Background: I have a few (4) NHT SW3S subs. These subs are sealed design, 19"x19"x19", containing single NHT1259 driver. I plan on using them as stereo pairs in front corners of the room. My room measures 3000 cubic feet. All my speakers are NHT, and I like the NHT gloss black look, but from what I have read these subs are flat to only 30hz. So I was thinking about upgrading the drivers, I would like to get flat response to 20hz (or as close as possible). From what I have read on this forum, I realize that [size and type of enclosure + particular driver brand/size + power of sub amp] will yield different performance results, but I want to recycle these sub cabinets, as they are in great shape and I have basically zero building "skills". The sub amp is 4 channels of a Citation 5.1 amp. Questions: * How hard would it be for me to swap out drivers myself? * Is there a 12" driver that would work in this particular sealed 19"^3 cabinet to give me response close to 20hz? * Is my amp sufficient (I think I read that sealed designs require high-powered amps)? * I read a review that said my particular sub is a 3ft^3 box. How? On my HP calc, 19"^3 = 3.97'^3 * Would it be cheaper for me to just sell the NHT subs (as is) and get "new" ones? Thanks for reading. Rich B.