Acoustic phase gratings for reduced specular reflection

The use of acoustic phase grating surfaces, Schroeder diffusers, to attenuate specular reflections has been investigated. The concept of primitive root diffusers is reviewed and developed. Some guidelines for proper design are given, and the limitations of the diffusers identified. A modification to the primitive root sequence is suggested which results in a null in the specular reflection direction at multiples of the design frequency. This improves the performance of the phase gratings particularly for modulated periodic arrangements. The use of optimisation to achieve better broadband notch diffusers is detailed.