Absorption by seating and audience—Whose figures, whose measurement method?

Abstract

Measuring the absorption coefficients of seating and audience is no easy matter because of the difference in size between auditoria and standard test chambers. An optimum test method remains still to be established. Two authors have published papers on this issue recently in the Journal of the Acoustical Society of America. The designer, though, is left confronted by contradicting figures and test proposals. Bradley (1992, 1996) has proposed a technique which involves measuring about five different configurations of seats to establish the absorption of infinite seat areas and absorption by the perimeter. Davies et al. (1994) deal with the perimeter absorption by testing with and without barriers placed over the front and sides of a test block of seating. Neither method is ideal; Bradley’s depends on extrapolation to the smaller ratios of perimeter to area found in real auditoria, while Davies’ method assumes that the barriers do not introduce any new problems of their own. Beranek in his new book (1996) has reanalyzed measured data from full-size concert halls to produce revised absorption figures. This paper seeks to find what common ground there is between the measurement methods and published data. It will draw on results of some tests on model seating in a model test chamber.