Because of this, ground-plane measurements took on a slightly different meaning to me for arrays. The ceiling and ground are like reflectors of the line. Jim Griffin and others describe this, and it surely makes sense. The ground reflector isn't a good thing if there is a single woofer at ear level, but it's fine if there is an array of woofers from the floor up.

Do you have any other observations about measurement techniques specific to arrays? They're definitely a different breed than point source speakers.

On a similar topic, one thing I suggest to guys with deep pockets is to use several subs in a room. It does sort of the same thing that vertical arrays do to remove floor notch. Using a few strategically-placed subs balances bass throughout the room. One can use a program like CARA to decide where to place the subs.

Earl Geddes suggests a random placement, with one sub in a corner, one sub above mid level height and one or more subs placed randomly in the room. I agree with him on the idea of using multiple sources to improve the uniformity of bass energy throughout a room, although I prefer trying to keep the subs symmetrical and somewhat close to the mains, if possible. My suggestion is a layout that is more like an oblique array, with a few subs at different points along the horizontal and also at different heights. Most importantly, I suggest checking any proposed placement with CARA rather than depending on randomness to take care of averaging. But whichever way you slice it, the idea is to use a handful of subwoofers to smooth room modes.