Sound power determination in reverberation chambers

The determination of sound power in reverberation chambers is discussed in the light of normal mode theory. It is known that the sound power emission of a source depends on its position in the reverberation chamber and on interference pattern results in the sound field excited. As a consequence, the measured sound pressure varies widely from point to point. It is shown that the sound pressure is proportional to the average contribution of the product of the normal functions at the source and at the receiver. Based on this relation, the determination of sound power emitted by the source at a particular point in the room is devised through the measurements of average sound field as well as by a corner microphone. It is also shown that sound power determined in reverberation chambers by the standard method is always less than the free-field power, and the difference increases as the frequency decreases. This is just what happens in practice, and good agreement with the theory is obtained with earlier experiments. A statistical formula of the sound pressure in a reverberation chamber developed from the exact theory is used to this end.