SOUND FIELDS AND SUBJECTIVE EFFECTS OF SCATTERING BY PERIODIC-TYPE DIFFUSERS

Walls and ceilings with quasi-periodic unevenness have often been designed to provide diffuse reflections. As for the shape and the size of this unevenness, with the help of some statistical treatment, it is possible to design effective diffusers with an intended directional pattern; this has great merit in sound fields with respect to spatial aspects. In addition to this spatial property of diffusion, reflection from the surface should not have particular response characteristics that may have a serious effect on our subjective experience. A well-known problem is “colouration” caused by interference between direct and reflected waves, which might create an odd tonal distortion in the case of a surface with periodic unevenness. This may be the reason that creating a periodic series of reflections at the receiver is generally avoided. Two issues need to be addressed: (1) is a periodic structure of reflection a major obstacle in practical use? and (2) to what degree is structural repetition acceptable? Clarification of these matters is necessary in order to design effective diffusers for practical applications. This study examines the physical properties of, and the subjective effects of tonal response to, sound fields caused by scattering from periodic-type diffusers.