That what i got when i calculated, but i was wonder after takin out for port. So i did a winisd thing real quick, and if you tune to 30hz youll have a little less than 5 cubes. your port area is 66.25 inch. a good size for port area is 12-16 sq in per cubic foot of volume of the box. 66.25 sq in for 5 cubes is 13.25 sq in of port for ever cubic foot. It does fall in the range for good port area.