Many, or perhaps most, movie palaces tended to be on the dry
side acoustically.  However, rarely were they acoustically dead.
Echo is something that is never desired in any musical setting.
Reverberation is a different matter.

Reverberation allows the sound to roll out in the room and reflect
off of many different surfaces rather than a parallel surface that
might cause a slap echo.  Fabric of all types acts as a sound absorber:
carpet, seat covers, drapes, stage dressing, etc.  All those columns,
stupids, cupids and other things on theatre walls have a purpose
besides being something to look at -- they break up any potential for
slap echo.  The more plain a theatre room is, the more likely a slap
echo problem may exist.

Curiously, I saw the YouTube offering of the grand opening of the
Loew's Jersey concert.  A tiny microphone is sometimes not a good
window through which to hear things.  That said, I was astounded at
the amount of reverberation within Loew's Jersey Theatre.

For us long-time theatre and theatre organ nuts on the West Coast, we
tend to gage big rooms such as the Jersey against the demolished (in
1963) 4700 seat San Francisco Fox Theatre.  The big Fox was certainly
not live in the sense of a stone cathedral, but the big Fox was far
from a dead acoustic.  When I was in the Jersey a number of years ago,
I was astounded at the "look and sound" of the San Francisco Fox.

In San Francisco also stands Grace Episcopal Cathedral.  It has a
reverberation time of 5-6 seconds.  The Fox was perhaps half of that.
(To get an idea as to the size of the Fox auditorium, you could stand
a 10-story building up from the main floor and not touch the ceiling!)

This could go on and on, but I won't.  Bottom line, echo is not
something you want in an acoustic environment, but solid, equal
reverberation is wonderful.

Tom DeLay
Salinas, California