i build like 10 boxes,3 designs i got from re audio and hey sound good,its just been a long time since i build a box,i know the rules are that it has to have at least 12sq of port per cubic feet and depends what size sub u used thats how big the box is going to be, for exmaple a 15" needs at least a 3cube or higher,i just dont remember how to determine how long the port needs to be to tuned it at a certain frequency