LTD:
Does 1/8 - 1/4 - 1/4 - 1/4 - 1/8 spacing with 4 sources work better than just having 2 sources as 1/4 points 1/4 - 1/2 -1/4 ? Dashes being manifolds.
IE 16 sources in your 2d front wall diagram. 1 manifold in each trough on the 4th order modes graph.
to see how such an arrangement (or any arrangement for that matter) works, just work through each mode picture one at a time.
for your arrangement, first order mode:
the left side and right side 1/8. one is blue, the other is pink, same curve height at both, so they cancel.
the left side and right side 1/4. one is blue, the other is pink, same curve height at both, so they cancel.
the 1/4 in the middle will not excite the first mode because there is neither blue nor pink.
everything either cancels or does not excite the first mode.
second order mode:
the left side and right side 1/8. one is blue, the other is blue also, same curve height at both, so they ADD.
the left side and right side 1/4. both are in neither blue nor pink. no modal excitement from them.
the 1/4 sub in the middle will excite the pink.
so for the second order mode, you have two blue that are at about 70% of full power and one pink that is 100% power, so 2*70 - 140 MINUS the cancellation from the pink 1*100% = 40% net blue mode excitement.
what you will notice is that all symmetrical alignments "balance" all odd-order modes. so with a symmetrical alignment, the modes that matter are the evens. the 4th is further down the priority list than the second. the arrangement at 1/4 distances cancels or does not excite modes 1,2, and 3. it creates some net modal excitement at mode 4, but again, that one tends to be further down the priority list.
the calculations are performed first in the x-axis (width), then in the y-axis (height), then in the z-axis (depth). sine the 1/4 distance spacing is also working in the y-axis, modes 1,2,and 3 get cancelled or not excited there too.
then one has to do something about the depth modes. seating placement, absorption, or even active cancellation are some strategies there.