球殻音源による音波のひずみ

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It is well-known that a sound wave of finite amplitude changes its wave form as it propagates in a medium ; and consequently sounds of extraneous frequencies are generated. This sound distortions are caused by the nonlinear nature of air. In this paper, the magnitudes of sound wave distortions produced by a spherical sound source which was proposed as a standard for free field measurement (Fig. 1) are investigated. A standard source requires a greater acoustic power, which in turn requires an increased intensity of the source. Consequently the amplitude of the sound wave around the source becomes finite, so the problems on the distortion of wave by a spherical sound source arise. In analyzing this problem, a formula for the distortion factors of sound pressure which seem to be significant from the observational points of view and are defined in terms of the effective pressure ration of the second harmonic to fundamental has been derived (Eq. (16)). In particular, the Eulerian coordinates are used and the effects of viscosity and heat conduction are neglected. Next, in accordance with this analysis are calculated the distortion factors for the case where the piston of the source is sinusoidally vibrating in Lagrangian sense (Eq. (17)), and several examples are shown in Figs. 2〜5. From these numerical results, it is shown that the distortion of sound pressure is considerably influenced by the variation of observation points and the magnitude of the area of piston.
社団法人日本音響学会の論文
1974-04-01

球殻音源による音波のひずみ

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