ISSN:0001-4966    

DOI:10.1121/1.1918188

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Most ray‐tracing schemes involve many numerical computations. At least one of these calculations can be simplified. The calculation for ray travel time through a layer of constant velocity gradient has been performed by calculating the first few terms of an infinite series. This method, in addition to being laborious, can lead to approximations. An alternate method employing log tables is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1918190

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

From anatomical, physiological, and psychophysiological investigations, it appears (a) that nerve impulses aroused by sound striking the two ears interact in a lower brain‐stem center of the auditory system, probably in one part of the superior olivary complex; (b) that the neural information which is necessary for localization of sound in space remains in the form, “time differences between nerve impulses.” as it is transmitted to higher centers of the brain; and (c) that the auditory areas of the cerebral cortex are essential for the full utilization of this neural information which makes possible the accurate localization of sound in space.

ISSN:0001-4966    

DOI:10.1121/1.1937148

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

In the frequency range from 60 kc to 1 Mc, the boundary conditions at the free surfaces are very complex. A diliational wave reflected from a boundary such as the ends of a rod may be decomposed into a shear wave, which is generated upon reflection of the diliatational wave, and a diliatational wave. The amplitude of the reflected diliational wave is decreased due to the energy conversion upon reflection as well as the attenuation of the material. The measured loss factor is, therefore, not indicative of the energy absorption of the material. In order to obtain an accurate measurement of the absorption, specimens in the shape of cones, hemispheres, and spheres were investigated. Corrections were also made for effects of dispersion. Identification of the modulus associated with the sound velocity in a frequency range above and below the dispersion region was attempted. (This work was supported in part by the U. S. Atomic Energy Commission.)

ISSN:0001-4966    

DOI:10.1121/1.1937154

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Recordings of bottom‐pressure fluctuations were made in San Diego Bay in April 1960 and in January 1961 to study the seiche phenomenon. A solion infrasonic hydrophone was utilized as a bottom‐pressure transducer to detect pressure fluctuations over the range of 5‐ to 1600 sec periods. Analysis of the bottom‐pressure records consists of computing relative power spectra estimates and autocorrelation functions after the raw pressure data are handpass filtered. From the relative power spectra and limited theoretical considerations, it was determined that there is an active longitudinal seiche with a second harmonic period of 1450 sec. A description of the solion infrasonic hydrophone is presented along with the recording and analysis system.

ISSN:0001-4966    

DOI:10.1121/1.1937159

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

High‐tensile steel tubing, when preformed to an elliptical cross section, can provide pressure release for high‐power, low‐frequency, underwater‐sound projectors up to depths where the hydrostatic pressure stresses the tubes beyond the yield‐strength limit. The compressibility of the compliant tube is essentially constant up to the point where the material yields. When using compliant tubes for pressure release, the volume of tubes is chosen such that their volume displacement (compressibility) is equal to the volume of fluid displaced by the active transducer elements. The dimensions of the tubes are such that they are operated well below resonance; hence, a 1:1 compliance ratio exists between the driver element and pressure‐release system. When the dimensions of tubes and of tube cavities are such that operation is near the resonance condition, the apparent compliance of the system increases, and a lesser number of tubes can be used to provide pressure release. Pressure‐release systems, using compliant tubes made from heat‐treated 4130 steel, have been built for use at depths to 2000 ft. Comparison tests between a transducer using a pressure‐regulated air‐release system and the compliant tube‐release system have been made, and the performance of the transducer is essentially unchanged.

ISSN:0001-4966    

DOI:10.1121/1.1937163

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Several years ago the Lincoln Laboratory developed a special‐purpose computer [MAUDE] to decode hand‐sent Morse signals. Since the computer was to handle all kinds of Morse, including cipher, it took no advantage of linguistic redundancies, and the question arose as to whether the intelligibility of its output for English text could be improved by a simple computer program that would take into account some of the constraints of the language. Degarbler is an IBM‐7090 program, developed by (Mrs.) C. K. McElwain, that at least partly corrects English text as it might be corrupted by a noisy Morse code channel and MAUDE decoding. The linguistic information utilized by the program is restricted to a knowledge of vocabulary and a table of the Morse‐code equivalents of the alphabet and the numerals. As the program now stands, it corrects between 64% and 74% of the garbled words of messages having a 3% to 9% letter‐error rate. Qualitatively, the results appear better than the percentages indicate. The program accepts very nearly unintelligible text and renders it easy to read.

ISSN:0001-4966    

DOI:10.1121/1.1937171

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The frequencies of fundamental and overtone resonance in a thickness‐mode piezoelectric resonator depart from an integral multiple relationship when the electromechanical coupling of the resonator material becomes large. This behavior can be explained by the fact that large electromechanical coupling significantly lowers the resonant frequency of the fundamental mode with respect to the overtones. The resonant frequencies have been calculated as a function of the electromechanical coupling coefficient and the mode number for thickness modes in poled ceramics. (The theoretical analysis for thickness‐mode resonators is given in a separate paper by Tiersten.) The measured resonant frequencies of both thickness‐dilatational and thickness‐shear mode resonators made fromBaTiO3, PZT‐5, and PZT‐7 ceramics were found to show good agreement with theory. An important practical application of this anharmonicity is in the determination of the shear coupling coefficientk13, direct measurement of which has hitherto been difficult. This coupling coefficient, along withk33andkt, can now be obtained from the ratios of the resonant frequencies of the fundamental and overtone modes.

ISSN:0001-4966    

DOI:10.1121/1.1937174

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The electromechanical coupling coefficientkis usually derived from the difference between resonance and antiresonance frequenciesfRandfAof a particular mode obtained from observations of the maximum and minimum values of electrical impedance. A simple relationship betweenfR,fA, andkexists only when the mechanicalQis infinite and the electrical losses negligible. This relationship breaks down whenk2Q<2, a region which is important since the minor modes of barium‐titanate transducers may haveQvalues of several hundreds andk<10%. For example, it has been found that, with 4

ISSN:0001-4966    

DOI:10.1121/1.1937177

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Ten ear‐protective devices—three plugs, three muffs, two phone‐in‐muff combinations, one phone‐in‐muff in protective helmet, and one plug‐muff combination—were tested for noise attenuation. The psychophysical method of binaural threshold shift (occluded ears minus open ear) for half‐octave bands of noise using three trials on five experienced listeners was used. When averaged over all frequencies at half‐octaves (60–8000 cps), the V‐51R plug under a Willson sound‐barrier muff gave the best attenuation; the Sharpe HA‐10 earphone, the Willson sound‐barrier muff, and the David Clark 372‐HPF muff gave almost equal and the next best attenuation; the Zwislocki resonant plug showed only slightly less attenuation than the three muffs; the V‐51R and ComFit plugs were nearly equal with somewhat less attenuation than the Zwislocki resonant plug; the Gentex helmet and Telephonics sonibar muffs (with sound‐powered phone and without) were the least effective attenuators of noise. Only in the frequency range from 60 to 300 cps were plugs better than the better muffs. All devices gave more attenuation as the frequency region increased from low (60 300 cps), to medium low (300 1000 cps), to medium high (1000–2900 cps), to high (2400–8000 cps), except for the Zwislocki resonant plug in the high‐frequency region. The effect of sealing ring, headband pressure, and volume was experimentally studied independently of the actual devices tested. Flow‐resistance measurements were made to explain the combined effects of headband pressure and seal around the ear.

ISSN:0001-4966    

DOI:10.1121/1.1937185

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP