摘要:

To further test the hypothesis that periodicity pitch is mediated, at least peripherally. by neural fibers which ordinarily respond to high frequencies, the phenomenon of residual masking or short‐duration auditory fatigue was employed. Pure tones of 150 and 2200 cps, and a 2200‐cps signal pulsed 150 times per second all at several levels, were used in all combinations as fatigue and test stimuli. The results support the findings of Small and Campbell with respect to the masking of periodicity pitch. Perhaps the most interesting observation was that, if a pulse signal at moderate levels was used as the fatiguer, thresholds were shifted significantly for the 2000‐cps and pulsed signals, but were not shifted for the 150‐cps signal, even though pitch of the fatiguer corresponded to this frequency. Only when the level of the fatiguer was raised to 100 dB SPL, a level which almost certainly will give rise to nonlinear effects—i.e.—enveloped detection. did significant threshold shifts appear at the frequency of the pulse rate, 150 cps.

ISSN:0001-4966    

DOI:10.1121/1.1937043

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Two word‐intelligibility experiments were conducted under free‐field conditions to determine how intelligibility depends upon the distance and angle between the talker and a group of listeners. The talker stood at the apex of a quarter pie‐shaped section of listeners. In the course of experiment 1, the talker faced the center radial of listeners (0°), then rotated away from the center in 15° steps to 90°, and finally faced 135° and 180° . The listeners in both experiments either faced the talker's position (0°) or faced away from the talker's position through angles of 15°, 30°, 45°, 60°, 75°, or 90°. The results showed that speech intelligibility was quite uniform over a 90° horizontal arc centered on the speech axis, and that intelligibility was increased slightly when the listening angle was between 15° and 75° in azimuth as compared to 0°.

ISSN:0001-4966    

DOI:10.1121/1.1937048

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Missile rocket‐engine noise‐ and vibration‐measurement system components are subjected to severe environments which may introduce spurious signals in the data. Thus, all components and systems must be subjected to environmental tests prior to their use to assure good data quality. Such a program is described in this paper. Several types of commercial microphones. accelerometers, preamplifiers, and cables were subjected to environmental tests, and their outputs analyzed to determine effect upon data. In addition, an entire data‐acquisition system (to recorder input), including mounting brackets, was subjected to vibration tests. The results are discussed in the following manner: (a) Test data are graphically presented. (b) Test results are analyzed to predict their effect on the data. (c) The results of the prediction are compared to measured missile data. (d) Individual components and system test data are compared to show differences in results. Both good and poor data taken from missile firings are also presented to show environmental effects.

ISSN:0001-4966    

DOI:10.1121/1.1937054

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The problem, originally proposed by Rayleigh, of the reflection of a plane acoustic wave from a pressure‐release surface is given an exact formulation suitable for numerical computation. Calculations, carried out on the Argonne IBM 704 and the UCSD CDC 1601 are described and results presented. [This presentation represents results of research sponsored by the Office of Naval Research and the U. S. Atomic Energy Commission.]

ISSN:0001-4966    

DOI:10.1121/1.1937060

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An extended study of diffraction of acoustic waves in the audible range is currently under progress in the anechoic chamber at Temple University. A probe microphone has been constructed by coupling to a12‐in.Bruel and Kjaer (B&K) capacitor microphone a rigid steel tube with a precision‐drilled 1‐mm‐diam hole. The output is fed into a B&K audio‐frequency spectrum analyzer and recorder. Since the measuring apparatus is so important in experimental studies in diffraction, extensive tests have been run to check the free‐field characteristics of the chamber and the frequency and directional response of the probe microphone. As a test of the precision of the apparatus, the diffraction patterns for rigid cylinders and spheres have been analyzed for various values ofka(ratio of circumference to wavelength) from 0.2 to 10. To obtain continuous readings, the microphone has been mounted to rotate at 2 rpm. The results have followed theory predictions in every respect, and the details of the “bright spot” and the numerous lobes at higher frequencies are clearly revealed by the continuous recordings. Studies on cylinders and spheres in 2‐ and 3‐dimensional arrays have been investigated. It is hoped that generalizations drawn from these results will lead to suggestions for mathematical approaches to solutions. [This work was supported by a Research Grant from Temple University.]

