I'm building a 4 cu ft box for my friends car and I thought going with a round PVC port would be easier to save me some space since it's going to be hard enough fitting this into the trunk. According to WinISD and the 12volt.com if I have 2in PVC it only needs to be .88 inches long. This seems weird to me, is this accurate and would it sound bad like this? If I go up to 3in PVC it takes just over 3in of length, would this be much better?
A port that small would sound awful. At tuning frequency the port makes almost all the sound, so we need a reasonable sized port. A general rule might be a 3-inch minimum (larger if possible) port for a single 10-inch woofer, a 4-inch minimum (larger if possible) port for a 12-inch woofer. If you look at WinISD it shows port velocity, you want that number to be as LOW as possible.
Okay well I'm using 3inch pvc right now and only about 3.5 inches of port. The box is about 3.7 cu ft and it sounds pretty good. Hits the lows really nice and the higher end stuff it does pretty good as well, but there are 2-3 frequencies that it sounds bad on. I'll check again tomorrow to see which frequencies it was again, but I'm guessing thats because of the lack of needed port area
