Adding absorbent-free volume to a hall raises its reverberation time.

Evidence

The first approach, exemplified by the Birmingham Symphony Hall, is to physically add volume to the space via the use of controllable doors or shutters. If the volume added has little or no absorption, the effect of this is to increase the volume of the space without altering the absorption. As we have already seen from equation 6.19, this will have the effect of increasing the reverberation time. In the case of the Birmingham Symphony Hall, the volume of the space can be increased by up to 50% this way. Theoretically this could increase the T60 by the same factor. However, in practice the increase is less than this, due to the absorption in the added volume. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1920

Categorization

• XREF: Instantiates equation 6.19, where T60 scales with volume over absorption — the chapter’s central formula.