I have small mains. They have frequency response down to 80Hz, but the manual recommends setting the crossover at 100 Hz to 120 Hz. How, then, can one subwoofer driver (even a very high quality one) produce something like 35 Hz while it is also producing 120 Hz? How can it do this without distortion? A friend of mine whose advice I respect very highly says that my future upgrade budget would be better spent on TWO 10" subwoofers (pinnacle ac 100) than ONE DIY tempest 15" sonosub. I agree with him... it would allow one sub to be left and one sub to be right to limit "directional bass" effects above 80Hz (since my mains are so small). The 15" tempest probably doesn't perform well at the higher frequencies I'm looking to fill-in. But can a subwoofer be expected to produce clean, deep bass while also producing 110 Hz?