listen to put a sub in bandpass, that box has to be dead accurate.
if you notice, alot of cheaper companies, like dual, and some of the low end subs from brand name companies use bandpass box, because of the low wattage of the subs to produce a louder bass in a bandpass. key is here (lower power louder bass from a cheap azz sub)
for those subs, top of the line apline type x, do a ported box.
they will get loud, and beat down the block.