Investigating sound field diffusion using the polarization of sound intensity

A diffuse sound field is expected to build up inside reverberation chambers where both sound absorption and sound power measurements shall be performed. In fact, an incomplete internal diffusion prevent the effective application of the related procedures. Although the concept of sound diffusion can be expressed theoretically in several ways and formalized by resorting to diverse models of internal sound propagation, there is still a lack of experimental knowledge to evaluate the grade of diffusion in a reliable and widely accepted way. In this work the problem is faced by studying the fluxes of sound intensities, which are employed to depict the internal sound field of a supposedly diffuse room. In particular the oscillating flux gives rise to a spatial polarization which is represented by ellipsoids. They provide a picture of how the local oscillations of sound energy are distributed. Thus it is possible to investigate how the state of diffusion brought about by room design and/or preparation acts on the sound intensity fluxes and in particular on the local polarization of sound intensity. Based on this concept a series of measures was taken inside a reverberation chamber in different diffusion conditions and the related distortion of the ellipsoids was analyzed. The method does not base on any model of sound propagation but potentially can be used to develop an operational definition of sound field diffusion which can then be experimentally evaluated.