Sound fields caused by diffuse-type reflectors with periodic profile

Abstract

For the purpose of providing highly diffuse reflections, the reflection surface with periodic roughness has been often used. The degree of diffusion of this type can be evaluated by an objective measure DNSD proposed by the author. Optimum diffusers with periodic profile can be designed by using this measure, but this type of diffuse reflections might have some aspects of misgivings due to its periodicity, which may be a kind of so-called "tone coloration." In other words, highly diffuse reflections might have a problem of some particular effect on the spectrum caused by interference between the direct and the reflected waves, which might be different from an ordinary case of the plane surface. In this paper, to clarify the physical properties and the mechanism of diffusion caused by periodic-type diffusers, SPL characteristics and impulse response of the reflected field as well as the scattering performances for three types of reflectors are discussed including the measured data from 1/8-scale model experiments. As a result of detailed discussion on the relation between the surface profile and the incident wave, the effect of periodic roughness on the reflection is revealed quantitatively.