残響測定について(第2報) : ピストル音の解析

抄録

Explosive pulse waves produced by a pistol shot were photographed by the Schlieren method. They consist of 3 or 4 wave surfaces and the duration of one wave is about 10 micro-seconds. Theinterval of each wave front is about 100 or 200 micro-seconds. Their propagation velocity seems to become normal at one milli-seconds after explosion. But the waveform of the pulse is different when we observe it through the electro-acoustical instruments such as a microphone, an amplifier and a cathode-ray oscillograph because it is dependent on the frequency characteristics of the measuring system. The photographs obtained in this case showed that only one wave was predominant and the duration of this pulse was about a few hundred micro-seconds. Flutter echo in a straight tube generated by a recorded pistol shot was observed. The frequency components of a series of pulse waves of equal were obtained experimentally and theoretically. When the pulse duration time τ is adequately smaller than the time interval between reflected pulses T, following result is obtained by Fourier's integral. a(ν)=(P0/π)[sin( πντ)/πν][1/2+cos2πνT+cos2(2πνT)+..+cos n(2πνT)] (2n+1) is the number of pulses under consideration. If the observation is made by the instrument whose frequency response is R(ν), then the frequency component will be a(ν) R(ν), and the wave from is expressed as P(t)=∫^∞ -∞ a(ν) R(ν) exp(-2πiνt)dt The relation between the peak level of the pistol shot observed in the reverberation measurement and the writing speed of the recorder was measured by means of a high speed level recorder. The experiments on 20 shots showed that the deviation of peak level was about 2 db and was independent of the writing speed.