ISSN:0001-4966    

DOI:10.1121/1.1937066

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Underwater objects always acquire a growth of marine organisms when left in the water for a period of time. When a natural growth of fouling occurs on a hydrophone, a reduction of its sensitivity and a deterioration of its beam pattern may be expected. In order to estimate the severity of these effects, a small selection of hydrophones was measured after they had remained in Chesapeake Bay during the growing season of 1961. Measurements of beam pattern and receiving response were made in the fouled condition and after the fouling had been cleaned off. Reductions of axial sensitivity ranging from zero to 10 dB were found in the frequency interval 1 to 20 kc. Appreciable, though not severe, effects of the fouling on the hydrophone beam patterns were observed. Additional work is needed for making prediction estimates for surveillance systems or other uses.

ISSN:0001-4966    

DOI:10.1121/1.1937070

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The development of mixing engines (such as bypass and turbofan engines) has opened a new area to be explored for possible means of reducing jet noise. Analytical studies and experimental developments were made so that the noise characteristics of various mixing engines could be identified in terms of engine‐design parameters. The method of the program was based on an analysis of engine‐flow parameters, such as fan‐pressure ratio and bypass ratio, in terms of energy distribution in the primary and secondary jet streams. The results revealed that (1) in geometrically different exhaust‐nozzle configurations (ranging from short duct through coplanar to fully mixed), jet noise decreases as the mixing of 2 flows becomes more complete; and (2) appropriate combinations of engine variables (such as high bypass ratio with high fan‐input energy) will lead to a significant reduction in the jet noise from bypass engines. The results of this program will provide the menus of establishing acoustically optimum design criteria for bypass engines.

ISSN:0001-4966    

DOI:10.1121/1.1937080

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

A whine in the noise background of a coasting automobile presented a quality‐control problem to the manufacturer. The objectionable signal had the character of a sinusoidal sound whose frequency was velocity‐dependent and which faded in and out of the background noise as speed decreased from 70 to 20 mph. This whine was attributed to the differential gears. The analysis undertaken to determine the nature of the whine, its association with the differential gears, and the explanation for the details characterizing its occurrence are described. In addition, the design of an instrument to be used in the inspection line for detection of incipient noisy cars is presented. [Supported by American Motors Corporation, Kenosha, Wisconsin.]

ISSN:0001-4966    

DOI:10.1121/1.1937083

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The possibility of having a sensation of pitch associated only with a bilateral presentation of acoustic stimuli to the listener was first discovered by Huggins [Cramer and Huggins, J. Acoust. Soc. Am.30, 413–417 (1958)]. Huggins employed a single, smooth‐frequency‐spectrum noise generator, and fed its output directly to one ear, but via an all‐pass phase‐changing network to the other. In the present work, the possibility that this effect is a by‐product of a process of auditory localization has been considered. This has led to the experimental use of a family of new binaural pitch‐producing stimuli obtained from a multiplicity of independent, smooth‐spectrum noise generators which operate in conjunction with continuously variable all‐pass delay lines. Each stimulus configuration may be associated with a simple localization pattern. The pitch associated with a particular pattern depends both on its form and on the magnitudes of the delays involved. Pitch‐matching measurements with these stimuli and a comparison with the more complex pattern of localization which might be associated with the Huggins stimuli support the view that these binaural pitch phenomena are mediated by a process akin to localization rather than by a central frequency‐analysis mechanism.

ISSN:0001-4966    

DOI:10.1121/1.1937091

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Speech distortion is defined as any operation that evokes inappropriate behavior by a listener in response to speech. Two categories of distorting operations are distinguished: (1) response‐independent, in which the transfer function applied to the original speech signal is not determined by the probable response of the listener (e.g., masking, filtering); and (2) response‐dependent, in which the distorting operation is related to the probable response of the listener during undistorted transmission and, therefore, may be specified in linguistic terms (e.g., foreign accent). Two experiments compare the effects of these 2 types of distortion. Twenty‐four midwestern Americans listened to recorded articulation lists rendered by 1 American and 3 foreign‐born speakers under 8 conditions of masking and filtering. Reducing the speech‐to‐noise ratio to 20 dB or the transmission bandwidth to 500 cps yields approximately 50% reduction in word articulation for both native‐ and foreign‐accent speech. The latter was approximately 40% less intelligible than native speech under all experimental conditions. A “phonetic difference” measure of the degree of foreign accent holds promise as a predictor of the effects of accent on intelligibility; a significant correlation ratio of −0.66 was obtained.

ISSN:0001-4966    

DOI:10.1121/1.1937093

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP