Statistical room-acoustics models fail for elongated geometries where surfaces aren’t uniformly visited

Evidence

As α is a number between 0 and 1, this also means that the level of the reverberant field will be greater in a room with a small surface area, compared with a larger room, for a given level of absorption coefficient. However, one must be careful in taking this result to extremes. A long and very thin cylinder will have a large surface area, but Equation 6.6 will not predict the reverberation level correctly because in this case, the sound will not visit all the surfaces with equal probability. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1772

Categorization

• QUESTION: What geometries count as ‘equable’ enough for the diffuse-field assumptions to hold, and what error margin appears before they break down?
• XREF: connects to: Extreme room shapes break reverberation-field formulas because sound visits surfaces unevenly — David Howard, Jamie Angus, coustics and Psychoacoustics, 1811