Okay, i have a ford focus ZX3. i have had a system in their working problem free for a very long time.
my previous system was a bandpass box with two JL 12-inchers in it. the sound was crisp and the subs hit well.
So i decided to make my own custom box, i guess a fake floor type thing. well what happened was i did not make a bottom or back to the box. when the subs play, sometimes i get a really low noise and odd soundign bass, like the waves are hitting off the metal and sounding like crap.
so i decide to put some carpet on the bottom with thin plywood in it (the stock carpet of my car) that helped a little but not much.
the box is about 7 inches tall and about 40 inches long bye 28 inches wide. it has 4, 4-inch diameter port holes in it also. the spare tire is taken out and my sub is mounted to the chassis of the car.
please, any info would help. is it necessary to use a bottom and back to the box? please respond. would it be ok to use a smaller ply wood. like not 3/4" on the bottom-- i dont want it to raise up much higher. is 40 inched by 28 inches by 7 inches tall too much volume for the subs? do i need to cut it down some?