I have owned a pair of these subwoofers, which were $2500 for the pair, for 3+ years now. When I called Hsu Research, I happened to get Dr Hsu and explained what I had which is a 18 by 35 foot room with cathedral ceiling. I have Legacy Whispers for my main speakers which are excellent, but they do NOT have the deep bass for a room of my cubic content. He recommended a pair of these which have worked out great. I kept lowering the crossover point in the electronic crossover furnished(by changing 3 resistor chips inside the crossover) and ended up at 43Hz. Anything above that did not match good with the Legacy Whispers. I am using 3 of the Legacy amps to drive the speakers, 2 of them for the Whispers, and one for the HRSW210 subwoofers. The amps are the high current Stereo amps that are rated for 400/ch into 4 ohms. The literature that came with the Hsu said they were 4 ohms, but I had a preliminary manual that could be wrong. I did try Velodyne before the Hsu, but Velodyne did not have the output level that the Hsu can attain, at least in my room. I have had no problems with the speakers or the crossover, and the speakers get "exercised" with my classical pipe organ music. I love them. Yes, I do have a large electric bill, the room is wired with 4 separate 20 amp circuits as I like music loud.