摘要:

Measurements of sound propagating from underwater detonations are described, in terms of waveform and spectra. Correlated analytical results are presented, which emphasize the comparative effects of finite amplitude, relaxation, viscosity, and geometrical spreading. A transient (pressure) is defined to be the event between successive crossings of ambient pressure. The reception and analysis of such transients is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1942842

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Delta modulation is a method of single‐bit‐per‐sample analog‐to‐digital conversion utilizing feedback around a hard limiter. The digital patterns produced by a delta modulator can be used for transient detection. The results of investigating the value of delta modulation for transient detection are discussed. Both theoretical results and data from experiments by computer simulation are presented. Limited comparison is made with methods based on measuring energy differences. It is assumed that the only information available concerning the transients are nominal ranges for frequency band, duration, and rise and fall times. The waveforms are unknown.

ISSN:0001-4966    

DOI:10.1121/1.1942847

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The dependence of the noise output of the jet engine upon the eighth power of the exhaust velocity has been firmly established both theoretically and experimentally—at least for the higher subsonic speeds. The advent of the bypass engine and the continued increase of the bypass ratio of these engines have produced a very considerable reduction in the radiated noise. In some instances, however, the reduction has fallen short of that expected, on the basis of an eighth‐power law. It seems probable that other noise sources having a lower velocity exponent now dominate the radiated power. In order to investigate the transition and the nature of these sources, an experimental study using model air jets has been initiated. The effects of both fixed and rotating flow spoilers upon the radiated power have been investigated. Some results of this study are presented in this paper and conclusions drawn regarding the application of these to the real‐life problem of predicting and controlling the noise of the modern jet engine. [Work supported by National Aeronautics and Space Administration, Langley Field, Virginia.]

ISSN:0001-4966    

DOI:10.1121/1.1942850

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Sonic‐boom signatures, including measurements from existing aircraft and predicted waveforms for the supersonic transport, have been reproduced in a laboratory facility. The facility is used to obtain judgments from human subjects on various subjective parameters of sonic booms. This simulation was accomplished using an array of loudspeakers coupled to a 70‐ft3a sealed chamber to produce the appropriate pressure field inside at the subject position. An electronic analog of the sonic‐boom pressure wave, recorded on magnetic tape, is delivered to shaping networks and dc amplifiers, which in turn drive the loudspeakers. Signal‐conditioning in the system includes the response compensation necessary to achieve rise times (associated with the abrupt pressure gradients of the bow and tail waves) of the order of 1–2 msec. The techniques used to generate the electronic analogs of the sonic‐boom pressure waves make it possible to reproduce any waveform for use with the simulator system. Judgment tests comparing the perceived loudness of sonic booms have been carried out for identical signatures, different nearfield waveforms, and signatures differing only in duration.

ISSN:0001-4966    

DOI:10.1121/1.1942859

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Nearfield sonic‐boom theory shows that design modifications can result in reduction of the peak positive overpressure predicted for the critical low supersonic climb régime of an SST. Such modifications, however, may result in performance penalties. In order to perform the indicated tradeoff, values of structural damage potential and human response are needed for the predicted signatures. This paper explores these effects for two candidate SST configurations differing only in area distribution. Generalized structural response envelopes computed by transient time‐history methods indicate little difference in response to the different shaped signatures of the two designs even though the peak positive overpressures differ by a factor of about 1.7. In a simulator of the variable volume type, human subjects judged the signatures to be equally loud at the predicted peak overpressure ratio of 1.7. These results imply that the two designs do not differ significantly in structural‐damage potential or judged loudness and that peak positive overpressure is not a valid criterion for comparing different shaped signatures. Possible explanations of the results are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1942860

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The responses of single auditory‐nerve fibers in anesthetized cats to tonal stimuli were recorded with microelectrodes. Sound‐pressure levels were measured at the eardrum. After correcting for the effects of the middle ear, we were able to compare sensitivities of fibers with different characteristic frequencies. It is difficult to find a single response criterion that will serve as a satisfactory measure of sensitivity for all fibers. Data are presented to show the results of using several sensitivity measures for fibers with different rates of spontaneous activity and characteristic frequencies. The effects of previous stimulation and choice of stimulus parameters on the responses of these fibers are discussed. [Work supported in part by the Joint Services Electronics Program, by the National Science Foundation, by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, and by the National Aeronautics and Space Administration.]

ISSN:0001-4966    

DOI:10.1121/1.1942867

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

By means of an automated single‐lever shock‐avoidance procedure, guinea pigs were conditioned to track absolute thresholds to a thermal noise stimulus. Threshold measurements were made under control conditions and 1–2 h following a single intraperitoneal injection of sodium salicylate. A temporary threshold‐shift function was obtained for dose levels from 50 to 250 ms/ks of salicylate. Contrary to expectation, threshold shifts were not produced when salicylate doses below lethal amounts were cumulated over 4 days' time. Failure to demonstrate drug‐induced TTS under chronic‐dose conditions is discussed in terms of blood salicylate levels. Data are presented that suggest that the analgesic property of salicylate can account in part for the hearing‐loss function obtained with avoidance‐conditioning procedures. [Work supported in part by the National Institute of Neurological Diseases and Blindness, U. S. Department of Health, Education, and Welfare.]

ISSN:0001-4966    

DOI:10.1121/1.1942872

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The prediction of neighborhood reaction to industrial noise can be a complex problem, particularly when the noise sources are intermittent in time and distributed spatially throughout the industrial plant area. In a recent study, such a situation was examined and solved using the method of “composite noise rating,” developed some years ago for application to the aircraft‐ and airport‐noise problems. By this technique, the various parameters relating to the source, the transmission path, and the exposed community are combined to produce contours of equal subjective exposure around the source area. By correlating these contours with different levels of community reaction, we may then differentiate between land areas which will or will not be suited to future development.

ISSN:0001-4966    

DOI:10.1121/1.1942877

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The Jakobson‐Halle description of speech in terms of binary distinctive features is not valid. There are logical inconsistencies if features such as tone and compactness are defined in physical terms. It is impossible to give adequate definitions of features when they are required to be autonomous and relative, and when there are three contrasting linguistic units (such as tones in Yoruba) that differ only in the relative degrees in which they exhibit a particular property (rate of vibration of the vocal cords, or fundamental frequency, or nonlinguistically defined pitch). If the features are not required to be autonomous, the definitions lead to a disguised ternary (orn‐ary) system with a hierarchy of features. If recourse is made to definitions in terms of linguistically determined perceptual classes, then the system is trivial and cannot be said to permit phonetic specifiability of linguistic units is accordance with a universal phonetic alphabet. A better view is that phonological descriptions consist of an ordered set of necessary and sufficient statements linking grammatical statements with physical events. This view requires a new phonological theory.

ISSN:0001-4966    

DOI:10.1121/1.1942887

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Similarity, preference, and loudness judgments were obtained for all possible pairs of 22 voice‐communication circuits, including both linear and nonlinear distortions. Each set of judgments was analyzed, using multidimensional techniques. The analyses indicate that each type of judgment has some factors in common. The interrelationship of these factors and their influence on judgments of circuit quality is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1942893

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP