摘要:

This paper presents the results of a second experimental investigation of the detection of a signal in noise as a function of signal ensemble size and ensemble frequency range. Data are presented for the three observers who took part in the experiment. The results obtained are compared with (1) predictions based upon three mathematical models, (2) performance expected of a mathematically optimum detector, and (3) results obtained in the first of these investigations.

ISSN:0001-4966    

DOI:10.1121/1.1909461

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

This report presents the results of an investigation dealing with (1) signal discrimination as a function of frequency range of the stimulus ensemble, and (2) the effect of auditory cue on discrimination of auditory stimuli as a function of frequency differences between cues and subsequent stimuli.Data are presented for three observers. The results obtained are compared with predictions based upon the null hypothesis and a narrow‐band scanning model.

ISSN:0001-4966    

DOI:10.1121/1.1909463

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

(1) Loud bursts of pure tone tend to decrease slightly the hydrogen diffusion rate into the first turn of thescala mediaof the eupneic guinea pig and markedly in the hyperventilated animal (2) White noise increases the rate of diffusion of hydrogen gas into the auditory cortex of the nonanesthetized cat. (3) Acoustic trauma produces vascular stasis in exposed blood vessels of the hamster cheek pouch.These results are interpreted as indicating that the endolymphatic hypoxia following loud sound is due to a decrease in the oxygen supply/demand ratio resulting from (a) an increase in metabolism, and (b) no change, or decrease in cochlear blood flow and/or permeability of thestria vascularis.

ISSN:0001-4966    

DOI:10.1121/1.1909465

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

It is shown that when an observer is not farther than one wavelength from an acoustic source, he can determine the distance to the source from measurements of the pressure and of the particle velocity of the medium. The expressions are developed using integrals of the power so that they are relatively insensitive to the pulse shape. Exact expressions are obtainable only in the case of a monopole source. However, a ratioR2is introduced which shows a monotonic dependence on distance in the near field and which is surprisingly insensitive to the nature of the source and to the shape of the wave. Experimental measurements are carried out for a dipole source. Agreement between the theory and the experiment is only moderate because of the difficulty in making sufficiently accurate acoustic measurements.

ISSN:0001-4966    

DOI:10.1121/1.1909467

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A small megaphone was tested for use in direct voice communication high levels of vocal output against backgrounds of noise. Intelligibility scores were determined for 12 talkers, speaking with and without the megaphone, over a range of field voice levels of 70 to 100 db SPL (at 1 m). Nearly the entire over‐all acoustical gain produced by the megaphone was realized in improved intelligibility above backgrounds of white noise and low‐frequency noise. The acoustical gain of the megaphone permitted a lower voice level, and, hence, delayed the deterioration in intelligibility associated with distortions due to shouting. Frequency shifts in the voice spectrum were measured, with and without the megaphone, over a range of vocal efforts from conversational to maximum shout. Control tests demonstrated that the voice‐frequency shifts associated with shouting are not the primary factor in the deterioration of intelligibility; the frequency shifts appear to be only symptomatic of serious vocal distortions in shouting.

ISSN:0001-4966    

DOI:10.1121/1.1909469

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Sound absorption measurements on haired mice, hairless mice, rats, and guinea pigs have been made using reverberation chambers. The initial reverberation‐time experiments on haired and hairless mice were conducted in a cylindrical chamber using a Brüel and Kjaer recorder. Later measurements on all types of animals were made in an asymmetrical chamber using an oscilloscope and an electronic counter. The absorption coefficients were measured in the frequency band from 1 to 20 kc. All experiments showed that the absorption coefficients rise between 6 and 20 kc. Those for the haired animals approach 100%. Hairless mice had lower absorption coefficients approaching 20% at 20 kc.

ISSN:0001-4966    

DOI:10.1121/1.1909471

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The production of a cracking sound by a bull whip is discussed. Photographic evidence shows that the crack is produced by the tip of the whip exceeding the speed of sound and giving off shock waves rather than by the whip slapping itself. This evidence includes motion pictures as well as still shadow pictures which show the tip shedding shock waves. There follows a mathematical discussion of an idealized bull whip with a view to the problem of how the free end of this mechanism achieves a high velocity while the end held in the hand moves relatively slowly. A mathematical solution is given in which it is assumed that a discontinuity in tension propagates down the whip.

ISSN:0001-4966    

DOI:10.1121/1.1909473

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The oscillation behavior of a spherical cavity in an infinite elastic medium is calculated for the case of an incident spherical dilatational wave entirely reflected at the cavity walls. It is shown that there exists for every Poisson's constant 0⩽σ⩽0.5 a frequency for which the amplitude of the oscillating cavity walls becomes a maximum. It is also shown that the amplitude resonance curves are symmetrical and that, assuming loss‐free material, they have a finite half‐width, which is caused by radiation losses and depends only on the ratio of shear wave and dilatational wave velocity.Pulsation oscillations of spherical, rotational‐elliptical, cylindrical, and cubic cavities in rubber blocks were examined experimentally. The pulsation oscillations were excited by means of a sound source coupled to the surface of the rubber block. The sound pressure inside the cavities was measured with a probe microphone. The experimental results for spherical cavities are compared with the theory. Good agreement is found with respect to the resonance frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1909475

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The radiation efficiency of a uniform linear array of point sources with periodic phase variation is evaluated. Two different types of interference are found depending on whether the characteristic length of the phase variation is greater or less than the wavelength of the sound radiated. In its application to suction roll silencing in paper mills it is found to be less effective than a linear continuous phase variation.

ISSN:0001-4966    

DOI:10.1121/1.1909477

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Damage is defined and examples are cited. Illustrative problems of relay contact arm chatter, gyro precession and noise generation, and stress fatigue in a structure are given. It is concluded that there are three means by which damage can be reduced: raising the damage threshold of the item, modifying the transmissibility of the intervening structure, or reducing the severity of the excitation. The examples are an attempt to show specifically how this can be done in practical cases.

ISSN:0001-4966    

DOI:10.1121/1.1909479

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP