The Vandersteen 2Wq sub has a crossover system that is designed to make the transition from main speakers to sub at 80 Hz. The crossover that is inserted between the preamp and power amp rolls off the frequencies below 80 Hz that are going to the power amp, while the subwoofer's interal amp has a boost curve that is the inverse of the crossover rolloff. The result is flat frequency response. Because Vandersteen designs the 2Wq this way (but NOT the V2W, which gets it signal from the LFE output on a surround processor), it is necessary to have main speakers that are fairly flat into the upper part of the first octave (20-40 Hz). If the main speakers are not fairly flat down to the upper 30-Hz range, then there will be a dip in frequency response in the range where the 2Wq and main speakers overlap.
Richard Vandersteen is quite direct about the desirability of having a stereo pair of 2Wq subs (less necessary with a V2W, which was designed mainly for home theater LFE). Not only does having a stereo pair of 2Wq's enhance the listening qualities of the system, but it also provides an additional 3-6 db of gain when compared to a single sub (thereby giving the pair of 2Wq's roughly the same output as a single V2W). I know from my own experience with the 2Wq that having a stereo pair makes a SIGNIFICANT improvement over a solo sub.
Richard Vandersteen is quite direct about the desirability of having a stereo pair of 2Wq subs (less necessary with a V2W, which was designed mainly for home theater LFE). Not only does having a stereo pair of 2Wq's enhance the listening qualities of the system, but it also provides an additional 3-6 db of gain when compared to a single sub (thereby giving the pair of 2Wq's roughly the same output as a single V2W). I know from my own experience with the 2Wq that having a stereo pair makes a SIGNIFICANT improvement over a solo sub.