First of all IM BUILDING A WHOLE NEW BOX. Im not using existing sealed boxes. I want to put 4 12" Subs in my car but im going to make 2 different boxes. I was thinking of making each box 4 cu/ft before all the displacement. Tune it to 20 Hz using a 2" Diameter port. In order to get 20hz it would need to b 5.29 inches long. Now how much louder would this box get over a sealed box, all i listen to is rap. BTW thank you So much everyone for all the help. I have had SOOO much trouble with all this ported box stuff thats why i always made sealed but thank you everyone for the help. I also didnt know if u used a smaller diameter port that it would require a less amount of tube to get the hertz as comparded to a larger sized port.