I meant to add these will be down firing and here's the second pic it didn't upload in the first post. This is the shape of my box and its a sealed enclosure.
That's what I was looking for, how did you calculate it? I had to do it in 3 parts but it's gotta be easier than that. Only difference between mine and yours is my bottom was 12" and my front was 8" (do to sub depth being 7" and needing 1" for the pole vent.It's hard to come up with something with only a single dimension. Here's an example though. If you're off by a few tenths of a cubic foot it's going to have no effect whatsoever.
Yes that box will be a sealed box, I have a small space to work with and a ported box for a w7 is big even for an 8.That must be a sealed box?
Is it a different routine porting a box like that? How would it be done?