Abstract
To have echoes from rear wall in the auditorium is one of the worst acoustical condition, therefore, in order to prevents these echoes many kinds of such diffusers as polytriangular, polycylindrical, or spherical diffuser are used. This paper reports the measurements of echoes from rear wall using the model and accomplishes a method to find out the suitable shape and size of these diffusers. The scale of model was 1/10 and it has a width of 180cm and a hight of 30cm. The shapes of the model walls were a kind of flat and two kinds of curved surfaces of R=5m and 2.5m. The shape of diffusers which were fitted on these walls were twe kinds of polytriangular diffusers (with width of 18cm and depth of 1.8cm and 2.7cm) and one kind of polycylindrical diffuser with width of 18cm and depth of 2.7cm. The frequency which was used in this investigation was 1.25kc〜40kc and the cone type tweeter was used as sound source for low frequency (1.25kc〜10kc) and condenser speaker for high frequency (10kc〜40kc). The microphone was condenser type for all over the frequency range. The results of these experiments were as follows. 1. At the low frequency (below 2kc) diffusers which were fitted to the walls were not effective. 2. In the middle frequency range (about 2kc〜10kc) the diffusers were effective. 3. At the high frequency, plane surface of every triangular diffuser reflects sound regularly, and large echo was found at the side area of the wall.
