J. S. Bradley
Acoust. Lab., Inst. for Res. in Construction, Natl. Res. Council, Ottawa, ON K1A 0R6, Canada
Previous research has shown that the sound absorption of arrays of occupied and unoccupied theater chairs is related to the ratio of perimeter-to-area of a sample of chairs [J. Acoust. Soc. Am. 91, 1514--1524 (1992)]. This work has been extended by using sound absorption measurements of various sized samples of occupied and unoccupied chairs to predict the absorptive effect of audiences in auditoria. In the auditoria, a full range of modern room acoustics quantities were measured both with and without the audience present. This was accomplished using a maximum length sequence signal and fast Hadamard transform technique to obtain impulse responses without significantly disturbing the audience. The influence of the audience was measured in terms of changes to: reverberation times, early decay times, sound levels, early-to-late sound ratios, and lateral energy fractions. The effect of the audience on reverberation times was compared to the changes in the other quantities. The changes in reverberation times and the added absorption due to the audience is predictable from the reverberation time measurements.