There's a lot of calculations that go into tuning the box to a certain frequency with a given volume, so i really suggest getting the chance or finding a friend to download the torres calculator. It's easy, you put in the overall dimensions of the box, then you change the cross-sectional area and length of the port. I'm still working on designing my box and I'm actually getting help from another car audio buddy. From what I hear, it's the best calculator out there so far.