Aside from loss of brightness, any other downsides to acoustically perfed screens? - AVS Forum
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post #1 of 6 Old 07-26-2001, 10:15 AM - Thread Starter
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looking at Da-Lite 2.8 gain screen with 800 ANSI projector - plenty of room for a little light loss but do a also introduce other problems?
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post #2 of 6 Old 07-26-2001, 11:37 AM
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With any of the digital projectors (LCD, DiLA, or DLP) there is the possibility of a moire pattern caused by the mixing of the dot pattern with the pixel pattern. For this reason, perfed screens are commonly reccomended for analog CRT projectors but not digital projectors. There would appear to be people who do not experience this problem and use such screens with digital projectors, but be aware of the potential problem.

Also be aware that perfed screens are somewhat fragile - it is not uncommon to rip the material along a perf line when assembling one of the permanent stretch-over-frame screen types.

Finally, the perfed screens are better than they have ever been, but will never be 100% acousticly transparent. There is some loss of treble frequencies with all such screens - although if you have a multiband frequency equalizer for LF/Ctr/RF, you can tune this out. (Theaters use horn type speakers with "hot" treble to overcome such losses.)

Of course, the clear advantages of perfed screens are they conceal the front speakers and tie the sound to the screen very effectively. However, much additional thought needs to be put into the use of such screens to avoid or minimize the well-known issues.

I was strongly tempted by such screens, but in the end placing the screen all the way against the wall allowed a larger image size. The front and center speakers were placed under the screen, and since I had only one row of seating, I was able to make speaker stands which tilted the three speakers to aim directly at the listener's ears, taking advantage of the fact that directional hearing is 100% in the horizontal plane, you cannot distinguish vertical sound displacement unless the screen-to-speaker seperation gets really large.

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post #3 of 6 Old 07-26-2001, 12:33 PM
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I would add...

Light will pass through the perfs and be reflected from behind the screen back through the perfs and visible to the viewers. Everything behind the screen should be as dark and non-reflective as possible.

Also, they are more expensive.

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post #4 of 6 Old 07-26-2001, 04:41 PM
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I know Stewart includes an equalizer for the centre channel with their microperf screens, probably as part of their THX certification. Both the Da-Lite and the Stewart perforated screens are supposed to be +- 1 Db out until the very high frequencies, that's theoretically undetectable... http://www.avsforum.com/ubb/smile.gif

Moire is not commonly a problem with DLP or D-ILA, the increased size of the screen door on an LCD will sometimes pose a problem though. I haven't heard of anyone having serious moire problems other than Sony 10HT users, it's probably an combination of the higher resolution and a common screen size. A Cygnus IMX de-pixelizing lens should eliminate the problem, and (of course) reduce the visibility of pixelization.

I think if your perf screen rips during installations most reasonable companies will replace it. That should be a rare occurence, the edge of the screen is usually re-inforced so a tear should only result from a flaw in the screen fabric.

What size of screen are you thinking about? 2.8 gain is a bit high if you want to avoid hotspotting.

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Kam Fung
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post #5 of 6 Old 07-28-2001, 08:59 AM
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Depending on your seating position ,the perforations themselves may be visible!

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post #6 of 6 Old 07-30-2001, 03:38 AM
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I installed a Stewart perf'ed screen back in Feb; some comments:

1. I painted the wall behind the screen a flat black to minimize light reflections.

2. My seating is at 11' and 14'. I don't notice the holes until I am about 8' away.

3. While there may be a loss in the audio, I certainly haven't noticed it. I only have my center behind it. Stewart supplies an equalizer; I didn't use it.

4. You have to try really hard to rip it during installation. While I can see how it can happen, if you take your time and use common sense, you will be fine.

5. I have a 2.0 gain screen and use a Dwin hd700 projector; no problem with hotspotting with this combination. The screen is 82" diag, 16:9.

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