I just installed my first system, 2 12" treo SSis on a hifonics 1600. Problem is, the box they are in(i didn't build it, got it for free) is sealed and too small and all in all is just a crappy box. It flexes really bad and leaks in some spots. The other day I noticed this weird sound when I turned it up, and my immediate thought was they were bottoming out. I don't think they'd be bottoming out saying that they're rated for 750 RMS a piece and my gain is 3/4 of the way up, plus they're in a small sealed box. So then I thought it might be the dust cap blowing off, but I'm still not sure. Would building a new ported box that is the right size stop this problem? I have one designed, 4 ft^3 @ 29 hz. My dad just informed me that we have some plywood laying around I could use to build a box. I'm not sure what kind of plywood it is, so my question is: Is any plywood okay to use to build a box? I know birch is like the best, but are other plywoods still good?