Originally Posted by rms8
Yes, better - but not a complete solution. You're setting up to more-or-less have subs in each of the four corners. This is a common way to get close to a smooth in-room response.
Instead of driving only one room mode (the length mode) you're driving all (most) of them, as well as their odd-number opposites (that's a not a real phrase - let me explain). The 1st, 3rd, 5th (and so on) axial modes generate areas of high pressure at walls and a null in the middle of the room (as well as other nulls and peaks). The high pressure peaks near each wall are 180 degrees out of phase. By driving the mode from both ends, you can get good cancellation of those out-of-phase, odd-number modes. This happens, of course, for any axial mode - not just length. This approach still does not address even number modes.
The bigger concern to me is not exciting each mode from the design phase,but having the flexibility to adjust to what you find when you actually start making noise in the space. Small variations in wall construction (like having a door) will change the way the wall reflects sound - in ways and to extents that are not readily predictable. For instance, you might calculate the center of an out-of-phase standing wave, and plan to place a driver there. If the opposite wall introduces a few degrees phase shift to the reflected wave at that frequency, the position of the peak could move several feet - obliterating the desired effect.
If you do stick with installed LF drivers (not movable), invest in DSP that allows for individual phase, delay, and level adjustment (four channels should be sufficient for this arrangement, IMO). Still bass trapping of some kind is likely necessary.