The biggest hurdle to good in-room bass is the room itself. The biggest thing the room does is impose a significant peak-and-dip pattern on the output of a sub due to how that sub interacts with the room modes. You can change the peak-and-dip pattern by moving the sub or by moving the listener, but you cannot eliminate it.
Dipoles inherently have smoother in-room bass than monopoles because of how they interact with the room's low frequency modes. This presents a challenge when trying to integrate a monopole sub.
A single sub will generate a much more exaggerated peak-and-dip pattern than the pair of dipoles they are trying to blend with. Two subs will be considerably smoother than one, because each will generate a unique peak-and-dip pattern at the listening position and their sum will be smoother than either one alone.
Four subs will be smoother than two, especially if they are arranged asymmetrically. Your ears will add their outputs to a much smoother summation than any one of them alone, and the impact will not be degraded by the arrival time differences because your ear's resolution in the time domain is much coarser than said arrival time differences. In fact, your ears cannot hear the low frequency output of the subwoofer apart from the room's effects, so for all practical purposes the subwoofer(s) and room form a system.
Imho, ime, ymmv, etc.
Duke
dealer/manufacturer
