Relationships among various room acoustic indices

For the last 5 years, the authors have been making acoustical surveys of auditoria in the world at every opportunity. In these acoustical measurements, room impulse responses have been measured using a dodecahedral omnidirectional loudspeaker, monaural microphones, and a dummy head system (Neumann KU81i). In order to get accurate impulse responses with high S/N ratio, the sweep-pulse method and synchronous averaging technique were adopted. From the monaural and binaural impulse responses measured in a lot of concert halls and theaters, such acoustic indices as T60 (reverberation time), EDT (early decay time), D50 (definition), C80 (clarity), Ts (center time), and IACC (inter-aural cross correlation) were obtained, and the relationships among them were statistically investigated. As a result, it has been found that such indices as D50, C80, and Ts are highly correlated with each other and the correlations between IACC and other monaural indices are very low. The binaural impulse responses measured through the dummy head were convolved with dry music and speech signals by digital technique, and they are being used as the test signals for subjective experiments using a transaural reproduction system.