A reverberant field only exists once sound has reflected many times.

Evidence

In this situation, the reverberant field does not really exist; instead, the decay of sound in the room is really a series of early reflections to which the concept of reverberant field or reverberation does not really apply. In order to have a reverberant field, there must be much more than six reflections. A suitable number of reflections, in order to have a reverberant field, might be nearer 20, although this is clearly a hard boundary to accurately define. Many studios and control rooms have been treated so that they are very “dead” and so do not support a reverberant field. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1849

Categorization

• DEFINE: Clarifies that ‘reverberation’ and ‘reverberant field’ are not simply any decay — a heavily damped room decays as discrete early reflections instead.
• XREF: Ties to the earlier statistical-acoustics assumption that sound energy visits all surfaces with equal probability.