I have a 96 reg cab f-15o with a solo baric 15L7 in a 1.6cu.ft. sealed box that sits between the seats how come I lose a large amount of the bass with the doors shut compared to when they are open?

 

You could be encountering a large amount of cancellation. If you can get ahold of a Radio Shack SPL meter you can graph your output buy running some test tones through your system.

Your truck could also be very well sealed. This could result in a perceived 'loss' of bass when the sub has to work against the air pressure in the cab.

Best,
Mark

 

most likely cancellation. try moving your box to different positions in the truck, or changing the direction that the sub is facing, etc.

 

open your windows see if its louder i know my car is way louder with the windows open but im pushing some pretty good air

 

fairly normal to get a 3 or more db jump when you open a door or window, I like to think of it as a port for SPL. You can design so it is as loud with the doors and windows shut but unless you compete in dB Drag there isnt much point.