New box design. 1 18" Btl

[yo_mamas_pimp 0]

Hey,

I'm looking to build a new box strictly for street beating. I'm looking to tune it down to 30 hz. It's going in a Mazda 6 so I don't have excessive room to work with... External dimensions of the box will be 40" wide 27" deep and 17" high (double layer on top). Sub will be facing up as well as the port. I was thinking of putting the sub in the middle of the box, closer to the back of the car, and the port closer to the front of the car facing up.

What would be better for music? 3", 4", 5" or 6" port width?

Any ideas guys?