Critical distance is ill-defined in small rooms because short reverberation times fail steady state

Evidence

The situation is very different in the small, more absorptive, rooms used for sound reproduction. Loudspeakers have significant directivity, gradually increasing towards high frequencies. This means that the critical distance would be frequency dependent. In addition, the reverberation times are so short that the concept of a “steady-state” background reverberation is dubious, and that is the basis for the critical distance. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1307

Categorization

• XREF: Connects to the general idea that models validated in large halls break down in small rooms, echoing Toole’s core thesis about domestic listening spaces.