So are you dead set on doing the Type E? The reason I ask is because Type E and ports don't seem to like each other... pretty far from a flat response.

But if you're gonna do it 2 cu ft tuned to 20hz gave a very similar curve to the sealed box but with a nice gain. FYI you'll have a definate hump in your frequency responce from about 40-80hz which will make some music sound unbalanced but hey if you listen to rap that's where most of the bass happens anyway. It just depends on what your after...

BTW that's 2 cu ft after speaker and port displacement. And a 4" diameter port must be 39.23" long to be tuned to 20hz in a 2 cu ft box. So you're port will displace .277 cu ft and your sub will displace .086 so make your internal dimensions for a gross volume of 2.4 cu ft