I'm looking at all my options for a new box for my BTL. Current box is 4 cubes @33, but i'm looking to go a little bigger and get a little more port area in hopes of gaining a little low end/spl.

I'm thinking of either doing 4.5 cubes or 4.2.
For those with BTL experience, what would you recommend? I only have 1600 watts on tap, so the bigger box shouldnt' be a problem. Looking to gain some efficiency.

Tuning will be 32hz, and i'm using a 7.45" aero . Oh, and it's an old style BTL, double slug.

What I really want to do is a bandpass, but i'm not sure how good it's going to work.