On ported boxes, it depends on the specifications on the port. A certain length width and height of a port will give a certain tuning depending on the box volume. Sealed boxes can be tuned according to some, but not like a ported box.
You might want to head over to the Enclosure / construction section towards the top of the forum index, that's where the pro box makers chill and they'll be helpful //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif
Plus IIRC there's a sticky on it in that forum. Check it out