ok i have 2 12" w3 subs in a truck box that i built and it sounds horrible. it sounds like the subs are bottoming out and i know that these subs are great because everybody told me that jl is one of the top brands so i baught a new box computer designed do u think that will do the trick on makeing them sound good?
If thats a sealed rectangular box at 49"x16"x8.5" then with 3/4" mdf it comes out to a lil less thn 1.4 ft^3 a sub which should be fine.
If its trapezoidal in shape, i.e. one side is longer than the other(8 and 5 inches) each sub would get a lil less than 1.05 ft^3 which is pretty close to the minimum and would probably sound a lot "boomier".
If its a ported enclosure then thats a whole other ball of wax, but if its sealed you could try adding polyfill(Walmart pillow stuffing). It might cut down on upper bass "ring". Use about one lb per sub and see if there's any improvement.
I don't know about the bottoming out deal, however. Are these new subs? and what are you powering them with. Do you know how much airspace(or dimensions) this "new box computer designed" has?
Unless you built a really poor box it might not provide much of an improvement.
Oops, I forgot to account for driver displacement. Those airspace figures would actually be around 1.33 ft^3 and .98 ft^3 each in a common enclosure. If you have the subs isolated with a 3/4" divider it would be slightly less(1.3 ft^3 and .96 ft^3).