Originally Posted by Bill Fitzmaurice
You can't eliminate modes. What you want to do is introduce many modes, at different frequencies, each with small effect, rather than just a few, each with large effect.
This is as succinct a description as I've come across, and at odds with the way I've interpreted a lot of what I've read. Or perhaps what I've read wasn't expressed very accurately. Okay, I'll take the blame.
In the Audyssey thread, there is an excerpt from a Toole paper describing the placement of a sub in a null to smooth (?) the response for a particular frequency. I read this to mean "eliminate" but I can see now that the subtlety in my interpretation had greater implications than I understood at the time.
That modes occur in three dimensions should be pretty intuitive even if it's not always stated explicitly. I guess it's enough work to even out the amplitudes of modes front to back and side to side, let alone vertically. Having good bass across a row of theatre seats is probably enough for most enthusiasts. Maybe this.is the source of comments regarding "not raising the sub off the floor." Trying to grok that third dimension in practice may be too headache inducing, or practical, for that matter.
Greddes, using the method he described, indicated decreasing benefit from the addition of the number of sources (subs) beyond three. Three subs, three dimensions. Kind of an elegant way to approach the problem.