Hey George, try this: Cut a 5 3/4" round of a matching or same wood then cut a 5" hole in it. Round over both edges. Cut out the 5" hole in the speaker and trim it out with the ring you made. Does that increase the length of the port by the thickness of the trim ring? Probably yes but perhaps the round over helps. In any case you could use 1/2 or even 1/4" stock for the ring.