BFD: Very affordable parametric equalizer. Will be able to help successfully EQ mid bass back into your sub (although if you don't go way below .707, you may not even have a desire to EQ the mid bass...its when you get to below critical Q of .5 that you'd really need to start worrying about mid bass deficiencies)
REW:Program used in conjunction with a mic/spl meter to measure frequency response in your room so you can get an idea of what needs to be EQed or how flat/peaky your frequency response is.
Click below to find out more.
http://www.hometheatershack.com/forums/bfd-rew-forum/
Steve is right about going with larger drivers. The only drawback of going with larger drivers is that they will usually require a slightly larger box than the smaller drivers. These quality larger drivers are just as articulate as their smaller relatives when placed in the right size box. Often people buy 15" subs, don't know anything about Qtc, and throw these drivers into small itty bitty boxes this causing the final Qtc to be above the magical trade-off point of .707 (the tradeoff is between transient response, low frequency efficiency).
My Avalanche 15" sealed subwoofer is ~around .55 Qtc. At this point there is no reason to boost the midbass and it crosses over just fine to the rest of my system even up to 80hz without sounding empty in the midbass. It doesn't sound like a car sub in the least
