Critical distance is where reverberant sound overtakes the decaying direct sound

Evidence

As one moves away from a source of sound in a space, the level of direct sound reduces but the reverberant sound stays constant. This means that ratio of direct sound to reverberant sound becomes less and so the reverberant sound becomes more dominant. The critical distance, where the reverberant sound dominates, is dependent on both the absorption of the space and the directivity of the source. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2437

Categorization

• DEFINE: Introduces critical distance, the key threshold concept for intelligibility in a room.
• XREF: Formalizes the same reader-track thread as the direct/reverberant distinction in Chapter 6.