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RE: really? do the math (it's easy!)

The issue is "where does the reverberant field begin".

Picture a low frequency one below the lowest room mode, at these frequencies your room is a leaking pressure vessel and this "containment" of the bass pressure is the only free lunch in audio, "room gain".

Be aware too that a flexing wall or floor etc is also a diaphragmatic absorber and a sink hole at that frequency.

AS soon as you increase the frequency past the first mode, one is in the modal region where a measurement easily identifies large peaks and dips in the response in the room.

The larger the room, the lower the first mode is and the more numerous the modes are as you go higher up. With a large enough, live enough room one can reach the critical distance and the reverberant field at that point no longer has large peaks and dips, the modes are so dense they have averaged out. There is zero voice intelligibility as well as the time information has been completely scattered and all is left is a noise with the same power spectrum as the acoustic power of the source.

That condition is pretty normal in very large spaces and when public address announcements are barely intelligible as a result of the direct sound not being high enough over the "noise" or reverberant sound.

At the dimensions of a living room and typical loudspeakers it is usually the specular reflections close to the loudspeaker which harm imaging the most, and the side walls are often the source.
One way to "see" where absorption will help is to place a mirror on the wall where you can see the tweeter of the closest speaker from your sweet spot and then replace the mirror with a sound absorbing panel, do both sides..
Remember that critical distance and rt-60 are all terms that were originated for and apply in large scale acoustics and do not apply where the modal density is sparse.

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