各種マイクロフォンの特性に關する研究(其の二)指向特性

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In the preceding paper on the same subject, the amplitude and frequency characteristics have been investigated in detail. As the continuation of it, the present paper deals with the directional characteristic. As the source of sound, the cone speaker of a moving coil type was excited by the valve oscillator of variable pitch. During the experiment, its radiant energy was measured continually by the Rayleigh disc set in front of the source, its distance from the source being more than 50cm. The microphone under test was made to rotate horizontally and could be set at any angle to the ray of sound. The amplitude of sound received through the microphone was measured by the microammeter with the aid of a resistance-capacity amplifier. In our experiment, the distance between the source and the microphone was kept more than 3 metres, otherwise the standing wave appeared between them. The experiment was performed in the perfect sound-proof chamber. As the results of experiment, the directional characteristics of a condensor microphone, a ribbon microphone, a Reisz carbon microphone and a piezoelectric microphone as the function of frequencies are shown respectively in Fig.2, Fig.6, Fig.7 and Fig.10.
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