Originally Posted by dragonfyr
And if the separation between drivers is , say 3 feet, the highest they can produce without destructive polar lobing is ~93 Hz.
And that is completely ignoring the impact of the spacing between the drivers and the virtual drivers by virtue of their mirror image equivalence off the boundaries. And as each distance is greater than 3 feet, the corresponding limiting frequency will be still lower.
Think modal distribution and near field polar lobing...
There is a bit more to gain than simply sticking a bunch of spaced drivers up there.
For that frequency range there are any number of alternative topologies that would produce a much greater coherent source as well as greater sensitivity.
Folks would do well to research the origins of the D'Appolito /MTM configuration and discover for just what problem it was designed to compensate... (hint: a 15 degree upward polar tilt when used in conjunction with a passive 3rd order LR crossover...) rather than simply assuming its superior due to its being common...
Any alignment can be picked apart ad infinitum, but I see your point. What about the lobing that happens between a pair of stereo speakers playing a mono source like a bass guitar or vocals (which seem to be usually centered in a mix, along with kick and snare)? No one complains about the horrible lobing there, that varies quite widely with just a few inches of listener position, especially 'phantom center' supporters....
Symmetrical and non-symmetrical alignments have the advantages and drawbacks. Good reading:http://www.birotechnology.com/articles/VSTWLA.html
It goes over exactly what dragonfyr was pointing out, that in the right circumstances, an MTM is a good idea, in others not so much. But once you take into account all of the problems with audio playback (the room and it's multitude of problems, separate sources trying to replicate a 'continuous soundfield', varying listener positions, etc) you have to wonder how much difference one choice will make.
I have picked apart AxiomAudio's center channel speakers with widely spaced tweets, but they get consistent critical acclaim. Would I buy them? No. But going with the above arguments, really only fullrange drivers with uncanny off-axis behaviour would fit the bill, or Danley Synergy Horns. Line arrays? HELL NO. Think of the non-colocated sources, the comb filtering, the defects in their impulse response. Yet line arrays have a good following.
In other hobbies I have enjoyed, there is an adage: "It all works". This is no more true than in surfing, where there are some people who would not ride anything other than a 6'0" thruster, yet some folks can take a closet door and ride a wave with it (or something similar). Here's a vid:http://hydrodynamica.com/totem/lord-board.php
I'm not saying people with a Bose system get the same thing as pnw's Octagon setup, but I have found that the time spent deciding on relatively small choices can detract from enjoyment, unless you are here for the journey, and not the end result.
I've seen people spend more time on the beach switching out fins and debating which one to try than actually surfing....just a thought.
Oh, and I would go with the drawing above, 3 identical vertical WMTMW, especially since 2 of them are already built, making the time from build start to 'fire up the film and get the beer' shorter....