摘要:

Tobacco Mosaic Virus (TMV) particles have been exposed to single pulse acoustic transients of 10−7sec duration produced by the rapid thermal expansion following the absorption of an intense pulse of light from aQ‐switched ruby laser in an optically dense media. A hydrodynamical model is proposed, which relates the observed breakage at the center of the TMV particles, as seen in electron micrographs of exposed particles, to the structure of the TMV particles and to the amplitude and form of the acoustic transient. A velocity gradient of 4 × 107per sec, which produces a force at the center of the TMV particle of the order of the force necessary to break a carbon‐carbon bond, has been found to be sufficient to break the TMV particle.

ISSN:0001-4966    

DOI:10.1121/1.1911355

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

When an intense acoustic stimulus is presented to the rat in a background of steady random noise, the startle reaction is larger than when the same stimulus is presented against a background of silence. Two experiments examined the temporal parameters of this facilitation effect. The initial experiment sought to determine how long the background signal must be present before facilitation can be detected. The second experiment examined the question of how long facilitation persists following termination of a background signal. Results indicated that 100 msec of exposure to a background signal is adequate for full development of the facilitation effect, and that the effect exhibits a significant decline by no more than 8 msec after the termination of a background signal.

ISSN:0001-4966    

DOI:10.1121/1.1911377

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

Three alternate methods for considering the absorbing power of audience seating areas in the calculation of reverberation time in concert halls are treated. The absorption of audience seating, unoccupied and fully occupied, is expressed in terms of (1) equivalent sound‐absorption coefficient αeq, (2) absorption per unit floor area (with edge corrections), αT, and (3) absorption per personaT. Recent data by Meyer, Kuttruff, and Roy, by Kosten, and by Kath and Kuhl are integrated with the author's data to yield new tables of αeq, αT, αS, αR,aT, andaS, where αRis the absorption coefficient of the nonseated areas of a hall, and αSandaSare the absorptions of unoccupied seating on a per‐unit area and per‐seat basis, respectively. The data show that total audience absorption increases in direct proportion to audience area (uniform distribution of persons and well‐upholstered seats assumed), nearly independently of persons in the area. The halls studied have a range of seating densities from 5 to 8 sq ft of floor space per person and have normally diffuse sound fields.

ISSN:0001-4966    

DOI:10.1121/1.1911349

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

This paper describes the new acoustical test facilities of the National Gypsum Company, Tonawanda, New York, comprising one large reverberation chamber, three facilities for measuring the transmission loss of wall structures, one facility for measuring the attenuation over a ceiling‐plenum ceiling path, and one facility for measuring either the transmission loss for airborne sound or the impact isolation of floor‐ceiling structures. The acoustical characteristics of these facilities are compared against the physical requirements stated in existing English‐language measurement test standards.

ISSN:0001-4966    

DOI:10.1121/1.1911357

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

This study is designed to determine whether or not traveling waves accompany harmonic distortion products generated in the cochlea, and also to describe the amplitude distribution of these nonlinear components. Cochlear microphonics were monitored with the differential electrode technique from the first and third turns of guinea pig cochleas. Cancellation of the distortion components was attempted by introducing bone‐conducted pure tones of the frequency of the harmonic and of controllable magnitude and phase. It was demonstrated that harmonic components can never be canceled simultaneously throughout the cochlea. It was shown that the reason for this inability to cancel is that harmonics are not distributed in the cochlea as their own frequency would indicate, but instead they are prominent in the region where their fundamentals are strong.

ISSN:0001-4966    

DOI:10.1121/1.1911371

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

This paper reports the results of tests of the ability of an observer to estimate the distance of speech signals that originate, or appear to originate, at the intersection of the horizontal and median planes in anechoic space. Both live and recorded sources were used over a range of distances from 3 to 30 ft. For such a range (i.e., where differences in the selective effect of air absorption with frequency are relatively small), the results showed a wide difference in observer ability to estimate the distance for these two types of sources. When loudspeaker sources of recorded speech were employed, the judgments reported were essentially independent of the actual distance involved. This was true whether single, multiple symmetrical, or asymmetrical arrays were employed. When a live voice was used as a source, a rather marked degree of ability to estimate relative distance was found depending on the type of vocal output employed and on the degree to which normal level changes with distance were eliminated as a parameter. Use of a shouted voice resulted in overestimating the distance, whereas the apparent distance was foreshortened when a whispered voice was employed.

ISSN:0001-4966    

DOI:10.1121/1.1911372

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

A human observer is less effective at auditory intensity discrimination when the signal is a wide‐band noise than when it is a pure (sinusoidal) tone. An experiment in intensity discrimination of Rayleigh noise shows that amplitude uncertainty seems to govern the discrimination. The empirical psychometric function is found to be only slightly displaced from the performance of an ideal energy detector.

ISSN:0001-4966    

DOI:10.1121/1.1911373

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

This study is designed to determine whether or not traveling waves accompany combination tone components generated in the cochlea, and also to describe the amplitude distribution of these nonlinear products. Cochlear microphonics were monitored with the differential electrode technique from the first and third turns of guinea pig cochleas. Cancellation of the distortion components was attempted by introducing bone‐conducted pure tones at the frequency of the combination tone and of controllable amplitude and phase. It was demonstrated that combination tone components can never be canceled simultaneously throughout the cochlea. It was shown that the reason for this inability to cancel is that combination tones are not distributed as their own frequency would indicate, but instead, they seem to have a distribution peculiar to these nonlinear components.

ISSN:0001-4966    

DOI:10.1121/1.1911374

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The detectability of one binaural tone, masked by another of the same frequency, was measured as a function of the phase difference between them. In one condition, the tone to be detected, the signal, was the same in both ears. In another condition, the signal was inverted at one ear causing a 180° interaural phase difference in the signal. The masking tone was always the same in both ears. It was presented continuously in one experiment, and was gated on and off with the signal in another experiment. In contrast with similar work in which a noise masker was used, binaural signals inverted at one ear are less detectable in some conditions than binaural signals that are the same in both ears: a negative MLD. The negative MLD was largest (about 10 dB) in gated masking conditions and was found to be dependent on signal‐masker duration, growing smaller with longer duration. The detectability of interaurally in‐phase signals as a function of the phase difference between signal and masker can be accounted for by a simple energy‐detection model. However, no existing theory can adequately explain the results obtained with out of‐phase signals, although the results suggest the operation of a system with some of the properties of Durlach's equalization‐cancellation mechanism.

ISSN:0001-4966    

DOI:10.1121/1.1911375

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP

摘要:

The hearing deficiency of a group may be described in terms of the percentage having impaired hearing in order to focus attention on the abnormalities of medical significance. The prevalence of hearing impairment for speech, as defined by the medical profession, was determined for various populations using published hearing survey data. The incidence of hearing impairment was found to increase with age in all populations and also withA‐weighted sound levels in the groups exposed to harmful noise at work. Curves were drawn for estimating the net increase in incidence of hearing impairment resulting from exposure to variousA‐weighted sound levels at work. They show that each decibel of occupational noise above 84 dBAincreases the prevalence of impaired hearing by approximately the same amount as would 1 yr of aging. The curves also indicate that noise exposures that do not exceed the limits currently recommended should cause few additional cases of hearing impairment.

ISSN:0001-4966    

DOI:10.1121/1.1911376

出版商:Acoustical Society of America    

年代:1969

数据来源: AIP