摘要:

A system for delivering a sinusoidal signal of known sound pressure to the ear at high frequencies (8–20 kHz) is explored. A high‐frequency driver unit is coupled to the ear canal through a long tube, so that the acoustic source at the ear‐canal entrance had an impedance close to ρc. The system is calibrated by applying an impulse of voltage to the source and measuring the response at a small microphone located in the coupling tube close to the ear‐canal entrance. A signal‐processing procedure detects the zeros in the spectrum of this response and uses these data to estimate the transfer function from the source voltage to the sound pressure at the inner end of the ear canal. The system has been calibrated for a number of different ears in this way, and data giving the range of characteristics of the ear canals as determined by the zero locations will be described. In general, the results are consistent with theoretical predictions based on the known average shape of the ear canal. [Supported by a contract from NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2021277

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

“Rollover,” poorer word identification accuracy at high than at low SPLs, is correlated with the absence of the acoustic reflex in individuals with lesions to c.n. VII and c.n. VIII. The increased number of word identification errors at high SPL is due largely to errors in vowel identification. Individuals with these types of lesions, however, are rare. In order to study rollover in a normal population, we constructed 10 vowels of 50‐ms duration. These were presented to normal hearing listeners at moderate and high SPLs. We reasoned that, since the latency to onset of the acoustic reflex, at the test levels, was longer than the total duration of the vowels, we should observe poorer vowel identification at the higher SPL than at the lower. This was, in fact, the outcome. Vowel confusions were usually with vowels with higherF2 and lowerF1. This outcome was confirmed by the results of identification tests with stimuli along an /i/‐/ε/ continuum.

ISSN:0001-4966    

DOI:10.1121/1.2021281

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The main temporal characteristics of discharges observed in the primary auditory neuron are the phenomena of adaptation and synchronization of the responses on the phase of the stimulus. These phenomena play a major role in the mechanisms of speech coding [Delgutte, J. Acoust. Soc. Am.68, 843 (1980)]. We propose a stochastic threshold model which mainly asumes that the process of adaptation is additive. This model reproduces appropriately adaptation and its per‐stimulatory effects. It simulates in the same way the locking of nerve discharge to the stimulus cycle up to about 5000 cycles/s, in accordance with experimental results (Andersonet al., J. Acoust. Soc. Am.54(2) (1971)]. In comparison with other threshold models, the originality of ours lies in the fact that it includes the temporal evolution of graded potentials described by Furukawaet al.[J. Physiol.276(1978)].

ISSN:0001-4966    

DOI:10.1121/1.2021283

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Two‐tone interactions are recorded in the responses of single units in the superior temporal gyrus to contralateral acoustic stimulation of the awake squirrel monkey. Four response types are distinguished based primarily on the nature of the two‐tone response, and secondarily on criteria such as the patterns of response to single tones and noise stimuli, thresholds, and spontaneous activity levels. Type A units (24/80) display strong lateral inhibitory influences which may extend up to two octaves on either side, or both sides, of the BF. They are sharply tuned at all intensities, and generally exhibit sustained response to single‐tone stimuli at the BF. The units have nonmonotonic rate‐level functions, and where tested, show little or no response to broadband noise. Most type A units have low spontaneous rates (20 spikes/s) and inhibitory responses to single‐tone stimuli. Broadband noise is applied to a few type B units, and in all cases it evokes strong excitatory response. Type C units (17/80) summate the responses to the two‐tone stimulus, and show little or no inhibitory influences. They have V‐shaped tuning curves, monotonic rate‐level functions, low thresholds (<30 dB SPL), moderate spontaneous rates (∼ 10 spikes/s), and a strong and sustained response to noise and single tone stimuli. Type D units (17/80) show “temporal inhibition” to two‐tone stimuli, in that an excitatory response to the first tone suppresses (adapts or inhibits) the response to the second tone. These units generally have moderate to broad frequency tuning and phasic responses to single tone stimuli. Histological examination of electrode tracks suggests that type A units are restricted to A1 (and possibly the rostral field) while other types are distributed over all auditory fields.

ISSN:0001-4966    

DOI:10.1121/1.2021288

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

One of our major interests in the past few years has been in the development of diphasic transducer materials made from polymers and lead zirconate titanate (PZT) ceramics with high hydrostatic pressure sensitivity. The concept of phase connectivity, the manner in which the individual phases are interconnected, has been used to optimize the electric flux pattern and mechanical stress distributions in attaining remarkable improvements in the hydrostatic strain coefficient (dh) and the hydrostatic voltage coefficient (gh) over the corresponding values of solid PZT ceramics. Recent results on 0‐3, 1‐3, 1‐3‐2, 2‐2, 3‐1, 3‐2, and 3‐3 composites will be presented, and a comparison made with polyvinylidene fluoride and other hydrophone materials. When driven at high frequency the composite transducers exhibit a number of interesting modes of motions in which the component materials sometimes vibrate out of phase. Some of the proposed applications for composite transducers will be described.

