There are TubeTraps that absorb down to 25 Hz (those being 2' (.6 m) in diameter. But they start out expensive, and quickly approach insanity. So it pays to only get them as large as needed. Also to be truly effective, they need to go from floor to ceiling in all the corners of the room.

So Dean, you forgot to build the triangle: Small, efficient at low frequencies, inexpensive. Pick two.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris