I just order a pair of Fi ssd 18s and was wondering how big I should go on the box? i've read a few forums where people have said go on the smaller side for less peakyness or go on the bigger side and they bang hard. What do you guys think?

also here are my dimensions will I be able to clear 18s?

Preferred dimensions: 44w x 26d x 20h

Biggest I'll go: 44w x 34d x 21h the 34 deep leaves me about 7 inches from my hatch door

I haven't done the math yet for what you have but 14.5 cubes works well. I would also shoot for around 200 inches of port.

It won't be a small enclosure.

And I probably wouldn't listened to someone who designs stuff around bang harder whatever that means.