See what different boxes do to the response of your sub. Make sure you look at the phase shift and lag that each box induces, not just the decibel curve. A big Lag will sound crap with most music, coz the bass-drum will go thump 1/2 a second late. Verrrrrry annoying.
Like was said earlier: Sealed is accurate and tight, but needs big power to go low & loud.
Ported is loud, and can go quite low, but the lower you tune the box, the looser it'll sound.
have a look at what you can come up with for a bandpass box. They can be quite effective if designed and built right.