Measuring the uniform diffusion coefficient: Synthesized aperture goniometer measurements.

Abstract

There are currently two methods to measure the diffusion/scattering from acoustical surfaces: reverberation chamber measurement and in-situ measurement using a semicircular array of microphones called a goniometer. Each of these methods has advantages and drawbacks. The reverberation chamber method accounts for random incidence, but produces inconsistent results for materials of the same profile but different absorption. It does not distinguish between one-dimensional and two-dimensional surface topologies, since the sample is rotated, and is also inapplicable to high absorption materials. The goniometer measurement quantifies directivity as well as diffusion, but presents challenges related to processing power, as many microphones are required to achieve reasonable resolution. Using a procedure akin to synthesized aperture radar, a 2.5° resolution polar plot of the 180° response is achieved by scanning eight microphones rather than employing a full array of 72. Also, since the direct sound and reflected sound arrive at the receiver in close succession when measuring low incident angles, special processing must be exercised in order to resolve the relationship between the sounds. This research addresses the challenges of the goniometer measurement and attempts to use a synthesized aperture goniometer to derive accurate diffusion and directivity properties of materials.