So my friend at work is a building inspector and he knows I want to build a sonosub but I'm having trouble finding a 16 inch sonotube. He grabbed a scrap 20 inch by six feet piece for for me from a jobsite in good condition. I had planned to use a 12 or 15 inch driver but the 20 seems too big. I guess if I put a 12 in it I could have the port on the bottom. Anybody used a 20 inch sonotube before?