Characterization of diffusivity based on spherical array processing

Characterization of diffusivity based on spherical array processing.

Increasing attention has been drawn to the effects of bad acoustic conditions on quality of life and human health, e.g., difficult speech communication in public spaces, teaching and learning efficiency due to classroom noise and acoustics, and criticism on the design of some concert venues.

Reverberation chambers constitute the primary “instrument” for a number of standardized measurements, some of the most important being sound power determination, sound absorption, and sound transmission loss measurements. A central concept in most theories about reverberation room measurements is the “diffuse sound field”. However, it is well known that these standardized measurements give results that vary rather significantly from one chamber to another, which directly affects the prediction of room acoustical parameters and consequently the room acoustical design. It is assumed that the observed variation between chambers is related to the sound field in the reverberation chamber and its “diffusion” or “degree of diffusivity”. As these measurements assume a perfectly diffuse sound field, the degree of diffusivity is suggested to directly relate to the quality of the measurements. 

The purpose of this study is to assess the diffuse field conditions in a reverberant space using a sound field reconstruction method based on spherical microphone array measurements in combination with advanced spatial processing. Spherical microphone arrays are particularly well suited for applications in non-anechoic enclosures, where the sound waves impinge on the array from multiple directions. The proposed methodology allows for reconstruction of the sound field over a three-dimensional domain and consequently examines some of its fundamental properties: spatial distribution of sound pressure levels, particle velocity and sound intensity. Sound intensity flows inside rooms will be visualized and the incident intensity distribution characterized. Ultimately, the aim is to define a proper and reliable measure of the diffuse sound field conditions in a reverberation chamber, with the prospect of improving the accuracy of sound absorption, sound power, and transmission loss measurements. 


Melanie Nolan
DTU Electrical Engineering
7 APRIL 2020