Abstract
Absorption coefficients determined by the reverberation chamber method on the same material in different laboratories are not in agreement. The discrepancies were noted with several materials tested in both the NBC and J-M laboratories. An investigation, involving comparative measurements on materials of different absorbing efficiencies, was undertaken to determine the reasons for the variations. The results indicate that the order of agreement depends on frequency and the absorptivity and size of the sample under test. Various reverberation time formulas have been proposed and of these the Millington formula tends to give the best agreement and most reasonable results under the test conditions. An attempt is made to define the limiting assumptions of the formula empirically from absorption vs. sample area data obtained during the investigation.
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