Effect of Measurement Set-Up Characteristics on Sound Scattering of Pyramid-Based Diffusers
Mallory Morgan, Vassar College ’17, Ian Kowalok, Vassar College ’16 and Prof. David T. Bradley with Consortium for Faculty Diversity Post-Doctoral Fellow Kim Riegel
A uniform sound field is desirable in acoustically sensitive spaces such as concert halls and recording studios. Planar surfaces such as walls produce strong directional sound reflections, causing local variations in sound pressure. A diffuser is a non-planar surface that mitigates the effects of strong reflections by scattering sound in many directions. The effectiveness of a diffuser is indicated by the diffusion coefficient, a quantifier used to characterize the spatial uniformity of the sound it reflects. ISO standard 17497-2 outlines a method for measuring the diffusion coefficient, but fails to specify certain measurement set-up characteristics that may have an effect on resulting data. The diffusion coefficient of a surface with a pyramid-based repeating pattern has been measured while varying four measurement set-up characteristics. The first measurement parameter was pattern orientation. Two wooden surfaces with a circular perimeter were measured, the first with full pyramids at the diameter and the second with the pattern shifted to result in partial pyramids at the diameter. The second measurement parameter was surface material. The first wooden surface was compared to an identical ceramic surface created using an additive 3D-printer technique. The third measurement parameter was surface perimeter shape. The ceramic surface with a circular perimeter was compared to a ceramic surface with a square perimeter. The final parameter measured was surface height relative to the measurement platform. The ceramic surface with a square perimeter was measured at three different heights: with the low point, mid-point, and high point of the pyramids flush with the measurement platform. The results and analysis of the measured data will be presented. It is anticipated that the collected data will result in the clarification and possible revision of the ISO standard. This material is based upon work supported by the National Science Foundation under Grant No. 1055268.