Responses are inline:

I am very surprised that you could get it flat to 30 in a room that large,
at an 80 db listening level.

So was I. I was ready to go shopping for a new sub before I figured that I
should test it first. My room is 15 feet x 22 feet with an 18 foot
cathedral ceiling. I guess-timated that the air volume in the room was
3600. It may be closer to 3300 because the apex of the ceiling is not in
the center. There is a tall 3.5 foot x 12 foot opening to another room
which I'm sure doesn't help things.

You will see substantial improvement with a larger sub, on certain
recordings, because 80 db average does not reflect the level of bass that
can be present, on some recordings. The Fletcher-Munson curves demonstrate
the loss in hearing sensitivity at frequency extremes. Thus, heavy bass
can
easily exceed 90 db on some recordings, even if your average listening
level
is 80 db.

It can hit 90 db at 40 Hz easily, not sure about 30 Hz. Also, this is
measured at the listening position, it doesn't fill the entire room. I
don't listen to pipe organs or rap. What other kind of music goes lower
than ~35 Hz (this is a music only system)? Anyone, please comment on this.


Personally, I am of the opinion that corner placement is best for a sub.
In
many or most cases, this results in room anomalies, but that can be
corrected for by subtractive use of an equalizer. By placing the sub in a
location other than a corner, there is loss of efficiency. For every rigid
surface the sub is adjacent to, add 6 dB of output. The floor adds 6, each
wall adds another 6 db, for a total possible improvement of efficiency of
18
dB. Because ALL but the most expensive subs are challenged to move enough
air, this is important.

There is a three foot high divider (counter top) about 2/3's towards the
rear of the room. The sub sits between this and the listening couch.
Perhaps this is helping it load? I think my room is the exception and not
the rule. Corner placement was so boomy that it was unusable.

In my particular, highly satisfactory experiment, I use an AudioControl
Richter Scale III, which is a combination crossover/equalizer, and a 150
watt Yamaha mono amp, driving the famous NHT woofer in a very small sealed
box. In a cheap imitation of the Bag End design, the woofer is driven
below
resonance. The only reason this works in a 1600 cubic foot room is that
the
sub is placed in the corner of a closet. It is flat as low as I have test
tones, which is 20 Hz, and there is no midbass hump.
My suggestion: put the sub in a corner, and pick up a used 31 band eq to
get
rid of the hump. You may be able to get flat to 20.

Thanks for the recommendation. I used to use their stuff back when I still
cared about car audio. Will a half octave equalizer be enough for this
application if I were to put it back into the corner? When I was testing,
my SPL meter was showing around 82 Db at 30 Hz, ~95 Db at 40 Hz, ~92 Db at
50 Hz then back to ~83 Db at 63 Hz.

Thanks!

-Greg