Experimental evaluation of the backscattered polar response of sound absorbing, reflecting, and diffusing materials

Abstract

The sound that we hear in a room is a combination of the direct sound and indirect reflected sounds from room boundaries. Because the amplitude, directionality, and temporal distribution of the indirect reflections affect how one perceives the actual sound source, control of room reflections using absorption, reflection, and diffusion is a central consideration in acoustical design. Effective application of these ingredients is based on an understanding of the backscattered directional response for a given angle of incidence, angle of observation and frequency, i.e., the backscattered polar response. To evaluate the experimental polar response a testing technique using time delay spectrometry was developed [P. D'Antonio and J. Konnert, AES Preprint 2295, 79th AES, New York (October 1985)]. The method allows the evaluation of the backscattered frequency response of a sound modifying material mounted on the boundary surface at any scattering angle, for a given angle of incidence. For sound absorbing materials, for example, these “directional” scattering coefficients augment the traditional random-incidence ASTM reverberation chamber data. The technique will be described and polar response data for sound absorbing, reflecting, and QRD® diffusing panels will be presented. An alternative method using sound intensity will also be discussed and preliminary data presented.