Theory and measurement of early, late and total sound levels in rooms.

A revised theory of sound level distribution in rooms was proposed in 1988, which responded to the observation that reflected sound level decreases as one moves away from the source. This behavior is ubiquitous in concert spaces and has been shown also to occur in an acoustically diffuse space. This paper presents a more general theoretical derivation and compares measured levels of the early, late, and total sound, as well as the early-to-late index, with theoretical predictions. The scatter of measured sound levels in concert spaces about a linear relationship with source-receiver distance was also compared with a theoretical prediction. Two modifications to the basic theory were investigated, though the original formulation proves best for the general concert space. The revised theory matches average behavior well and represents predicted behavior in a diffuse sound field with the same reverberation time and auditorium volume. Consistent deviations within concert halls were matched with design details.