Pseudorandom sequences for binary amplitude diffusers.

Abstract

Binary amplitude diffusers create a mixture of absorption and diffusion and are used to improve room acoustic conditions. They require a two dimensional binary pseudorandom array to state where absorbing and reflecting patches should be. Consider the binary array to have dimensions A×B. Ideally, A and B should be similar to maximize performance. Such an array can be produced by folding a one dimensional sequence into a two dimensional array using the Chinese Reminder Theorem. This theorem requires A and B to be coprimes. However, there is a limited set of optimal one dimensional sequences that can be generated from number theory with suitable length AB. In the past maximum length sequences have been used because they display desirable autocorrelation characteristics, but their period is 2m−1, where m is an integer and so there is a limited number available. Consequently, it is necessary to examine other ways of generating optimal two dimensional arrays. This paper looks into other number theoretic sequences, and other construction techniques for forming binary arrays. The suitability of these for constructing two dimensional binary amplitude diffusers is examined. Boundary element modeling is used to evaluate their performance.