Conventional and intensity-based sound transmission loss measurements have frequently been compared in the literature. Looking at published results determined under laboratory conditions, one would come to the conclusion that it is only possible to obtain good agreement between the two methods in a very restricted frequency range. It has often been reported that the intensity method gives lower values of the sound reduction index than the conventional method at low frequencies and higher at high frequencies.
The purpose of this paper is to demonstrate with experimental data that excellent agreement between the two methods can be obtained in a fairly wide frequency range (80 Hz-6.3 kHz), provided that the measurements are carried out under optimum conditions. As pointed out by several authors, the only reason for systematic deviations between the two methods is the effect of having a partition that is highly absorbing in the receiving room.
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