Optimum methods for the measurement of the absorption coefficients of materials.
For the measurement of the absorption coefficients of materials in a reverberation room, the method currently used by the BBC differs from the ISO-Standard method, in the use of additional diffusion in the room and in the distribution of the sample. For the ISO-Standard method, adequate diffusion is achieved by using additional diffusing elements in the reverberation room, whereas the BBC method relies on the distribution of the sample. In this report, ISO-Standard absorption coefficient measurements are shown to be more appropriate to the design of heavily treated rooms. Absorption coefficient measurements made using the BBC method are more appropriate to the design of sparsely treated rooms. To ensure that measurements at low frequencies in the old reverberation room at Research Department are as reliable as possible, the existing BBC method for the measurement of the absorption coefficients of subdivided samples will continue to be used; additional diffusing elements are not then required. If the sample cannot, or would not usually be subdivided, additional diffusing elements will be installed. The ISO-Standard method for the measurement of the absorption coefficients of materials will be used in the new reverberation room. The use of the ISO-Standard method should reduce the influence of "edge effects" on the measured absorption coefficients.
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