I'm currently in the middle of designing a box for a Rockford T1 12. I was going to use the Powerful Enclosure design that Rockford usually posts for their Power line but they seem to have discontinued it. The problem is that their current vented design is only tuned to 40Hz, and I'm looking to hit probably around 30-32Hz. I used the 12Volt port size calc but the port ends up being smaller for some reason, which seems wrong. Am I tripping?