Damp early reflection points, but never cover a whole room in foam

Sound reaches the listener directly and via reflections off walls, ceiling, and desk; strong early reflections comb-filter the response, so damping the main reflection points with absorption helps. But covering an entire room in foam is a recipe for disaster: it hoovers up the top half of the room’s reverberation, produces an unnaturally dead environment unlike real listening rooms, and (because of the cost of covering so much area) forces thin treatment that only removes top end while the bottom and midrange run riot.

Examples

A little acoustic foam at the first side-wall and ceiling reflection points tames comb filtering; blanketing the whole room instead sucks the life out of the highs while leaving low-mid resonance untouched.

Assessment

Explain why damping first reflection points helps but total foam coverage is counterproductive for a mixing room.