ISSN:0001-4966    

DOI:10.1121/1.2021292

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

We quantitatively analyze the effect of hydrostatic pressures on the static and dynamic effective material properties of perforated visoelastic elastomers. A resonance methodology that we had developed earlier [i.e., G. Gaunaurd and J. Barlow, J. Acoust. Soc. Am.75, 23–34 (1984)] is here extended to account for the distorting effect of added pressures. The distortion basically produces a broadening of the spectral plots and a shift in the resonance peaks/dips that are observed in the dynamic plots of all the effective properties of the pertinent composites. For the lossy, air‐filled rubberlike materials considered here the pressure effect is quite noticeable but smaller than the viscous effect or than the effect of nonuniformity in the cavity size‐distribution functions that we analyzed earlier. The model is implemented by a computer code and its numerical predictions are quantitatively displayed for some of the most important of the effective material properties of a given perforated elastomer up to applied pressures of 400 psi. These perforated elastomers have uses as underwater sound absorbers. [Work partially supported by NOSC, San Diego, CA and by NSWC, White Oak, MD.]

ISSN:0001-4966    

DOI:10.1121/1.2021295

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

In systems used to simulate wind instrument behavior the blowing pressure is often set to some constant value. This is equivalent to assuming that the blowing pressure source (lungs‐bronchi‐trachea‐vocal tract) has an internal impedance that is small in comparison with reed‐aperture plus tube impedance. A stylized pressure source plus reed‐aperture plus tube is simulated to investigate the effects of source characteristics and tube characteristics. The pressure source is represented by one of four configurations: large cross‐sectional area vocal tract, small cross‐sectional area vocal tract, an /a/‐shaped tract, and an /i/‐shaped tract. The rectangular “reed‐aperture” is parametrized so that its time variation is independent of any source or tube loading. Four “tube” loadings are simulated: a zero impedance, a resistance, an inertance, and a section of uniform tubing. Waveforms and spectra are calculated for air flow through the reed‐aperture, blowing pressure, and tube pressure for the 4 × 4 = 16 possible combinations to demonstrate the effects of source and tube characteristics.

ISSN:0001-4966    

DOI:10.1121/1.2021303

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The current Occupational Safety and Health Review Commission precedent on the feasibility of engineering noise controls isSun Ship, Inc., a 1982 decision. In that case Commissioners Cleary and Cottine reached a consensus on the meaning of the term “feasible,” on which they had not been able to agree earlier inSamson Paper Bag. BecauseSamson Paper Baghad not achieved a consensus on a new definition, the Commission there concluded that its original cost‐benefit test (Continental Can) would remain in effect. Commissioners Cleary and Cottine now agreed to reject that test on the basis of the Supreme Court's 1981 decision in the “cotton dust case,”American Textile Manufacturers Institute, Inc., vs. Donovan(ATMI). The Court's decision, however, interprets and is predicted on a different provision of the Occupational safety and Health act than that under which the noise standard was promulgated. In a subsequent appellate decision,Castle&Cook Foods, the Ninth Circuit specifically concluded that the ATMI decision does not control the interpretation of the noise standard and that the Commission's previous cost‐benefit test was reasonable.

ISSN:0001-4966    

DOI:10.1121/1.2021309

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The role that economic feasibility plays in employer compliance with (and OSHA enforcement of) health standards in general and the Noise standard in particular. Industries' problems with compliance with the Noise Standard and Hearing Conservation Amendment, particularly small business' problems. Preference for effective hearing conservation programs over government insistence of engineering controls. A comparison of the Reagan and Carter Administrations' Hearing Conservation Amendments. Industry objections to the current rule: (1) integration to 80 dBA; (2) inclusion of impulsive noise; (3) requirement ofannualaudiometric testing in all cases (instead of biennial or periodic); (4) qualification of the area sampling provision; and (5) general length and complexity (as unnecessary impediments to small business compliance). Support for OSHA compliance directive interpretingCastle&Cooke Foods, CPL 2‐2.35. The cost‐benefit issue in general, and the impact of the Supreme Court's 1981 cotton dust decision and Executive Order 12291 on cost‐benefit analysis. Industry's position regarding further rule‐making on the Noise Standard.

ISSN:0001-4966    

DOI:10.1121/1.2021310

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The implementation of engineering noise controls on existing, rebuilt, and new equipment must take into account both technological and economic feasibility. Retro‐fitting engineering controls to existing noisy equipment on the production floor, while desirable and in some instance necessary, can have serious negative economic consequences. Costs resulting from decreased productivity, increased maintenance, frequency of replacement, and possible increased floorspace requirements are all factors which must be considered. General Motors Corporation, (GM, while pursuing the investigation and implementation of feasible engineering noise controls on existing equipment, places special emphases on the purchase of new equipment. The “General Motors Corporation Sound Level Specification for Machinery and Equipment,” Revision February 1979, specifies a maximum time‐weighted average sound level of 80 dB (A). Measurements are taken at the operator's ear location and on the measurement envelope as specified in “NMTBA Noise Measurement Techniques” Second Edition dated January 1976. GM, working in conjunction with its suppliers, has experienced considerable success in achieving feasible engineering controls through the application of the GM Purchase Specification.

ISSN:0001-4966    

DOI:10.1121/1.2021316

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP