I'm trying to learn to build ported boxes I used reaudio.com calculator and I've built the box twice at the specs it gives me but the sub doesn't hit low and on the program it shows the port frequency at 30 hz.. The sub Is sa15 d4 v2 but the program doesn't ask for the displacement or sub specs so I found another program it's asking for all the xmax qts and all its asking for the diameter In mm I'm not sure where to find this number or what it means. And qts and port diameter Please help