Hello everyone, I am in the process of designing a 4th order bandpass box for my 2 Sundown Zv3 12s. This build will be mostly for SPL numbers but would still like to be able to play some music with it. I talked to Sundown and they said to use 1 cuft per sub for the sealed portion with a 3:1 ratio. So I have a box design with a sealed portion of 2 cuft and a ported portion of 6 cuft (all after displacement). The subs will be inverted firing into the sealed portion with the motor in the ported portion. The ported side will be 41" w x 20" d x 17" h (outside dimension). My question is about tunning. What should I tune the ported side to? Should I use a large rectangle port or round ports or aero ports? What port area per foot should I use? This is going in the trunk of my 2007 Ford Focus. The car peaks around 48hz. Any and all help will be greatly appriciated. Thanks.