Objective and subjective assessment of sound diffuseness in musical venues via computer simulations and a scale model

Abstract

This study divides the effects of diffusion on the sound in an auditorium into objective and subjective aspects for assessment and proposes a new subjective assessment indicator, called "diffuseness." First, computer simulations of 12 performance halls having various shapes were carried out to examine the changes in the audience parameters with increasing diffusion coefficients of the walls and ceilings. The results indicate that most of the changes in the acoustic parameters, including the reverberation time (RT) and early decay time (EDT), were less than the just noticeable difference (JND), and there was no obvious tendency. However, when a sidewall diffuser was installed in a 1:10 scale model of a venue, the RT and strength (G) decreased, while the clarity (C-80) increased, owing to the increased sound absorption. The change was larger than that in the simulation and the initial reflection was found to increase. Nine subjective characteristics, including diffuseness, were evaluated for an audible sound source generated based on the binaural impulse response recorded at five points in the auditorium. The results show that despite the small changes in objective indicators, the attached diffuser made a clear and positive contribution to the overall impression as well as the subjective characteristics associated with diffuseness within the venue, such as intimacy and envelopment.