home made sub box

i built a sub box for a 10" sub that fits between my seats. the sub is outside of the box instead on inside the box, (backwards) but it sounds like straight up shit. both ways, in and out sounded like crap. the box is completely sealed but small. its about 11" wide, 14" tall n about 7" deep... it has some bump but sounds bad and not right...any help would be great...im also running a 500 watt amp.