Diffusion and Auditorium Acoustics

Abstract

The prominence of diffusion in auditorium acoustics is commonly acknowledged in the literature, but neither objective measure nor subjective description indicates how it should be defined. Since we know the early sound plays an important part in the subjective success of a concert hall, several acoustical parameters for acoustical design such as EDT, tI, C80, G80, LFE, IACCE, etc. were developed in relation to the early reflections. A sound field composed of a few discrete reflections is of course non-diffuse even in a hall with plenty of surface diffusers. These diffusers may be relevant to the late reverberant sound field, which contributes to the acoustical quality of a hall and will be considered as dependent on the degree of diffusion. Compared with RT60, EDT is a better indication of perceived reverberance, and the quality of reverberant sound may not be that significant to the hall acoustics. Although the early studies of spatial impression focused on the importance of reverberant sound, recent investigations reveal that late-arriving sound from the side of the listener is more important for creating a strong sense of listener envelopment (LEV). Hence the question is: “Is diffusion over-emphasized?” After an overview on this subject, the author suggests several issues to be clarified through further investigations.