A 5"x5" port works well, it has the same area as two 4" round ports. Just remember the port intake needs to be one diameter away from any perpendicular cabinet wall.
slot ports are typically used to make longer ports for low port air velocity builds.I'm trying to model a CSS TRIO12 (w/o PR) and 500W amp in 4.2cu/ft (37.5x16x16" lined) and am having airspeed trouble. Tuned to 22Hz with 20Hz HPF. I've read that 25m/s is the highest acceptable. I plan on front firing the sub and mounting the amp on the back.
I don't have a preference of port vs slot, but I do not know how to make a slot. Creating a square 5x5x26" port in WinISD shows acceptable airspeed (72ft/s). Can a square port be as simple as cutting two 5" wide pieces to length and mounting along the back corner?
Is there a better way to get the airspeed even lower?