I'm closing in on a design for my ported DVC subwoofer and Unibox tells me that if I use a 105L box (net), 4 inch port and tune to 20Hz the port would be 19.5 inches long and the port air speed would be pretty high. If I go with a 4 inch dual-flared port it needs to be 20.5 inches long. The Aeroports and Madisound flared ports are only 16-17" long (I think). So where can I get longer ports? Are there flares that work with PVC pipe for the center length? I could go with a couple of 3 inch non-flared ports. That gives me about 12% more flow than a 4 inch non-flared. Might be enough. Going all the way to 6 inch diameter makes it REALLY long. Tough to fit in a box.