Yes, they have sealed enclosures and were designed for use with a sub. The F3 point is about 75hz. Without a sub the deep bass sounds like many of the single driver speakers I have heard - MIA. Here's something to consider: If you bought just the 36 drivers and the crossover parts from Parts Express or Madisound they would cost you about $1,000. A cabinetmaker would charge another $1,500 or more to build the veneered enclosures. So you're getting the whole thing for the cost of the parts. There are several very good reasonably priced subs that can be used with the Linus Arrays. One example would be the Parts Express Titanic 10; the complete kit with driver, 250 watt plate amp, and assembled enclosure sells for $349 (It takes about one hour to assemble). So for $1,350 you could have a high end line array system with separate subwoofer.
Did I mention with the 40 watt Ella tube amp I measured 106-110dB orchestral crescendos at the listening position - just like being there. I hate to sell them but I have too many speakers sitting around gathering dust and I'm working on a couple of new projects, so they have to go.