I was thinking about trying 1 RE SE 15 inch sub (600 watts rms) in place of my 2 Infinity kappa perfects (350 each)
Think I'll notice a difference? The 12's were in a sealed box, whereas I was thinking about trying a good tuned TCAB ported box for the se. Same amp for both (infini ref 611a 670 watts rms @ 2ohms)
Infinity has great SQ in my opinion, but that 15 SE would beat those into submission for loudness. You should build a box though, unless TCAB has one that is pretty much the exact requirements.
If I were you I would make (or buy) a ported box for your kappa perfects though. If you have them sealed and are looking for something louder, go ported, it's way cheaper than buying a new sub!
Hm.. yeah, I may try that then. I was thinking that the se may be better in general (sealed or ported) but now I think I'll just trying building my own ported box (which ought to be an adventure). From what I've read building a ported box is quite complicated..