摘要:

The acoustic noise spectrum associated with the collapse of transient cavities produced by a stirring rod in water was measured in the frequency range 1–3500 kc. While the spectrum, in general, goes asf−2above 1 kc, flat regions are found between 20 kc and 100 kc, and again above 500 kc to at least 3500 kc. If the flat regions are due to discrete random impulses, two time constants,τ1≃10−6 secondandτ2<10−8 second, may be obtained by using the criterion 2πfτ≃1, wherefis the −3 db point beyond the flat region.With intense cavitation, the acoustic level fails off and becomes erratic in the 600‐kc region. Transmission measurements made through the cavitating volume show strong sound absorption, which appears to be caused by a cloud of small, stable bubbles.

ISSN:0001-4966    

DOI:10.1121/1.1907341

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The velocity of ultrasonic waves in sulfur hexafluoride (a symmetrical molecule with fifteen vibrational degrees of freedom) has been measured at frequencies of 251.22 kc and 1001.8 kc in the range from 0.38 to 15.89 Mc sec−1atmos−1at 36.10°C. The observed disperison in ultrasonic velocity is ascribed to the slow rate of energy exchange between translational and vibrational states. The dispersion region involves the disappearance of thewholeof molecular vibrational energy, and corresponds to asinglerelaxation time. The relaxation time as derived from dispersion measurements is found to be 5.89×10−7sec at one atmosphere corresponding to 4.68×103a collisions required for energy exchange. The relaxation time for a sulfur hexafluoride mixture with 0.066 mole fraction of helium is found to be 5.46×10−7sec.

ISSN:0001-4966    

DOI:10.1121/1.1907342

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The density and viscosity of the refractive media of the eye have been measured. The velocity of propagation for 5 mc sound waves is found to be 1497 m/sec for the aqueous humor, 1516 for the vitreous humor, and 1616 for the lens. The absorption coefficient was determined at 30 mc for the liquid part of the eye and at 3 mc for the lens.

ISSN:0001-4966    

DOI:10.1121/1.1907343

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The subjective relation “octave of” is demonstrated to be a valid interval for determining scales of musical pitch for pure tones presented successively. Octave judgments of trained musicians have a standard deviation averaging about 0.6 percent. Inter‐observer variability is 2 to 5 times as great, increasing with frequency. Judgments vary significantly from day to day, but as the direction of shift at different frequencies for a single observer is random, the shifts cannot be attributed to changes in the octave criterion. Instead, this variability, and also (1) differences between right‐ and left‐ear judgments of a given observer, (2) the change in difference between subjective and physical octaves as a function of frequency, and (3) the high inter‐observer variability, all confirm the basic instability of pitch‐frequency relations implied by the facts of binaural diplacusis.Individual and group scales of musical pitch are deduced. In these scales, the average rate of change of musical pitch with respect to frequency level is less than unity by a small but significant amount. Although this discrepancy not explained, tests show that it is not an obvious artifact of method. Simultaneous presentation raises variability, but affects means only slightly. The relation betwen the peculiarities of individual scales and binaural diplacusis discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907344

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A two‐component tone was presented under a number of frequency and intensity conditions. The loudness of each component and the total loudness of the combination were traced as the intensity of the higher frequency and were brought from masked threshold to well above masked threshold. Loudnesses were determined by equating the tone or tones under consideration to a comparison tone.When the higher frequency of the pair was at or below 1000 cps, it showed a loudnessloss, relative to its loudness when presented alone, at medium intensities above its masked threshold; but as its intensity was increased, it tended to regain its normal loudness. When the higher frequency of a pair was above 1000 cps, it exhibited agreaterthan normal loudness at medium intensities above its masked threshold which again approached normal with increased intensity. The lower frequency of a pair seemed to be little affected by increases the intensity of the higher frequency within the limits of intensity used. Total loudness tended to be the algebraic sum of the components' loudnesses. The results indicate that the effect of a tone upon the loudness of another is not so simple a phenomenon as a tone's effect upon the threshold of another.

ISSN:0001-4966    

DOI:10.1121/1.1907345

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

There is described an enclosure for a standard loudspeaker mechanism which provides a compact sound source or artificial voice. With a size slightly larger than a human head, the frequency range is 100 to 7000 cps. A simple and reproducible arrangement of damping felt gives unusual flatness.This artificial voice can either be used in free space or with a small chamber arranged as an acoustic labyrinth, for testing microphones and hearing aids. In the chamber, calibrating microphone is mounted opposite the test microphone for continuous monitoring. Simple rc compensating networks are utilized to equalize the sound source for either free‐space or labyrinth measurements.

ISSN:0001-4966    

DOI:10.1121/1.1907346

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Twenty operators were given a task which required answering one of two simultaneous voice messages. The task was performed under a variety of conditions produced by combinations of four experimental “aid” variables: horizontal spatial separation of the sound sources, aural shaping filters which made the tone quality different in each channel, visual cues which indicated the channel about to call the operator, and facilities to “pull down” a desired message from the initial source into a headphone or a loudspeaker near the operator's ear. It was found that the use of horizontal separation and/or the filtered messages greatly improved the operator's performance. Visual cues had no apparent effect on ability to answer the message except when used with pull down facilities. The pull down facilities aided the operator to some extent. Some speculations are advanced about the nature of recognizing and attending to a message in the presence of another message.

ISSN:0001-4966    

DOI:10.1121/1.1907347

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Air control tower operators listened to test transmissions, consisting of speech intelligibility tests couched in airplane‐tower phraseology, over four channels. Part of the time the messages of two channels overlapped each other and the degree of overlap was systematically varied. The task was to respond to all messages.The results showed a decrement in performance related directly to the amount of overlap, the leading message being understood better (unless it was considerably lower in intensity). For those parts of the message which had low informational content, the messages of the overlapping channel increased the total assimilated information per unit time above the total assimilated in the absence of the competing channel messages.

ISSN:0001-4966    

DOI:10.1121/1.1907348

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The effect of several factors upon voice identification was examined. These factors were: the size of the class of possible voices, the duration of the speech signal, the frequency range of the speech signal, voicingvsnonvoicing speech characteristics, and the simultaneous presentation of several voices. One of the most effective factors for speaker identification was the duration of the speech signal. Duration, as such, appears to be important, however, only insofar as it admits a smaller or larger statistical sampling of the speaker's speech repertoire.

ISSN:0001-4966    

DOI:10.1121/1.1907349

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The conventional sound spectrograph affords the analysis of short signal samples and considerable flexibility in the construction of amplitude sections. Other major interests in sound spectrography are in the instantaneous portrayal of signals, and in the permanent record display of continuous linear and logarithmic analyses. This paper suggests instrument methodology for carrying out these operations. Values which are considered practical are suggested for the parameters of certain of the systems which are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907350

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP