Every room has a low-frequency limit below which modes, not diffusion, govern sound behavior.

Evidence

Because all rooms have modes in their lower frequency ranges, there will always be a frequency below which the modal effects dominate and the room can no longer be treated as diffuse. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2018

Categorization

• DEFINE: Defines the diffuse-field assumption’s lower bound, a core concept for interpreting room sound.
• XREF: Explains why anechoic and small studios sound colored in the bass, tying back to earlier chapters on room modes and reverberation.