AVS Forum Club Gold
Join Date: Jul 1999
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---Lifted from an post somewhere else on the forum ... couldn't find it. ;(
The quality (both audio and video) of the various AT screens available can be easily determined with objective measurements. Certainly, any vendor is going to pick a spec or two which would improve their product's marketing over a competitor. (I like Toyota's recent market campaign ... if everyone is comparing their car to a Camry, why not just buy the Camry.)
The more difficult is the AT vs non-AT discussion (and often the unfounded or entrenched POV's in some quarters). On the one hand it's "AT screws with my VQ" and on the other "AT screws with my audio quality". Great glittering generalities designed (IMHO) to instill FUD, rather than deal with the issues. Let's look at some of these (I am not starting a debate, just laying the matter on the table):
But first, I want you all to try this experiment. Insert the BluRay of Winton Marcellis playing in concert. The amps, speakers are OFF. You are watching on a perfect screen, with a perfect projector (or even just a Meridian 810). You must watch the entire performance. Next, replay the entire performance but turn on the sound system and turn off the projector. Which of the two sessions resulted in the greatest satisfaction? Repeat the same experiment with any good action film. It each case, was the experience audio driven or video driven?
-- Audio Quality
Comb filtering. There's just a gob of arm waving here. Can there be comb filtering? Yup. However, there are several components here (just saying "comb filter" is nothing more than a deliberate FUD factor designed only as a scare tactic). We we look to the recent research on comb filtering (Floyd Toole and others), we can find that (1) comb filtering can actually improve spatial qualities; (2) there are very, very few circumstances where it is audible (usually modal or SBIR problems are being heard, not comb filtering); and, (3) the frequencies where comb filtering can occur due to an AT screen, that filtering is not audible nor measureable at seating distances appropriate to the screen.
Other Audio Distortions. While it is free game to suggest something between you and your speakers is going to distroy your sound experience, what is being ignored is the adverse impact of a big piece of solid vinyl on the front wall of your room behind your speakers. Where's the concern about SBIR and early reflections in this case (carefully forgotten, I'd guess). If audio quality is such a primary concern, then how is it the very same individual would tolerate a timbre mismatch between the L/R and center speakers when the center must be a horizontal cabinet, at a different height and not in line of sight of the second (or greater) row of seating? These are truly very audible distortions.
HF Roll Off. In one sense this is sad that it has become an issue. I cannot tell you how many times I've seen someone install the Cinematic processor (to compensate for the HF roll off) and then turn on THX Re-EQ. What does THX Re-EQ do? Roll off the high frequency content to compensate for the acoustic differences between large spaces (mix stages) and small rooms. The real problem here is until you actually measure the room, you really, really don't know if it needs to be restored or not. The near field measurement of your speakers will provide a clue ... oh, you don't do near field measurements? Oops. (By-the-way, Stewart provides three of the cinematic processors if you specify all three speakers will be behind the screen at no additional charge.)
We have a room with three Aerial 20Ts behind the screen. We've had some very anal pros comment on the great audio quality of the space. It helps that the noise criteria (measured by a third party) is 18NC.
In the end, there are a host of bigger fish to fry in order to obtain extreme audio playback quality then what an AT screen might do and that's iqnoring the acoustic benefits an AT screen imparts to the overall result.
-- Video Quality
Light loss. MicroPerf is approximately 10%...woven screens are much greater some are more than double that. To put this in perspective, if a solid screen/projector combination provides 22 ft lamberts, the microperf will provide just under 20 ft lamberts. The human eye cannot perceive a 10% difference in illumination (part of the "green" function of whole house lighting systems...lights when fully on are really dimmed to 90% if your lighting designer has done his/her job properly). SMPTE standard is 16 ft lamberts...today the preference by users is between 18 and 22 ft lamberts. For many, 20 ft lamberts is too bright in a light controlled room (going much beyond that, you'll destroy your ANSI CR).
Distortion artifacts/loss of resolution. No discernable loss. Let's attack this logically assuming 20/20 vision. At 20/20 vision your visual acuity (resolution of your eyes) is 1/20 degree of arc. MicroPerf is designed deliberately such that at distances greater than 8', the perforations will be less than 1/20 degree of arc. Any loss of resolution, as a result of the MicroPerfs, will also fall below 1/20 degree of arc and hence will not be detectable by 20/20 vision. Moiré is no longer an issue and hasn't been for several years. SMPTE reference viewing rooms (AMPAS screening rooms for example) use either CinePerf or MicroPerf screens for judging film and video quality (CinePerf is bigger holes but, the rooms are bigger and seating distances are greater and outside 1/20th degree of arc.) Obviously, we know that SMPTE and AMPAS don't care or know a twit about audio and video quality. Woven screens? Let's just say that they don't provide a flat surface and most manufacturers of woven screens have a problem with coatings.
Dennis Erskine CFI, CFII, MEI
Subject Matter Expert
Certified Home Theater Designer
CEDIA Board of Directors