This article is from the Car Audio FAQ, by Ian D. Bjorhovde (email@example.com) with numerous contributions by others.
This answer is not designed to tell you exactly what kind of enclosure
to build, but rather to give an idea of the advantages and
disadvantages to the simple configurations (Infinite baffle [1st
order], Sealed [2nd order], Ported [4th order] and basic bandpass).
Building and designing more complicated systems (order > 4) is not for
the light at heart.