Energy relations in concert auditoriums. I

Extensive objective acoustic measurements have been made in 15 unoccupied concert halls and two multipurpose halls used for music in Britain. Only monophonic objective measures at midfrequencies are considered here, in particular, the early decay time, the early-to-late sound index, and the total sound level. The measured results have been compared with traditional predicted values. The widest divergence was found in the observation that the total reflected sound level decreases with increasing distance from the source. A revised theory of sound decay in concert spaces is proposed. This assumes that the total sound is composed of a direct sound component and a linearly decaying reflected component which starts when the direct sound arrives. On average, the measured results are found to be well described by the revised theory. However, certain divergences from average behavior are found; these have been associated with various design characteristics such as the diffusivity of the ceiling, wide fan shapes in plan and absorbent in the stage area. The results help place in context the significance of reverberation time and hall size for concert auditoriums.