1957 年 13 巻 4 号 p. 320-327
The effects of the shape and volume of the reverberation chamber on the measured absorption coefficient are discussed here. Reverberation chambers used for this research were two chambers in our institute, which were constructed in the same manner except for the shape and the volume. Same test specimens and measuring apparatus were used in this research, making it possible to investigate purely the effect of the shape and volume of the chamber. At first, the absorption coefficient of test specimen was measured in chamber No. 1 (volume 513 m^3, non-parallel walls). In this case, it was independent to the position of microphone and test specimen, as reported earlier. On the other hand, in the case of chamber No. 2 (6 m×4 m×5 m, rectangular parallelopiped), it was shown that the absorption coefficient was affected appreciably by these measuring conditions, especially for large absorption. Thus, in some cases, the absorption coefficients measured in both chambers differ from each other. Only under the specially selected measuring conditions, the absorption coefficient coincides fairly well, in general, the coefficient by chamber No. 2 is smaller than that of chamber No. 1. By considering the behavior of sound waves in both chambers, it is concluded that the shape of the reverberation chamber plays an important role for the uniform distribution of sound energy. As to the absorption coefficient defined by Sabine's formula, is should be the coefficient which is unaffected by the position of microphone and test specimen. When such a phenomenon as shown in chamber No. 2 occurs in the reverberation chamber, it is necessary to be careful of the measuring conditions; or else it would lead to erroneous results if the mean value of absorption coefficient is simply taken on several microphone position.