I am trying to create the best tuning and port style that will produce deep low bass. I have a Kicker CRV 15" that I bought off flakko (Great guy ). I am planning on creating a box with about 4 cubic feet + what ever size port I am going to need for a low frequency. So my question is what size port am I going to need to produce the lowest frequencies, preferably in the 30's and what type of port, round or slot? Thanks.