Evaluating the reverberation chamber as a small room: How room dimensions affect the generalization of testing results

Abstract

Testing acoustic properties is performed in specially designed reverberation chambers according to relevant ASTM, ISO, and other international standards. Performing this testing is complicated by the fact that practical considerations limit the size of the reverberation rooms. Where the dimensions of the room are similar in size to the wavelength of the frequency of interest, modal behavior becomes dominant, and the statistical analysis of room acoustics based on the diffuse sound field theory is not sufficient to characterize the sound field. However, standard methods implement formulas which assume a diffuse sound field to compare results from different labs. Using the Maxon Acoustics Lab, a purpose-built floor ceiling test lab comprised of two stacked, 300 m3 reverberation chambers, we will examine the various physical criteria for evaluating a theoretically diffuse sound field. Discussion will include historical debates concerning the validity of comparing measurements in different labs and an analysis of the Maxxon Lab through the lens of various methods for evaluating the acoustic environment in comparison to the statistical analysis for room acoustics. Methods will include analysis of modal density and distribution, sampling of the sound field per ASTM standards E90, E492, and C423, the Schroeder frequency, and other statistical analyses.