Effect of Reverberation Chamber Parameters on Sound Field Diffusivity
Craig Pellegrino ’18, Noah Snider ’18, Robert Elizardo ’20, and David Bradley (Physics)
A reverberation chamber is a room used to create a sound field with a high degree of diffusivity—one which is both homogeneous (with properties that are independent of position) and isotropic (with properties that are invariant with respect to direction). To achieve sound field diffusivity, reverberation chambers are typically equipped with wall-mounted panels to distribute the sound energy more evenly. These chambers provide an adequately diffuse sound field that is the ideal setting to measure the acoustic properties of an object, such as the amount of sound energy the object absorbs or scatters.
The goal of this project was to qualify the reverberation chamber in the Vassar Acoustics Research Laboratory (VAR-Lab) according to the standards set forth by the International Organization of Standards and ASTM International. Measurements using a weighted sine sweep signal were taken with three loudspeaker positions and four microphone positions. The effect of the signal length, microphone and loudspeaker positions on sound field diffusivity measurements was investigated. In addition, the backs of the wall-mounted diffuser panels were dampened with acoustic putty, and the optimal amount of dampening was researched. The ideal number of diffusers was also investigated. After achieving a highly diffuse sound field and successfully qualifying the chamber, different mounting techniques of commercially available diffusers were tested to understand how the type of mounting affects their absorptive behavior. It was found that on average, diffusers that were sealed to the floor with putty absorbed less sound energy over a larger frequency domain than diffusers that were just placed on the floor.
The results from the chamber qualification work will help improve chamber design and sound diffusivity quantification. In addition, the data on mounting techniques will lead to advances in the understanding of how to properly mount these diffusers in an experimental setting.