摘要:

The high‐frequency calibration of a plane disk hydrophone of large diameter by the usual plane‐wave reciprocity method is a difficult task, requiring a large anechoic tank and precise mechanical alignment gear. A new and absolute calibration technique utilizing the radiation pressure of a standing wave system is described. The calibration curve of a barium titanate hydrophone of diameter 1.5 in. and of resonant frequency 1.0 mc is presented over the frequency range of 300 to 5000 kc.

ISSN:0001-4966    

DOI:10.1121/1.1908528

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The shock effect of a terminal‐peak sawtooth of acceleration obtained by a drop onto a lead pellet has been investigated experimentally using the shock spectrum as the criterion of severity. It is shown that this spectrum obtained by analysis of the acceleration‐time data can be made to approximate closely over a wide frequency range that obtained theoretically for an ideal sawtooth. The smoothness of the spectrum which results from the extreme asymmetry. of the pulse shape makes the sawtooth particularly attractive standard pulse shape for shock test in the laboratory.

ISSN:0001-4966    

DOI:10.1121/1.1908530

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Existing passive materials are inadequate to cope with many problems in the control of noise, vibration and reverberation. It is only within quite recent times that active systems have been given consideration for the control of sound. The electronic sound absorber is an example of an active‐type sound absorber. The electronic sound absorber consists of a microphone, amplifier, and loudspeaker connected in an inverse feedback manner. The electronic system reduces the effective acoustical impedance in the vicinity of the absorber. As a consequence, the electronic sound absorber may be used in the manner of a conventional sound absorber or as a zone‐type sound reducer. The electronic vibration reducer consists of a sensor, amplifier, and driver connected either in negative or positive feedback fashion. The electronic vibration reducer may be used to isolate vibrating machines or to reduce the vibration of machines.

ISSN:0001-4966    

DOI:10.1121/1.1908532

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The noise canceling effectiveness of a microphone is determined by measuring the random noise discrimination as a function of frequency under conditions simulating actual usage, and then using this characteristic to compute the articulation index for an ideal system containing the microphone, when operating under specified noise and speech conditions. Results so obtained are shown to correlate with those of articulation tests for three microphones evaluated for three noise types at different noise levels.

ISSN:0001-4966    

DOI:10.1121/1.1908534

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A theoretical and experimental investigation is made into the mechanism of noise in magnetic media as used in magnetic recording. It is shown that the basic noise in a wow and flutter free system arises from the fact that the domain size in metals or the particle size of oxides is finite, and improvement in the lower limit of noise can only be made by reduction of particle or domain size. The effect of impressed ac and dc magnetization on the noise level is also examined.A theoretical value for the tape noise arising from the particle nature of an oxide medium has been derived by taking into account the modern theories of magnetism of the iron oxides and evaluating exactly the mathematical functionf(x) which appears in the noise equation. Good agreement with the observed noise voltage is obtained.It is also shown that the basic wide‐band unmagnetized tape noise level of 0.6 μv for the head employed is extremely low and that for the ideal system the theoretical signal/wide‐band unmagnetized tape noise ratio is independent of tape velocity and varies as the square root of the track width.

ISSN:0001-4966    

DOI:10.1121/1.1908536

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Reverberation chamber measurements are presented for resonant absorber constructions covering a range of resonant frequencies. Types of constructions tested were (1) thick layers of porous material covered by the facing and backed by a hard wall and (2) facings covered with a resistive cloth layer and mounted with air space backing. Measurements were made with thicknesses up to1412 in.behind the panel to secure high absorption at low frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1908537

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1908539

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP