I have had a Snell Sub 550 for about ten years, and added a second one a couple of years ago. One thing to keep in mind is that the subwoofer is passive, so you need a separate amp and crossover. The performance is okay. It's a sealed box design, so the bass is pretty tight. They don't shake the room like a Velodyne or newer home theater type sub would, but I find them to work well for music, which is what I use them mainly for. Unless you already have an amp and crossover, you might be better off purchasing a new or used HSU research or Outlaw Audio sub. Good luck.
Mike
Mike