How absorption and scattering affect reverberation time: studies on a scale model of a classroom

The prediction of reverberation time in rooms with non-uniformly distributed absorption or/and lacking sufficient scattering surfaces can turn out to be a task harder than expected. Seldom these characteristics are found in classrooms, so that their acoustical design may be subject to uncertainties. Unfortunately, though several methods have been proposed, it seems that there is not agreement on a simple, accurate and reliable approach to this task. In this work the problem was tackled by means of 1:16 scale models. Firstly a reverberation chamber was prepared to measure the sound absorption and scattering properties of surfaces. Then typical setups also with uneven distribution of sound absorbing surfaces in a quasi-cubic occupied classroom were reproduced. The effect of scattering was investigated and its impact on the nature of the sound field was quantified. As a result the extension and location of scattering surfaces required in order to make the classical theory effective in the predictions was derived.