I believe, for bass cabinets you would want a closed back. Since bass tones are made by the speaker cone moving the air, you would want to create more air pressure behind the cone. If you used an open back cab you would lose that kick of bass and end up getting a bass tone with more treble. So, I would go with a closed back with port holes (allows air to escape the box) OR you can do a 3/4 closed back... where you only close in the area directly behind the speakers leaving a portion open toward the bottom of the box. This will give the amp plenty of open space to breath as well as convey the bass tones appropriatly... but I don't build speaker boxes or anything... and I'm only using my engineering background to give an educated explanation of what I would do. Wait for LATS to go more in detail about speaker wiring.