I'm trying to tune a large fiberglass box that's about 14 - 15 cubic feet, havent gotten to figure out exactly yet, to about 35Hz. I will be running four 15" RE SE's in it. From the calculator on psp-inc it says I'd need five 6" aero ports at around 17". But I see alot of people on here that say that isn't enough port area. This is for a daily driver that I'd like to sound good and get loud.