I'm looking at building 2 subwoofers, one will replace the PW-2200 I have the other will supplement my 2-channel system in a separate room.
I'm not so much looking for suggestions at this point, as I've already decided to go the DIY route, but instead, I'd like to understand what limitations my rooms dimensions and shapes might have on the responses. I want to make sure I don't buy more subwoofer than I really need (as if that's possible), or get stuck with not-enough subwoofer (even worse).

I'm guessing Woochifer, Sir Terrence, Geoffcin, etc (the established members) will have some of the info I need but anyone feel free to chime in...I can hold my own when it comes to speakers, but subwoofers are still rather new to me...

Room A) 24' X 20' the TV is placed along the shorter (20 foot) wall. Optimal sub placement is on the front wall, about 9 feet away from listening position, in between TV and left speaker. Currently, my -3 dB is at 24 Hz in this room, -7 dB is at about 21 Hz (I won't talk about the annoying peaks at higher frequencies, a BFD is on the way).

Room B) 12' X 19', the stereo is placed along the short wall, I listen farfield, about 9 feet way from the speakers (which are 2 ft out from the wall), so seat is about 11-12 ft out from front wall. When I had a 2nd subwoofer, I placed it in betweent the two main speakers with good results. The sub was limited to about 23 Hz at -9 dB as I recall...could be wrong though.

Both rooms have 8 ft ceilings. Both are carpeted, furnished, typical rooms.

I have little understanding of room gain/loss effects, particularly below 40 Hz, and just want to make sure I'm not wasting my time aiming for a 20 Hz goal within +/- 3 dB.

Both drivers I have are about 91 dB sensitive at 1 meter. I rarely listen to HT or music where I'd need an in room response above 103 dB...maybe the odd peak, but I'm usually quite a bit lower, 80-86 dB average volume, maybe some peaks taking it above 100 dB. I'm more about quality than quantity I guess, though I love cranking it for some good progressive rock, or classical performances.
I think realistically, a good 500 watts and 250 watts is all I need for each respective room to make things shake, both drivers can handle more than this though. The PW-2200 I have now is more than enough for me at this point, but I'm trading it for a PW-2100 and then selling that PW-2100 as soon as the first sub is built.

Any comments, or can I just ignore my room and dive right in?