Measuring the Homogeneity and Isotropy of a Sound Field Using Non-Standardized Quantifiers
Jonathan Snyder, Vassar College ’18 and Prof. David T. BradleyA diffuse sound field is one that is both homogeneous and isotropic. In an ideal diffuse field, the sound energy is distributed uniformly and is directionally invariant. Understanding this energy behavior is essential for the acoustical design of sound-sensitive spaces such as auditoriums and concert halls. Currently, the level of diffusivity in a sound field is described by quantifiers defined in measurement standards, including the relative standard deviation of decay rate, as detailed in ASTM C423. This quantifier, however, only characterizes sound field homogeneity. In fact, all currently standardized quantifiers share this lack of isotropy characterization, which prevents a full understanding of a sound field’s level of diffusivity. Isotropy measurement techniques have recently been developed to address this issue; however, the standardized quantifier definitions have not been revised to reflect this state- of-the-art. The goal of the current project is to explore quantifiers that have not been enshrined in any current measurement standards. Many of these non-standardized quantifiers have been proposed theoretically, tested through computational simulations, or experimentally tested in a limited capacity. However, this previous work has not produced sufficient evidence to justify revising the currently accepted set of standardized quantifiers. In the current project, sound field data have been obtained in an acoustic measurement room known as a reverberation chamber. These data have been processed and analyzed using MATLAB in an effort to experimentally determine the effectiveness of these non-standardized quantifiers and to potentially develop new quantifiers that characterize both homogeneity and isotropy. Results and analysis will be presented.