Test fit the 4" port too. This is the only part that's different from the Studio One Pi speaker kit. You will need to order two Part #260-411 four inch ports from Parts Express. Port Length: You can cut the port to the desired length with your skil saw. With a 3" length port I find the speakers have a bit of a midbass bloom. They sound best to me with a 4" length, but some might prefer louder midbass, so anywhere between 3" and 4" is ok depending on your taste. The ports are only $1.70 each, so order four and cut a pair of 3" and a pair of 4".