Effect of measurement conditions on sound scattered from a pyramid diffuser in a free field

Abstract

A surface with a non-planar geometry, referred to as a diffuser, can be used in acoustically sensitive spaces to help control or eliminate unwanted effects from strong reflections by scattering the reflected sound. The scattering behavior of a diffuser can be measured in a free field, according to the standard ISO 17497-2. Many of the measurement conditions discussed in this standard can have an effect on the measured data; however, these conditions are often not well-specified and/or have not been substantiated. In the current study, a pyramid diffuser has been measured while varying four measurement setup parameters: surface absorption coefficient, surface perimeter shape, surface vertical mounting location, and surface pattern orientation. Reflected polar response data have been measured, analyzed, and compared for various conditions of each parameter. The absorption coefficient showed the most significant difference in the polar response plots. The vertical mounting location produced some variation in the data, with the average mounting height location shown as the optimal setting. The surface perimeter shape shows no variation in the polar plots. The surface pattern orientation also showed almost no difference in the measured data.