Kudos to you for prior art, but which scenario did you favor? Did you implement? Results, pointers, etc, appreciated.
Thanks for a first jab at my problem.
I can see that my presentation has not conveyed my design questions very well.
Please allow some review and more detail.
As we all know, the simplest DBA is one speaker each in the center of the front and back walls.
The walls create acoustic images of these drivers every room-width to each side;
the ceiling and floor image the drivers every room-height above and below; and
this repeats, including all the diagonals, even out to infinity, for perfectly reflective walls, floors and ceilings.
A two-speaker DBA array centered vertically doubles the horizontal density of this simplest DBA,
but leaves the vertical density the same.
The two-speaker DBA array also shifts the driver horizontally by 1/4 of the room width, but the vertical offset is unchanged.
Nils's beautiful quad DBA then doubles the vertical density, too, also shifting the vertical placement by 1/4 room-height.
In all these configurations, the assumption is that the rear wall array is configured identically to the front wall array.
But it's also clear that the number of speakers and their horizontal and vertical "phasing" can be varied.
So, my fundamental inquiry is, "What would happen if the front and rear arrays were not identical?"
For 1a, the proposed arrays are Nils-style quad at one end, and dual ceiling at the other end.
Note that the horizontal alignment is the same at both ends, with two vertical lines of driver images half a room-width apart, 1/4 room-width on either side of each wall image.
The dual ceiling drivers are vertically offset by 1/4 of the room-height relative to the quad array, and every other driver (image) is missing.
Still, can't the sparser array cancel at least some of the back wall reflections? (How much?)
Regarding 1b: I understand that mismatches of the original and reflected wavefronts will result in non-cancellation,
but wouldn't "different but equalized" speakers get you at least most of the way there?
(I'm gonna have furniture, too; is this speaker mismatch more distorting than furniture?)
The images in 1c similarly are aligned horizontally and offset vertically between the end walls, this time in an attempt to minimize the number of drivers.
How well will this work?
(I observe that one way to think about this configuration is to treat the wavefront as moving along the diagonal
rather than parallel to the walls. Is that useful? Btw, I bet this configuration is most susceptible to furniture.)
1d reflects ignorance about IB manifold design.
I realize this may not be the best thread to pose this question.
Sorry, but if someone can point me to...
1e is similar to 1c, but the vertically sparse emitters (and images) are at the same heights
on front and back walls (and images), so does this mean they'll cancel each other better or worse than floor vs. ceiling?
(My guess is 1e is better than 1c.)
The added drivers and their images in my part 2 above are attempting to decrease the maximum separations
between emitters (real and virtual) so that the cutoff frequency could be raised.
Thus, they would be placed in the horizontal center.
2a and 2b enumerate the IB options.
Again, sure, the match won't be perfect, and/or the array will not be fully filled in, but won't there be *some* bandwidth gain?
Which should be better?
In 2c, regarding vertical alignment between the two ends, one suggestion is to place them symmetrically, ie, where one end is slightly above and the other below the horizontal midline;
another suggestion is maintaining the same height from the ceiling/floor.
Or misalign them, and place one end in the exact center where possible.
My guess is symmetry is best, especially for small offsets. But can I get increased bandwidth?
Part 3 seeks advice on how to simultaneously achieve low-frequency reflection and high-frequency absorption.
I suspect the key is that the LF reflections utilize the whole walls, ceiling, and floor, while the HF reflections
can be suppressed by treating their reflections as narrower beams,
but I hope a DBA enthusiast might have already resolved this dilemma.
Thanks to everyone who has taken the time for considering my "out-of-the-box imaginings".
(Seriously evil pun intended.)