So i got a type-r 12", and i need a big ported box for it. Where is a program where i can design a box or could one of you design one for me. Im looking for maximum SPL, it is going into a 1994 toyota 4x4 ext cab pickup
first, volume = Length x Depth x Height for a simple retangular box.
Now decide how high and how wide you want it / can be. For example, where I wanted to put my box was only 28" wide, and I wanted it no more than 15" high so I could see out the back window.
Now you need to know how much your sub needs for air space (from the type-r specs)
If you want it ported, add the volume of the port to the volume of the subs' box volume.
Now you know all the variables except depth, so depth = Volume / [height] / [width]
Those are your dimensions internally. Using 3/4" MDF cut the top and bottom pieces 1.5" longer becuase it needs to overlap.
You can vary this however you like. I usually do slot ports btw.