衝撃パルス(ピストル)によって発生する音響

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Acoustic measurement by pulse sound such as pistol shot or electric discharge has been reported by W. Schindelin, G. V. Bekesy and V. W. Weber. Recently, as reverberation and transmission measurements it has become common method. Merits of the pistol shot are considered to be, the first, it produces great sound pressure and large signal to noise ratio can be obtained, the second, it is very simple and any complicated system such as, amplifier and oscillator are not necessary and with the aid of a frequency analyser, the measurement covers over audible frequency range, the third, it is possible to detect the individual pulse caused by reflection and it is suitable for the measurement of percent disturbance in room acoustics. Author obtained fairly reliable results about the reverberation time of several theatres by pistol as the sound source. Pistol shot is the phenomenon of short period and the produced sound is a transient one. Some results of peak presure level, time duration and the spectrum of the pulse have been reported by several authors but farther study is necessary. Shock wave produced by a pistol shot was observed by Schlieren method. It has complicated structure but the wave front reveals spherical propagation. Results of photometry show that the duration of the first wave front is the order of 10μ sec. When we observe pistol shot, the quality of pulse will be deformed owing to the frequency characteristics of our ear or microphone system. Particularly, the frequency response of microphone affects the wave shape considerably. By several types of microphones, the different shapes of the direct waves were observed, but a microphone that had sufficient sensitivity for high frequencies such as 10kc or more, followed to the wave form fairly well, and asymmetry of the positive and negative waves similar to the results of photometry were observed. Reverberation of the pulse produced by pistol is the series of pulses and reverberation curve is their envelope. If the duration of pulse by pistol is only 10 μ sec, the sequence of reflected pulses must be separated ones. Flutter echo in closed long tube was photographed by broun tube escillograph and the frequency spectrum was measured by electric filter. The spectrum of the series of pulses depends not only to the pulse width but the time intervals of the successive pulses. Theoretical calculation explaines the expreimental results fairly well. Reverberation of pulsed sound in three dimentional room is very complicated phenomenon, especially in irregular shaped room, the frequency spectrum by series of pulses can not be analysed theoretically, then the distribution of reflected pulses and the spectrum were measured experimentally in reverberation chamber. As the source of sound for reverberation measurement, pistol shot is very simple and convenient method and the measured results of reverberation time were compared with those observed by another source such as thyratron noise. We can not find any difference between them, but pistol is rather advantageous than any other sourses because of large s/n ratio during measurement. Eyring's reverberation formula can be introduced from the results of pulse statistics analysis and the attenuation of divergent spherical waves. For appendix the error produced by writing speed of the recording system to the results of reverberation time was estimated, and the tentative recommendation for the determination and expression of the reverberation characteristics were also described.
宇宙航空研究開発機構の論文
1957-12-05

衝撃パルス(ピストル)によって発生する音響

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