I am currently in the design phase of building my first sub. A downward firing av12 with an ebs alignment. The port in the design will need to be 24" long with flares on both ends. The port will be on the bottom as well. I am toying with the idea of using either a premade flared port or making my own via pvc and mdf with a roundover. The only place I could find the port with the required length was precision sound products. I haven't called them so I do not know what the price would be. If I make my own, what radius should the round over be? Thanks Rich.