Understanding chair absorption characteristics using the perimeter-to-area method

Measurements of the sound absorption of several blocks of chairs with varied perimeter-to-area (P/A) ratios were used to examine how chair absorption coefficients are related to their physical characteristics. Because the P/A method combines the results of several samples of each type of chair, a more accurate understanding can be obtained of how the physical properties of the chairs are related to their sound absorption characteristics. Unoccupied chairs are shown to have a wide range of characteristics and it is necessary to test each type of chair to accurately predict their effect in an auditorium. However, the absorption characteristics of occupied chairs are strongly influenced by the absorption of the occupants and an approximate average sound absorption characteristic can be useful for predicting the effect of occupied chairs in an auditorium. Although the variations of sound absorption with row spacing are related to P/A, the variations are quite different than when simply changing the P/A for chair samples with constant row spacing. Both chair underpass height and chair back height affect the absorption characteristics of theater chairs, but the effects can be influenced by the presence of carpet under the chairs or by occupants in the chairs. Common sources of increased sound absorption in each octave band are identified and discussed.