Basically the compromise is between port length, box volume, and port area. The bigger you make a port (area wise), the longer in length it has to be, and the more internal volume it takes up. BUT... if the port is too small area wise, it's like the sub is trying to breath through a straw. And since the sub is going to move a given volume of air each stoke, the actual velocity of the air being shot out of the port depends on the port area. If the port is big, the air won't obtain as much velocity and will produce nice rich bass. If the port is too small, the said volume of air will be forced at a very high rate out of the small port. Now when this happens at many times a second, the air becomes turbulent and makes noise. 90 degree bends, rough edges, etc make port sound worse. You can reduce them by using flared port (aero ports) 45'ing or kerfing edges inside the box and other such things to make sure the air has a laminar flow through the length of the port and at the entrance and exit of the port. Hopefully this helps if I didn't wreck your eyes with my wall of text //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif
