Close-miked mono reproduction stays clear because the room barely affects the signal

Evidence

However, monophonic sound reproduction is evidently the most used sound reproduction method, since it is used in telephony. When the microphone is at a distance of a few centimetres from the source, the mouth of the person speaking, the acoustics of the recording room do not have much of an effect on the result, and the timbral quality of the reproduction is good. The disadvantage discussed in the previous paragraph is thus valid only when the captured effect of the room is significant, or, in technical terms, the level of the direct sound is comparable to or lower than that of the reverberant field. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1833

Categorization

• DEFINE: Defines when room acoustics matter: only when direct sound level is comparable to or below reverberant field level.