A review of diffusor design over the past two decades.

In the later 1970s Manfred Schroeder suggested using number theory sequences to approximate uniform angular scattering. Today tens of thousands of these diffusors are in use in almost every type of architectural acoustic application. Schroeder's work has been a catalyst, enabling the design of numerous new diffusor types. D'Antonio employed additive modulation, in the form of a self-similar fractal diffusor to minimize the lobing associated with periodic arraying and to extend the frequency bandwidth. Angus suggested multiplicative spread spectrum modulation and orthogonal modulation to minimize lobing. Angus has suggested binary reflection-absorption amplitude gratings, which D'Antonio has used for 2-D planar binary amplitude diffusors. Cox used numerical optimization and boundary element prediction techniques to optimize the performance of number-theory diffusors, stepped diffusors, curved and fractal shapes. Cox and D'Antonio are developing optimized aperiodic shapes to form aesthetically pleasing diffusing acoustical sculpture. Shape optimization has significantly expanded the choice of available diffusors. Today, diffusors can be designed for a specific appearance, specified scattering coverage, given source and receiver positions and a desired frequency bandwidth. All of these surfaces developed over the past two decades comprise an expanded palette of scattering surfaces. These complement contemporary architecture in the way that statuary and relief ornamentation blended with classical architecture. [ABSTRACT FROM AUTHOR]