Bottoming out is simply the overexcusion of a sub, causing the voice coil former to hit the back plate of the motor. It can happen in any box, but is most common in ported boxes when the sub is playing too far below tuning and acts as though it isn't in a box at all, causing it to overexcurt easily. Tune low enough and you really don't have to worry about it.does the ported box have anything to do with the bottoming out of the subs????? Ive always been pretty biased towards ported boxes....