摘要:

Translation of sound into visible patterns is discussed in terms of broad objectives. It is suggested that no single design can be optimum and that perhaps the most useful standard of reference is the human ear. Special interests and complexity generally affect final design requirements.

ISSN:0001-4966    

DOI:10.1121/1.1906464

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Five thousand tons of high explosives detonated on Helgoland, April 18, 1947, created air pressure perturbations recorded on microbarographs between 66 and 1000 km SSE from the blast. Instruments responded to frequencies 0.05–5 c.p.s. Arrival times of abnormal signals at six stations more distant than 220 km, supplemented by high altitude meteorological data and the assumption of negligible winds above 30 km, permit upper atmosphere temperature calculations. Temperatures agree with N.A.C.A. values up to 42 km, but show a reduced gradient above that altitude, and a maximum value 294°K in the temperature hump between 30 and 70 km. This temperature maximum establishes critical ray which is refracted to infinity. A new explanation for observed outer boundaries of abnormal zones is therefore proposed, and substantiated by recorded evidence of dispersion near the temperature maximum. In the signal received near the abnormal zone outer boundary, high frequency content predominates.

ISSN:0001-4966    

DOI:10.1121/1.1906471

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A one‐dimensional theory of operation of the double crystal acoustic interferometer is presented. The theory is sufficiently general to include both resonance and off resonance operation and any amount of acoustic loading of the crystals. The effects of holder losses and electrical loading of the receiver crystal are also included. A relation is developed which can be used to obtain values of the acoustic velocity and absorption coefficient of the coupling medium from the experimental measurements.

ISSN:0001-4966    

DOI:10.1121/1.1906463

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Some aspects of the theory of low loss crystal systems are presented. The effect of small losses on the resonant frequency, the difference between the resonant and antiresonance frequencies, and the electrical impedances at resonance and at antiresonance, is calculated. A quality factor is defined and related to the mechanical loads on the crystal.

ISSN:0001-4966    

DOI:10.1121/1.1906465

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The application of the Laplace transform to the general problem of the beam is discussed. The method requires no knowledge of normal modes often employed in the classical solution. A solution in closed form is given for the forced vibration of a hinged beam excited by a concentrated harmonic force. The result converges to the correct static curve for zero frequency. The method is extended to the problem of finding the natural frequencies of beams with concentrated mass and spring. The analysis for beams with several masses and springs is outlined.

ISSN:0001-4966    

DOI:10.1121/1.1906466

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906468

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906469

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The results of measurements of sound absorption by the body surface of man and fur‐bearing animals are reported for the frequency range 100 to 12,000 c.p.s. The acoustical impedances and the absorption coefficients of the surfaces were determined from the resonance characteristics of an air‐filled tube. The end of the tube was closed first by a rigid wall and then by the unknown surface. From the change in the resonance characteristic induced by the unknown surface the desired quantities were calculated. In order to speed up the measurements, which is important with living test material, a second method was used. In this method the air column was excited by sound pulses, and the decay time of the sound pressure was measured from the photographs of the cathode‐ray trace. At the higher frequencies an aluminum rod, pressed against the body surface, replaced the air column. The desired quantities were calculated from the change in longitudinal resonance characteristics in a manner similar to that employed for the air column. The absorption coefficient of the human body surface varies frown 10 percent to 0.1 percent and decreases at higher frequency. The resistances per cm2varies between 103and 105ohms and are dependent upon the area of application and the pressure upon the skin and muscles. The measurements on rats show that up to 1000 c.p.s. the absorption coefficient decreases and then increases up to 6000 c.p.s. The behavior below 1000 c.p.s. is determined largely by the tissues beneath the skin while the increased absorption above 1000 c.p.s. is the result of the presence of the fur. This is demonstrated by measurements on shaved animals where the absorption decreases steadily as the frequency increases, whereas in the case of furred skin supported on a rigid wall the absorption increases as the frequency increases. These absorption coefficients permit the estimation of the sound energy absorbed by a whole animal. The sound intensity required to cause heat death can then be calculated approximately.

ISSN:0001-4966    

DOI:10.1121/1.1917027

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A study is being made of sound transmission of walls, doors, and panels at the Riverbank Acoustical Laboratories with the purpose of relating the measurements more closely to the properties of the test wall alone, instead of the test wall plus the adjoining rooms. The possibility is being investigated of measuring the effective “impedance” of a wall with random distribution of incident sound. This method is similar to that used at Harvard in tests on small airplane panels for sound at normal incidence. In order to allow for phase differences in the motion of the test wall, measurement of the transmitted sound is to be made at a distance from the wall in a long narrow room with one end covered by absorbing wedges. To evaluate test conditions, the sound fields have been explored on either side of a test wall. Pressure distribution on the source side (reverberation chamber) of the wall is given as a function of frequency and reflector position. This also indicates the state of “randomness” in the reverberation room. Results are also given for preliminary tests on the transmitted sound field.

ISSN:0001-4966    

DOI:10.1121/1.1917030

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Comparison is made of the response of a number of earphones measured on several types of earphone couplers. Points of difference are noted and the attempt made to explain them through the use of some specially designed couplers. Certain characteristics were observed which might influence the design and use of couplers for purposes of determining earphone response.

ISSN:0001-4966    

DOI:10.1121/1.1917036

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP