摘要:

Two captive porpoises (or bottle‐nosed dolphins) were given a variety of tests for their ability to perceive and avoid objects in water by reflected sound signals. The tests were made in a specially constructed anechoic pool in which visual perception was eliminated by the turbidity of the water. The results showed that trains of underwater sound pulses were emitted periodically by the animals in this situation whether they were swimming or at rest. The signals became more numerous when reflecting targets were lowered into the water. Sound pulses could also be triggered by surface splashes, but they were not sustained after a splash if no target was present. These porpoise sonar noises are similar in some ways to man‐made sonar, although they differ from it in several important characteristics.The porpoises would locate and approach food fish by this method but would avoid nonedible objects. They were also able to swim accurately through a field of obstructions without colliding with them—even in darkness. The ability to avoid obstacles by sound did not appear to be affected by artificial jamming noises.

ISSN:0001-4966    

DOI:10.1121/1.1907606

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The identification of the frequency of a tone was examined under four training procedures. The training procedures attempted to determine whether identification of tonal frequency could be improved by attaching distinctive motor responses to elements of the display. For relatively short training periods, such procedures were little more effective than simply providing verbal information of the correctness of the identification.

ISSN:0001-4966    

DOI:10.1121/1.1907617

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Poststimulatory threshold shift has been measured for 1000‐cps stimuli of varying duration and sensation level, turned on and off either without audible transients or abruptly. The measurement was performed by means of test stimuli of varying duration and following the prime stimulus at various time intervals. The results show that the poststimulatory threshold shift depends little on the duration of the test stimulus, but that it depends critically on the time interval between the termination of the prime stimulus and of the test stimulus. The poststimulatory threshold decreases as this time increases. The poststimulatory threshold increases with sensation level and it depends in a complex fashion on the duration of the prime stimulus. The time pattern of the threshold changes radically when a gradual cutoff of the prime stimulus is replaced by an abrupt one. Replacing the 1000‐cps tone by a random noise leads to the same result as an abrupt cutoff.

ISSN:0001-4966    

DOI:10.1121/1.1907619

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The effect of symmetrical speech peak clipping upon speech intelligibility in noise was examined. Over a wide range of conditions, intelligibility is independent of the level of peak clipping if the postclipping speech power is held constant. Peak clipping thus achieves protection of the ear against painfully loud speech without demanding penalty of intelligibility. Indeed, under restricted ranges of conditions, peak clipping may actually improve intelligibility with a constant speech power.

ISSN:0001-4966    

DOI:10.1121/1.1907604

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The scattering, and hence attenuation, of plane dilatational and shear waves due to random orientation of the grains is calculated on the assumptions that (1) the wavelength is large compared to the grain size and (2) the variations in elastic moduli from grain to grain are small compared to the average values of these moduli for the bulk material. Previous treatments of this problem are incomplete; for incident dilatational waves they are valid for a fluid (rigidity modulus=0), and for incident shear waves they describe inadequately the angular dependence of the intensity of the scattered shear waves. It is shown in this paper that for both of these types of incident waves both the scattered dilatational and shear waves are produced; the energy carried away from the incident beam by the latter is32(Vl/Vs)5times that by the former. HereVlandVsare the velocities of the dilatational and shear waves, respectively. The agreement between the theoretical and observed values of the attenuation coefficient is much better than that previously obtained by Mason and McSkimin.The attenuation due to local fluctuations in the density of a medium caused by thermal agitation is also calculated. For solids and liquids this effect is completely negligible. However, for a gas near its critical point, this attenuation is appreciable and rises sharply as the critical point is approached.

ISSN:0001-4966    

DOI:10.1121/1.1907605

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

In order to evaluate the method for measurement of the ultrasonic pressure amplitude in progressive waves which was developed by Loeber and Hiedemann for stationary waves, a comparison between it and two other optical methods was made. Pressure measurements under identical conditions by the three methods are given. Experimental considerations for the use of optical methods for measurement of sound pressure amplitudes are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907607

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Measurements of ultrasonic absorption have been made in dryCO2, and inCO2with hydrogen admixtures, between 19°C and 146°C and at pressures from 0.1 to 650 atmos, and frequencies from 300 kc to 7 Mc. The absorption is described within experimental error by the relaxation formula throughout this range using either (a) a single relaxation time and a single relaxing specific heat representing the total of the vibrational modes, or (b) two relaxation times somewhat more than a factor of two apart, and two relaxing specific heats given by certain combinations of the component vibrations. The relaxation time, or times, varies inversely as the density throughout. The maximum absorption per wavelength comes at 32 kc/atmos at 25°C. Addition of hydrogen shifts theCO2relaxation time by 110 kc/percent by volume ofH2; this amount is in agreement with the shift determined by Knudsen and Fricke, provided their data is interpreted as being by volume and not by weight. The “classical absorption” at low pressures is 1.5 times the theoretical value.

ISSN:0001-4966    

DOI:10.1121/1.1907608

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Acoustic propagation in plate‐shaped solid delay lines is analyzed using diffraction theory. The analysis yields the dependence of group velocity (time delay), phase velocity, pulse shape, pulse rise time, output amplitude ripple spacing, and ripple amplitude on the parameters of frequency, delay line length, free‐medium sound velocity, and plate thickness. Data are presented corroborating the theory quantitatively for time delay dependence on frequency and plate thickness, ripple spacing dependence on frequency and mode, and pulse rise‐time dependence on frequency. The diffraction theory is compared to the wave equation plane‐wave solutions for infinite plates. The results of the diffraction analysis are more appropriate for the description of sound propagation in plate‐shaped delay lines.

ISSN:0001-4966    

DOI:10.1121/1.1907609

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The study of the asymmetry of the light diffracted by ultrasonic waves progressing with moderate amplitudes in liquids is used to detect and measure the finite amplitude distortion in water and carbon tetrachloride. A theory is developed which relates the distortion present to available isothermal compressibility measurements. This development includes the presence of absorption.Measurements of the second harmonic were made in water at 2 Mc and 4 Mc, at distances up to 50 cm, and at peak ultrasonic pressures between zero and 1.5 atmos. More detailed measurements were made in carbon tetrachloride at frequencies of 2 and 3 Mc, at distances up to 21 cm, and at pressures up to 0.7 atmos. For both liquids, good agreement is obtained between the experimentally measured values and the theoretically predicted results.Small amounts of distortion were easily measured. The second harmonic could be measured when the intensity of the harmonic was less than 0.04% of the intensity of the fundamental. Distortion could be measured when the fundamental was much less than 0.2 atmos.

ISSN:0001-4966    

DOI:10.1121/1.1907610

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

In the research reported here an attempt has been made to discover by experiment what physical assumptions and approximations are appropriate in the theory of cavitation microstreaming, especially for cavitation bubbles located near solid boundaries. A systematic investigation of the phenomenon has been made and its dependence on certain parameters (e.g., amplitude of sound) has been determined. The investigation has disclosed that as the sound amplitude is varied, other conditions remaining the same, the streaming changes discontinuously through several stable regimes. It appears that in order to account for the generation of vorticity one needs to assume different conditions at the boundaries for each regime. For at least one regime, a theoretical model due to Nyborg seems to be applicable; comparison made with experimentally determined streaming velocities.

ISSN:0001-4966    

DOI:10.1121/1.1907611

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP