I can't speak for Vutec, but with an SR screen, you can place your speaker(s) one inch or one foot away. It does not matter. The white paper on the SR site along with all the independent testing (THX, Mix magazine, Ultimate AV, etc,) bear this out.
I personally have mine almost touching the screen with maybe less then an inch away with my Screen Research screen. Vutec will need to come up with distances that don't affect comb filtering as some perfed screen do.
Comb filtering is a function of frequency wavelength. Since higher frequencies have shorter wavelengths, you typically see the effects in the upper registers of a sweep. Stewart recommends between 10" and 1' and you can see that at about 1k hz the comb-filtering begins (that's upper-midrange through the entire tweeter bandwidth). Since both the Vutec and the SR have "similar" contruction and exhibit little to no comb-filtering through a sweep, you can push the speaker right up to the screen material (the closer the speaker is to the screen, the higher frquency where the comb-filtering starts). The issue with normal perfed screens is that the closer the speaker is to the material, the greater the attenuation to the speaker's output; in effect, the speaker doesn't have the room to "breathe" .
You can determine wavelength with this fomula: 1130/ X hz. 1130= speed of sound in ft/second at sea-level. X= your frequency integer.
Despite what others might say to the contrary of being a purist; it is possible to modify the crossover networks for the speakers to compensate for behind-the-screen-placement.
Here's some examples of speaker manufacturers paying attention to this fact: Snell has a switch on their AMC-2000 that compensates for behind the screen placement, JBL uses DSP processing in all of their SYNTHESIS systems- which can accomodate for said placement, TRIAD can more than likely make the necessary crossover modifications to all of their speakers for behind the screen, and CAT has as a "standard" option a perfed-screen crossover modification available (coupled with their onsite engineering, there's no audible difference afterward).
But these are obviously the exception rather than the rule, and they are rather expensive speakers. In situations where the speakers aren't to this caliber I recommend SR, and in fact have a system in a friend's house where the in-wall speakers (California Audio) are within 2" of the screen when it drops down (a CP2 with black scrim).
So if you're talking about a "fabric style" AT screen, I'd say that you're safe to go within 6" from the screen if you'd like- just remember that the closer to the screen the speaker is, the higher the comb-filtering starts (if there is any). And remember that for the vast majority of adults: our hearing sucks above 15khz (that's a .08" wavelength, give-or-take).
From my experience, these crossover switches being referred to as built into various home theater models are merely tweeter level switches. Not phase compensation switches. Speaker designer can't possibly anticipate all the location possibilites and correct for the complicated phase anomolies that perfed screens create-- especially at all the various distances one might place a speaker away from the screen. The switches mentioned are mroe than likely merely tweeter level switches. Since the crossover is a passive device, the network is designed with a higher tweeter level than normal. The switch is actually adding or subtracting resistors into the high-pass section of the crossover, thus lowering the output (in the flat or off position) or removing them when in the on position. Since most tweeter's are crossed over around 2K and above, (exactly where the comb filtering of perfed screens occurs) shelving up the tweeter can indeed help for the attenuation caused by any sort of material put in front of the tweeter. But correcting for the wild phase anomolies of a perfed screens can only be approached in the time domain with very sophisticated and expensive computer assisted EQ's.
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