Both. The port allows for less restriction, so the sub moves more. The tuning of the port allows for specific frequencies to pass easier, thus being "accentuated" (for lack of a better term) and therefore sound louder.
THanks for the imput, so now my next question is... i have a bmw so getting bass into cabin is difficult. so i wanted to do a ported enclosuree sealed to back seat and was wondering if it would be better to put port through the ski pass or to have 2 smaller subs or 1 larger with port elsewhere in trunk?