Nasa box design po mostly, the port tuned from 37hz to 45hz, and you have to made harder inclosure without air leaks except the port to get hard hitting bass, if you want to feel the bass up to the next block, you have to get serious sub woofer, a 18" and a 2000 watts power handling is a good choice, syempre, along with the serious power supply.
For example:
http://a8.sphotos.ak.fbcdn.net/hphot..._5234539_n.jpg