I know that bass below a certain point is supposed to be omni-directional, but I've heard the omnidirectional sub and I've heard systems where there are two subs in stereo configuration.The two sub system beats the omni hands down.
Of course people have shied away from that by limiting bass in theeir MTM's or whatever, and then just using a sub for sounds below 60 hz.
I still think they would do better with a threeway, and using at least two high X-max woofers calibrated to go down to 20hz. 4 would be better, 6 even better. sound volume could go up, but would go down is distortion in the bass range. I hope to do that some time in the future but don't have the funds at the moment to buy 4 more $130 woofers($520) + the cabinets.
Marlboro