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Discussion Starter · #1 ·
How far away do you typically need to be from an AT screen to no longer see the perforations? I'm planning on installing a 12 foot wide screen with my first row of seats about 10 feet from the screen - would the perforations be visible from that distance?
 

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Discussion Starter · #3 ·
I imagine that the worst case scenario would be similar to seeing the screen door effect on a white or lighter colored background with a 720P projector. I could see the SDE up to about 12 feet away on my 10' foot diaganol screen. Would the visibility of the perforations be just as bad?
 

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I am probably on the smallest end of the range when it comes to an AT screen. At 2x the image height, I do not see the weave (SmX). What you need to consider is pixel size vs perf (hole) size. The larger the screen, the larger the pixels become. Hole size remains the same.


Here is close up of my screen fabric when I am projecting a test pattern onto it. At this close, you can see the weave. The lines in the pattern are 1 display pixel wide (pattern is 1920 x 1080), so you get some idea of scale.


 

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Discussion Starter · #5 ·
Thanks for the heads up Mark. I hadn't heard of anyone complaining about visible perforations before, but I figured I'd better look into it. Why are you saying that pixel size is more important?
 

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I had to really rotate my fabric to rid moire and I could see the green and magenta lines come and go. I had to keep turning until I reached a point with no lines and at my screen size, I have not completely eliminated them and they may be seen on a really bright scene or on high lamp mode.


So if the perfs are 0.5mm on a 1000mm high screen, then the pixels are 0.925mm so some of each pixel gets lost or refracts off the perf - hence moire appears. If you use the same fabric on a larger screen of say 1450mm, the perf sizes become less of a problem as the pixels are now 1.34mm. You have more of each pixel being reflected back. I'm pretty sure the SmX fabric is 0.25mm.


So in the first example, you have 0.5:0.9 or and in the 2nd example, you have 0.5:1.34. You'll have a better result with the larger screen as less of each pixel is lost through the holes.
 

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My screen is just under 1000mm high (960?). I am using SmX (Marketed as Acoustic Vision in Australia). I have seen much larger screens with the same projector and the effects of moire I had to deal with were not as bad simply due to the hole size Vs pixel size ratio.
 

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Discussion Starter · #10 ·
OK, so if I'm reading you correctly, what your saying is that to insure that you dont have any moire issues, use a larger screen wider than 8ft, or use a screen material that has a tighter weave.
 

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Exactly. I think I really pushed the limits here with an 8 foot screen due to the pixel/hole ratio. I am quite room width challenged, so am prety much limited to 8 foot wide. I wish I did have room for a larger screen, I'd go there for sure.
 

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Discussion Starter · #12 ·
I've been considering the issue of screen size to room size, and the conclusion that I've come to is that in a smaller room a relatively smaller screen still seems huge (as long as your maintaing identical field of views), but there is still something to be said for the gravity of a bigger screen in a bigger room. I dont know if its just psychological, but a larger screen just seems to make a stronger impression. For example, I watched the Super Bowl on a friends 50" plasma from 7' away and it was an enjoyable experience, but if we had watched it on my 10' screen from 10 to 12' away, I can only imagine that it would have been better (not really sure how much better it would have really been though).
 

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Yes, if your room allows a large screen then you should use one. In my case, I am width challenged, so have maxed out the room to given me a 36 degree viewing angle for Scope.
 

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It is theoretically possible, but you'd basically need to be projection onto screen (the type you use to keep out bugs), the kind that's mostly open space. With such a screen it's possible you could line up the screen material with the gaps between the pixels and the open area with the pixels and thus the screen would reflect nothing.


But real world AT screens don't have their problem because like a projector produces light over most of it's area (high fill factor) AT screens are also mostly reflective.

Quote:
Originally Posted by CAVX /forum/post/18126532


My screen is just under 1000mm high (960?). I am using SmX (Marketed as Acoustic Vision in Australia). I have seen much larger screens with the same projector and the effects of moire I had to deal with were not as bad simply due to the hole size Vs pixel size ratio.

FWIW, my screen is 110"x46", also SMX material (though it's the original DIY version Ruben sold before he started SMX). I think what Ruben sells now is an even tighter weave. I've never had a moire problem on any of the projectors I've used with it (InFocus IN76, BenQ W5000, Planar 8150).
 

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I don't know about all AT screens - no doubt they very in their liabilities or lack of. But I brought my projector to one forum member's house who had a popular AT screen. I don't remember being able to see the perforations, even at a 9 foot seating distance.

However, when we were testing focus of the projector up close we had to put up a sheet of white paper in front of the screen. Trying to focus on the screen was virtually impossible as all the wholes blurred away, or made it very difficult to see fine details, lines, pixels up close.


Again, I'm not sure how much effect this had at a distance. The forum member felt the AT screen wasn't quite giving him as sharp an image as he could perhaps get. He had a pull down non-AT Da Lite High Power screen and we watched some of the same HD movie images on it (e.g. King Kong) - and the image certainly looked sharper. But that could also have been a function of the extra brightness of the screen as well.
 

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The point being that whilst an AT screen passes sound one way, it passes light the other, so yes a solid screen is going to be better if it 100% reflective and not 95% or what ever the spec is for either a perf or weave.
 

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Quote:
Originally Posted by TSD444 /forum/post/18132608


How are screens that are only about ~5% perforated "acoustically transparent?" It would seem to me that they would need to have more perforations to effectively transmit sound.

As it turns out, we actually need smaller holes to avoid HF losses. A commercial cinema screen is about 20% perf/80% solid and they cause large amounts of HF losses. Combined with large horn loaded HF drivers and the SMPTE 202X-Curve (cinema eq), cinemas have a world wide execptable system in place. In the home, we need smaller holes and why Sterwart released "mirco-perf" (and they still need eq) and why SmX caused a stir with his claims of even smaller hole sizes and no eq required.
 
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