Abstract
In this paper, several problems concerning the absorption coefficient measurements are mentioned. The new reverberation chamber No. 1 (Volume, 513 m^3; reverberation time at 500 c/s, 22 sec) was used for this research. The test sample used are fibrous acoustic tiles and mineral wool. These materials were selected from the commercial acoustic materials according to their frequency characteristics of absorption coefficient. The following results were obtained: (1) Decay curve shows nearly perfect logarithmic decay even when the test materials are present. (2) Absorption coefficient of test materials was unaffected by the position of the microphone for the sample area ranging from 10- m^2 to 30 m^2. (3) For the sample area 10 m^2, absorption coefficient was not dependent on the position of the test materials. There results seem to confirm the presumption of model room experiments (previously reported). In closing the accuracy of absorption coefficient measurements is discussed. It is stated that, in this chamber, the variation of repeatedly measured decay curves is very small and the reverberation time is scarcely affected by the observers. Thus, it is possible to measure the absorption coefficient with relatively small test materials.
