Thought I upgraded, but.......
 

I had 2 mtx subs in a sealed box in my crx and it sounded GREAT!!!.........My girlfriend wanted it even louder so we went from a 400 to a 600 watt amp and got better mtx subs in a bandpass box.

This was a mistake with the doors shut and the windows down it sounds muffled kinda, but if you open the door it comes alive in a big way and starts thumping deep and hard. Can the bandpass box not breath unless the doors are open or what.

Thanks,

Bandpass boxes just don't work well...IMO........ They are very limited in the frequency range they will play well in. If you want to go loud go with a large ported box!!!

Sealed= clean and punchy
Ported= LOUD and Boomy
Bandpass= CRAP!

Hope this is a little helpful!

quick fix
 

I've encountered this a few times in my car stereo installing days. My solution has always been just reverse the phase of the subs. It almost always cures the problem. This will cause the subs to push air rather then pull air, or vice versa.

fo sho, band passes suck some ***