The Role of Reflection Phase Grating Diffusors in Critical Listening and Performing Environments
In critical listening and performance environments, acoustical energy reaches an observer via direct and indirect reflection paths from surface boundaries. When the indirect energy arrives via specular reflection, all of the acoustical energy from a given source arrives at a single instant in time, from one point on the surface. If this same amount of energy is backscattered from a reflection phase grating (RPG) array, the energy is temporally distributed and all surface elements have an energy component in the observation direction. The temporal energy distribution minimizes broadband anomalies formed by the combination of a few discrete reflections having slightly different reflection paths and gives rise to a rich, dense and non-uniform comb filter response, which produces a psychoacoustically pleasing ambiance. Specular energy is directed into a fraction of half-space determined by the source location and size of the specular surface, whereas, backscattered enrgy from a one-dimensional RPG diffusor is distributed into a hemidisk covering half-space. We will examine the differences between specular reflections and a diffuse sound field created with RPG diffusors. Both experimental TEF measurements and theoretical calculations, using a new near-field computer program based on Kirchhoff diffraction theory, will be presented. Performing Arts and Recording/Broadcast applications will be discussed.
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