The number one problem in getting good bass in a room is low frequency waves are very long, this creates powerful modes, and lumpy slow muddy bass is the result. The modes move around the room depending on where the bass drivers are located. So the answer is to have bass drivers at lots of different locations. There are still modes and so the bass from any one driver is still lumpy, but by having a lot of them each one is at a much lower level where it causes fewer problems and they all add together resulting in powerful smooth articulate bass.
This being the case is why its better to run the mains full range. They may not have as good low bass as the subs, but to the extent they have any bass output at all it helps average into and smooth out the overall response. Smooth bass is fast bass.
The subs don't have to be spread out. One of the white papers on this mentions four subs basically stacked on on top of the other. Inevitably they cannot all be in exactly the same location, and to the extent they are different each one produces a different set of modes. The effect is maximized by spreading asymmetrically around the room. But its very good even when that isn't done.
This being the case is why its better to run the mains full range. They may not have as good low bass as the subs, but to the extent they have any bass output at all it helps average into and smooth out the overall response. Smooth bass is fast bass.
The subs don't have to be spread out. One of the white papers on this mentions four subs basically stacked on on top of the other. Inevitably they cannot all be in exactly the same location, and to the extent they are different each one produces a different set of modes. The effect is maximized by spreading asymmetrically around the room. But its very good even when that isn't done.