Revision of sound field diffusion indices determined from incidence directivity

Several attempts have been made to quantify the diffuseness of a sound field from various perspectives. In this study, we focus on the two diffusion indices determined from incidence directivity: directional diffusion coefficient and isotropy indicator. We revise their definitions in the light of physical comprehensibility and also introduce a normalization procedure. These revisions bring an explicit relationship between the indices, which provides their consistent interpretation. Moreover, we conduct numerical examinations using an existing incidence directivity analysis and determine the behaviors of the revised indices in a room with different absorption conditions.