A room mode’s decay time depends on its path length between reflections.

Evidence

This expresses a similar result to Equation 6.17 except for the difference caused by the differing length of the modal structure with respect to the mean free path. If the length of the modal structure is longer than the mean free path, then, assuming similar levels of absorption, the decay time for the mode will be longer than the diffuse field, whereas if the length is smaller, the modal decay will be shorter than the diffuse field. The length between reflections is both a function of the surfaces that support the mode and the type of mode—axial, tangential, or oblique—that occurs. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2005

Categorization

• DEFINE: Fixes the meaning of ‘mean free path’ versus ‘modal structure’ as the load-bearing comparison for decay behavior.