well i have a alpine type R SWR-1223D and i was looking to build a box heres the spec 2 cubic feet Height 14'' width 20'' Depth 18'' wood thickness 3/4'' what size would i have to have the port?
The specs you have listed above is closer to 2.2 cu ft. But thats OK, slightly larger always performs better. If you just want to use a single 4-inch round port (PVC) then you will need a port around 10-inches long. If you want to follow the example I used in this thread http://www.caraudiotalk.com/audio-forum/showthread.php?t=7031 Then use a port that is 12-1/2-inches long by 1-1/2-inches wide. This port would need to be 16-inches long