Uncertainty aspects regarding the input for reverberation time predictions

Abstract

The outcome of a reverberation time prediction cannot be more accurate than the combined accuracy of input parameters. In the current procedures of measuring absorption coefficients and using them in prediction models at least two aspects regarding the accuracy of absorption coefficients are quite underexposed:(1) The precision of the measurement: the reproducibility both within one laboratory as between different laboratories or laboratory conditions; (2) The accuracy of the measurement: the dependency of the absorption coefficient on the measurement procedure in general. The upcoming ISO 354 improves both aspects by means of a more elaborate qualification procedure, the use of a reference absorber combined with a correction procedure, as well as a guidance for the extrapolation of the results to other dimensions. Still, it is interesting to think about the impact of the remaining accuracy. To what extend is an acoustic consultant “at risk” using absorption coefficients, apart from using correct modeling algorithms. Two different, but common cases, can give an idea of the influence of the accuracy, two situations in which the reverberation time heavily depends on one absorption material: a class room with an absorptive ceiling, and a concert hall with absorptive chairs.