摘要:

Equipment has been developed for the direct measurement of the attenuation of short pulses of audiofrequency sound in the open. The source consists of a 500‐cycle, one‐quarter wave pipe which is excited at intervals of about 10 sec. by an explosive mixture of acetylene and oxygen. The damped sound wave thus produced is first received by a near reference microphone and after an interval of time at a second distant microphone. Appropriate calibration and timing circuits are provided to actuate a single sweep oscilloscope as the sound pulse passes each microphone. The signal from the distant station is returned to the near station by f‐m. Both signals are recorded automatically by a solenoid operated camera. A second oscilloscope and continuous film camera provides accurate transit time records. By observing the reduction in sound intensity between the two stations and making correction for the divergence of the sound wave, the attenuation is computed. The values thus obtained are compared with those calculated from laboratory measurements under similar temperature and humidity conditions.

ISSN:0001-4966    

DOI:10.1121/1.1917041

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

When a sound enters the ear it sets up a vibration pattern along the basilar membrane. This vibration pattern initiates nerve pulses which travel along the eighth nerve to the brain, where a second pattern of neural activity results. Two general methods may be used to study these patterms: (1) the objective measurement of cortical potentials by the electro‐physiologist, and (2) subjective measurements such as masking and fatigue effects. The present paper is based on the latter procedure in which the results of loudness and fatigue tests have been combined to give patterns of cortical activity in terms of millisones per kappa‐band. Use of fatigue patterns permits employment of a low level probe tone which overcomes the difficulties formerly experienced with artifacts in masking patterns due to beats and distortion products.

ISSN:0001-4966    

DOI:10.1121/1.1917047

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Equipment has been built for measuring vibratory displacements of very small mechanical elements such as phonograph styli and piezoelectric crystals. It employs a probe of small dimensions so that virtual point measurements may be made. The probe does not contact the point under measurement and therefore imposes no mechanical load. The variation in capacitance between probe and vibrating surface is used to measure the displacement. Through the use of a built-in calibrator, the sensitivity may be adjusted electrically for direct meter reading of vibratory displacement without resorting to precise adjustment of condenser plate spacing. Displacement amplitudes of less than 10−6cm may be measured. The output signal corresponds accurately to the displacement both in magnitude and in phase over a wide frequency range, so that complex vibrations are portrayed accurately on a cathode-ray oscilloscope. The equipment has been calibrated by four independent methods, including a reciprocity method, with close agreement.

ISSN:0001-4966    

DOI:10.1121/1.1917053

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The published data concerning differential sensitivity of the ear to changes of frequency and intensity have been studied, assuming the applicability of widely held views of the hearing process. The present analysis provides an additional method for correlating the position of maximum stimulation on the basilar membrane with the frequency of a tone which produces that stimulation.

ISSN:0001-4966    

DOI:10.1121/1.1917059

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The “long corridor” referred to is actually a mechanical transmission line in the form of a helical spring. Compressional waves in the audiofrequency range are sent down the spring by an electromechanical driver and received at the far end by an electromechanical pick‐up. Reflection occurs at each terminal allowing standing waves to build up. Oscillograms have been obtained for frequencies below 100 cycles, showing the discontinuous nature of the “reverberation” which is produced in such a “long corridor.” Eyring's mechanism, using image sources, is shown to fail to explain the oscillograms. A new mechanism is presented which seems to explain all cases, including that of non‐normal modes.

ISSN:0001-4966    

DOI:10.1121/1.1917062

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Attenuation measurements made in solutions containing the principal inorganic constituents of sea water indicate that the absorption in frequency range below 400 kc is due primarily to the salts in solution and not to marine life. It is further indicated thatMgSO4plays a dominant role in the observed absorption.

ISSN:0001-4966    

DOI:10.1121/1.1917067

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP