Fiberglass &Mdf box questions.

[Bigrick31]

ok so in maybe a week or so (whenever i have some time off of work) i am going to start building my new box. the box is going to be for 2 xxx 12s its going to be a ported box. first question how much airspace is too much for 2 xxx 12s because i may be able to pull off 6^3ft before displacement.
second question. ok my box is going to be built down into my spare tire well. so how then do i figure out how to tune the port? the formula calls for a height but on a curve there are an infanite number of heights so how do figure out the tuning in this case.

on my box i am going to do a pluged for for daily and comps. so last question what fq works best with 2 xxx in comps or daily?

[ShakinSupra]

Go by internal volume of the box. You'll need to calculate the internal volume of your spare tire enclosure, you can do this with displacement. Make a box of a certain volume, fill it with something (Water is the most accurate for displacement), and see how many times you can pour it into your spare tire enclosure. You should be able to get pretty close with this method.