I've completed my Tempest SBB4 sub and while I'm quite happy, I want to now create a Sonotube enclosure for size and placement reasons. The SBB4 performs great but it's just so damn big and I can't move it around my HT without making it look like an "eye sore". Anyways, I'm finally getting the hang of LSPCAD except I've forgotten some of my math skills from high school. I was just wondering if someone could tell me the quick formula to figure out what to put in the "Port Min. Area cm^2" field. Please and thanks!!