Spaced mics sound warm and ambient because incoherent signals exceed loudspeaker angle.

Evidence

For tonal signals, such as harmonic complexes, the virtual sources may be localized inconsistently; the localization varies with frequency, and a virtual source may be perceived to be wide. However, sound recorded with spaced microphone techniques is often considered to be more ‘ambient’, ‘airy’, or ‘warm’ than sound recorded with coincident microphone techniques (Lipshitz, 1986). A reason for the more pronounced room response in AB techniques than in XY techniques is the omnidirectional response, which does not attenuate the diffuse field. Another effect that emphasizes the room response is that, due to the considerable distance between the microphones, the captured signals are incoherent within a 1-ms window for most directions of arrival. When such incoherent signals are applied to loudspeakers, the interaural cues of the listener suggest directions exceeding the directions between the loudspeakers in the stereophonic set-up, which may lead to higher detectability of the reverberant sound (Pulkki, 2002). — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1846

Categorization

• DEEPTHINKING: Explains a beloved warmth/ambience via a concrete perceptual mechanism: incoherence pushing interaural cues outside the loudspeaker arc, which is a genuinely non-obvious causal chain.
• XREF: The warmth claim (Lipshitz 1986) connects to earlier chapters on interaural cues and diffuse-field perception in this same book.