I'm doing a Sub for my son as a graduation present for him to take to the dorm next year. I have settled on the Dayton 12" DVC for the driver and the PE 250W plate amp. (I have two of the 15" DVCs in an IB for our home theater.) Unibox shows good results in vented boxes from 85 to 112 liters, but a 4 inch diameter port goes over the maximum recommended air speed and a six inch port gets way to long. A five inch dia. port, 27 inches long gives an F3 of 20 Hz in a 112 liter box with an Fb of 21 Hz. The problem is I can't seem to find a vendor of a 5" flared port (or any 5 inch port for that matter). I also can't seem to find a source for 5" ID PVC pipe. Does anyone know a source for a 5" ID port? Failing that, does anyone know where to find any kind of rigid tubing with a 5" ID suitable for service as a port? If I can't find a round 5" tube, how well would a square port of equal area work? Would the length needed be the same? I could easily make one from 1/4" hardboard. Any other creative thoughts on what else might work here?