"Ethan Winer" ethanw at ethanwiner dot com wrote:

Wouldn't any low frequencies that are not fully absorbed be reflected in
the same timeframe as if the absorption was not there? Or does the
absorption affect phase as well as amplitude?

Yes, any waves that are not absorbed will get through to the rigid
boundary behind and be reflected back. As for phase, I honestly don't
know. I do know that waves passing through absorption are slowed down a
little. So you'd think that would affect the phase. As you add absorption
to a room you actually lower its resonant frequencies a little. This is
why loudspeakers have fiberglass inside them, to make the box seem
acoustically larger than it really is. So, yeah, phase may be affected,
but this is more a theory issue. In practice, just add as much absorption
as you can. It will never be 100 percent in a typical size room no matter
what you do.

My use of the word phase may have been misleading, but I think you more or
less answered the questtion I was trying to ask. I was thinking in terms
of the difference in the time it takes for sound waves to reflect back from
a high ceiling as opposed to a low ceiling. I was refering to phase only
insomuch as it relates to the reflection time, since comb filtering is, as
I understand it, essentially a product of phase differences between the
direct & reflected signals.

Your preference for hard floors & soft ceilings is well documented. What
are your thoughts on using a totally soft wall facing a hard wall if one
must record in a relatively narrow room ( 12')?