The Swarm and Debra subs are 'vented enclosure for correct roll-off to compensate for room gain (ports can be plugged with supplied plugs, if desired)'. I've tried my Debra subs both ways and preferred them unplugged.
The Swarm and Debra subs are an excellent example of using science and good acoustic theory to maximize the benefit for the minimum dollar. They have addressed the biggest issue, the room. It can be done with any 4 subs. You should see what some of the crazy home theater guys do, as the Swarm would never have enough deep bass for them (they want 120db @10 hz), things like quad JTR Captivators. Not to plug another forum, but AVSforums in the subwoofer section has some really great information on setup, tuning, and objective reviewing. The home theater guys have done more for good bass than just about anyone.