed for use in small samples of liquid (30 ml) over bandwidths of up to 60 MHz, using a two transducer short‐pulse transmission technique. The instrument is controlled by computer, and on‐line digital signal processing is used to correct for transducer insertion, radiation coupling, and the transient responses of transmitter and receiver electronics. The raw data acquisition time is short and the instrument in its present form could be used to estimate absorption at 100‐ms intervals. The instrument can be used on both stationary chemical systems and systems undergoing chemical reaction. Experimental results are presented that show excellent agreement with absorption measurements by traditional (slower) techniques.

ISSN:0001-4966    

DOI:10.1121/1.401943

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Sonar and radar measurements both indicate that there are fundamental problems with the present wind–wave models of the sea surface at higher wave numbers: Backscattering strengths at high frequencies and small grazing angles are much greater than predicted 0(10–20 dB). In addition, the Doppler spectra show no evidence of the dispersion expected in gravity‐capillary régimes. The usual quasilinear wave theories do not account for such effects. Accordingly, a new qualitative four‐stage model for wave growth is proposed: (1) initiation of high‐frequency surface ripples (catspaws) by the wind; (2) nonlinear formation of steep wave fronts; (3) generation of low‐frequency waves by surface instability and wave–wind interaction; and (4) continued generation of unstable surface‐disturbances which chaotically degenerate into ensembles of solitons, undergoing continuous creation and absorption, with the incoming energy balanced by dissipation. A preliminary theory of the resulting soliton‐surface layer is discussed by D. Middleton [ComputationalAcoustics(North Holland, New York, 1988)]. Here, a broad range of experimental evidence is presented, in support of the proposed surface mechanism developed by Middleton. Thus, with assumptions not contrary to any of the known properties of the sea surface, quantitative scattering predictions of the model are seen to agree well with experiment, in particular with respect to backscattering strength, Doppler shift, and (point intensity) spectral levels, produced in known ‘‘bubble‐free’’ régimes. These results provide extensive inferential support for the sea‐surface and scattering models proposed here. However, further research is needed for explicit verification by direct observation and testing against more refined measurements of wave statistics and hydrodynamic theory.

ISSN:0001-4966    

DOI:10.1121/1.401944

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

McIntyreetal. [J. Acoust. Soc. Am.74, 1325–1345 (1983)], through comprehensive time‐domain analyses of the bowed string mechanisms and various numerical simulations, have first pointed out that the hysteretical character of the sticking–slipping process necessarily induces, under certain end conditions, a flattening effect (the note plays flat as the bow pressure exceeds a given level). Taking advantage of a frequency‐domain analysis, it is demonstrated that the area of the hysteresis cycle has an analytical relation to various physical parameters of the bowed string, leading to the concept of reactive power. The flattening effect appears as a consequence of this relation. Another possible consequence is the observed dependence of the spectrum and intensity of the string vibration on the bow pressing force. Based on realistic assumptions, an algorithm is proposed to connect the flattening effect or the intensity variations to the physical characteristics of the string. Finally, the variations of the flattening effect with playing parameters such as bow position or bow velocity are evaluated.

ISSN:0001-4966    

DOI:10.1121/1.401945

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Hearing aid benefit depends primarily on the extent to which amplification facilitates speech understanding in typical everyday listening environments. In the hearing aid fitting process, improved speech understanding is often measured in an audiometric test room. However, because audiometric test rooms are smaller, quieter, and less reverberant than typical rooms, these data may not accurately predict speech understanding in daily life. This study was undertaken to evaluate the validity of three simulated real‐world listening environments created in an audiometric test room. The three environments represented a typical living room, cocktail party, and classroom, respectively. Twenty normal‐hearing subjects, listening monaurally, provided intelligibility scores for four phonetic contrasts produced by each of three normal talkers. Intelligibility obtained in the real environment was compared with that measured in the corresponding simulated environment. Results indicated that the relative intelligibility of talkers and phonetic contrasts remained essentially constant across each real‐simulated environment pair, and that significant talker × contrast interactions seen in the real environments were usually reproduced in the simulated environments. However, there were somewhat fewer significant intelligibility differences in the simulated environments than in the real environments. Also, the intelligibility of one talker deteriorated more than expected in the simulated reverberant environment. Overall, the outcome suggested that these typical listening environments were rather accurately simulated (for monaural listening) in an audiometric test room using appropriate adjustments of presentation level, signal‐to‐babble ratio, and synthetic reverberation effects.

ISSN:0001-4966    

DOI:10.1121/1.401946

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP