Boomy bass in home theater room

I have a Martin Logan/Adcom home theater system in a 14' square room (concrete floor (no basement) with typical wood stud/drywall construction). I'm using a single, Infinity 12", 300 watt (RMS) subwoofer. The room is treated with 24, 2'x2' (3" thick) acoustic foam in various wall locations. The bass is boomy, especially in the mid-bass region. I can't change the room. When you get done laughing, care to offer some realistic suggesstions?
This is kind of the poster child room for the PARC (Parametric Adaptive Room Compensation). You have a very high Q factor peak, and no amount of room treatment is going to deal with problems in that low frequency range except for one very large and very expensive custom design Helmhotz resonator (we can design it for you if you really decide to go that route).

I think Rives' suggestion is probably an excellent solution.

Can you identify whether the midbass boom is in the region covered by the main speakers, or by the subwoofer? Does it go away when you turn off the sub? If so, then lower the crossover frequency of the sub and/or turn its volume down.

I presume you've experimented with speaker placement. Have you likewise experimented with listener placement? That can make as much of a difference as speaker placement does. Just walk around the room listening to the bass, and see if there's a region where it sounds natural. If so, try to make that your listening area.

I've had good results using speakers with dipolar radiation patterns in square rooms, as dipoles put about 5 dB less energy into the room's bass standing wave modes due to their figure-8 radiation pattern. If you ever do change speakers, you might consider dipoles (like Maggies), and maybe fill in just the very bottom with a conventional sub.

You might try re-orienting the system along the room's diagonal dimension (not exactly on the diagonal, but close to it, so that you're maximally staggering woofer-to-boundary distances). Also, I'd suggest you replace most of the foam with diffusion (I use fake ficus trees). That's an enormous amount of sound absorption material for such a small room, and in small rooms a little goes a long ways. What all that sound absorption is doing is soaking up midrange and high frequency reverberant energy while having no effect on bass reverberant energy, so it's making the room even MORE bass-heavy. It's working against you, I think.

Best of luck!

The Behringer DSP 90 something, for less than $300 as reviewed in Enjoy the Music and other sites will do what you expect for a lot less than the Rives and other such devices. Supposedly, the only drawback is that you need to read the manual pretty carefully to get the most out of it.....OR.....

try to pull the sub out and away from the walls, until the boominess goes away. Sometimes, location is the most fundamental aspect of setting any loudspeaker/subwoofer in a room. Try this and see if you can save yourself some money.
The limited thickness foam treatments that you have may actually be increasing the apparent "bass bloat" that you are experiencing. Due to their non-linear frequency absorption characteristics, which will suck up the highs and upper mids, the bass will tend to stand out even more. As such, you really have to treat the whole room / entire audio spectrum evenly or know exactly what you are doing when using "partial spectrum" sound absorption treatments.

Other than that, your room acoustics will be very hard to work with. As Rives mentions, the room nodes will be very sharp and hard to tame due to the reinforcing measurements. All square rooms will suffer from this. While opening doors and windows in that room might help somewhat, that is obviously not a real solution, especially at this time of year.

Other than the digital equalizer's mentioned above, an old fashioned graphic or parametric might be able to make things far more bearable for a just a few bucks. You can typically find used multi-band EQ's for anywhere from $20 - $50. Since you mentioned that this is primarily for HT use, the sonic degradation that takes place with an EQ would be far out-weighed by the benefits of a more neutral tonal balance. On top of this, you really don't have to read a manual as these "old fashioned" EQ's are nothing more than a fancy tone control that adjusts band by band. A little trial and error with various slider positions and a few bucks might get you a long way towards enjoyable viewing and listening.

I only mention this as many people are "techno-phobes" and digital gear with thick manuals scares the hell out of them. This is not to mention that reasonable results for low dollars spent is always hard to beat. Sean
I just started using the notch filter in my B&K ref. 30 and found this is one the best features going. You want to look at a different pre. pro.

Yep, no way around things (practicality wise, that is), other than radical "EQ'ing", speaker and seating placment changes (still have challenges thereafter), or, yep, massive bass traps/resonators, etc. Your most pracctical is to move speakers/seats, or (from what you're stating), using some Parametric EQ'ing for your system. At the price of your best option is to "EQ" the sub (fix the 40hz spot), and make sure it's not in the 80hz "hole at the 1/4 points of the room. Basically, you need to place the sub in the "middle" of the room to rid the 40hz peak from the sub/room interaction, which might not be practical. Otherwise, place it in the middle of the front wall behind your center speaker to help minimize the 40hz peak(by putting it in the null there!). Also, sitting in the middle of the room, side to side, will lessen that 40hz mode. Still, 80hz will be peaking there, but you can work that somewhat with crossover/rolloff of sub at 80hz, as well as coupling with Logans rolled off at 80hz a bit, if not perfect, but workable. (and you should be rolling the logans off at 80hz!!!!("small" on the pre/pro, yes!). Running em full range has set backs, espeically in that small room, not to mention dynamic range limitations.(Use THX guidelines).
Best bet is still to add some Parametric EQ to at least the sub ideally(but workable otherwise, as well as check level of sub balance vs. system), and get sub out of corner, and into middle of room more!.
You indeed should do bass traps in teh corners to help remove the sting there, and help room sound. Also, you might be doign a bit too much absorbtion. Try pannels on the sides, a few maybe upfront(although Logans don't like absorbtion behind their speakers so much, so beware!). Really, that small rooms needs some more "diffusion"! Particularly since the Logans severely limit off axis reflections greatly, by their phaae canceling dipolar design! I've sold Logans for years.
Basically, your problems can be tamed GREATLY, by moving the sub into the middle distance/dimmension (if not middle of the room more), adjusting levels/crossover, tweaking, speaker and seating placment (moving speakers near 1/4 points would help 80hz peak (how high is ceiling though?), and/or sitting closer to 1/4 point between/from the front/back wall), and fidgiting with set up. OTher than that, EQing should be considered.
For the record, the Rives Parc is the most transparent Parametric Analog device you'll find for doing speakers, but you'll pay a lot to do all of them with your system price range!...otherwise, concentrate on the sub/levels/ have no other options really
Dipole bass helps tremendously - perception seems to be driven by more than just steady state response. Unfortunately, most of the Martin Logans cross to monopole bass drivers by the time they reach 200-300Hz. You can do that down through the second octave using a speaker like the Linkwitz Orion or Audio Artistry Dvorak/Beethoven. You could also build dipole bass units for your martin-logans.

You'll need a box sub-woofer to reach home theater output levels in the last octave; parametric EQ (the Behringer Feedback Destroyer pro is cheap and fine in that frequency range) helps some there.

If you stick with the box bass, you'll need to use a steep cross-over slope to the sub or equalize everything - with an 80Hz 2nd order high-pass behavior my box main speaker bass hadn't rolled off enough for me to get more than 1dB of difference on big 40-80Hz bass peaks just equalizing the sub.
Pick up an old ashly analog parametric.They are very user frienly.This will remove the bass bumps.Digital parametrics are difficult for the beginners.Get yourself a test disc and a ratshack SPL meter.Put the sub where it sounds best and go from there.Good luck!