Abstract
In this study, the author has performed a model test to clarify the sound effect by diffuser, which is often used, as one of the various methods which are employed in practising an acoustical designing to diffuse the sound field in an auditorium of other. The reflective rooms were adopted as model rooms, which are 4.08m×2.85m×2.2m in dimensions and 0.8m×0.75m×0.43m, that is, one fifth of the former, respectively. As diffusing elements, a triangular and a semi-cylindrical diffuser were adopted for the former room, and the latter, for which a triangular, a cylindrical, and a partially spherical diffuser were used. As to the latter room, a measurement has been made to clarify the effect when the uniform absorption properties was given to the surfaces of the interior, and for that purpose, sheets of paper and cotton cloth wered sticked on them. The diffusing effect has been shown as the irregularity of the reverberation curve by pulse in terms of δp and Ld, as in the following, δp; mean fluctuation of the difference of peaks and dips during the time when the value at a point on the reverberation curve has decreased by A dB. Ld; ratio, in percentage, of the length of the curved part, to that of the linear one, between a certain distance on the reverberation curve. The results of the measurement could be briefly stated as follows, (1) In descending order of the diffusing effect are spherical diffuser, polycylindrical diffuser, and triangular diffuser. (2) The more the number of the walls with diffusers attached, the more favorable is the effect. (3) The relations between the location of a sound source and that of a diffusing wall are not distinct. Therefore, their mutual locations are required to determine on the geometrical principles of acoustics. (4) The irregularity of a reverberation curve can be improved by increasing the absorption properties. (5) To give the properties of the absorption of low frequency to the surface of a diffuser, produces a like effect with the increased dimention of it. (6) The diffusing parts of walls are required to amount to some 50 or 60% of the whole to obtain a sound field in a rectangular room.
