Curved DIY screen? - AVS Forum
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post #1 of 16 Old 05-29-2001, 11:51 AM - Thread Starter
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I just got back from seeing Pearl Harbor on a very nice screen (Jordan Commons in Sandy, UT). I was amazed how bright the screen was. Maybe I've been looking at my G1000 blown up to 135" for too long, and had become accustomed to fairly dim pictures. Maybe they just replaced the bulb. But compared to most theaters this screen seemed particularly bright and contrasty. I also noticed it was a curved screen, I'm assuming this helps focus the light into the audience.

I'm just about to start construction on my DIY fixed & hinged screen (hinged because I have a "smaller" 61" TV behind it). Has anybody attempted a curved DIY? Would I have anything to gain by doing so? If so, how much should I curve it? Any construction ideas on how to pull such a thing off?

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Jeremy

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post #2 of 16 Old 05-29-2001, 01:04 PM
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Jeremy.

Yes, curved screens are brighter. They can also improve contrast and overall image uniformity.

Do a search for "curved" here (when the search engine is working) and there should be several threads with many ideas for DIY curved screens.

The curved shape will introduce geometric distortion that you might find unacceptable using a digital projector. Before you get too far, you might want to put a sheet of plywood or something in front of the projector first, then bend it and see what a checkerboard or grid pattern does using your G11.

Good luck,
Mike
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post #3 of 16 Old 05-29-2001, 01:05 PM
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Hey Jeremy. It's nice to see someone else thinking along similar lines. (and from the same place too!)

I saw Pearl Harbor at the Wynnsong on a horizontally curved screen, and loved it also.

I don't know if it will help, but I posted a thread wondering some similar things just last week. Here's the link:
http://www.avsforum.com/ubb/Forum9/HTML/001029.html

I'm going to follow this closely and would love to see what you're able to come up with as far as curving a screen. I'm thinking of either doing one myself (this is still about a year away) or buying one from Stewart.

If you'd like, I'd like the chance to meet you sometime.

Matt (also from Provo)

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post #4 of 16 Old 05-29-2001, 01:10 PM
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I built a 161" 16x9 curved silver painted screen.
The main reason I went with the curved screen is to have uniform brightness with a high gain suface. If you are using a low gain screen I do not think there is much to be gained from it.

One other thing I did with the curved screen was take advantage of of the curved surface and reflected the center channel off of it back towards the viewers which gave the effect of the sound coming from the screen.

Deron

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post #5 of 16 Old 05-29-2001, 01:14 PM
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deronmoped

Would you expand a little on the silver paint please? What kind of paint did you use? How did you apply it? What kind of projector are you using?

Thanks,
Mike
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post #6 of 16 Old 05-29-2001, 03:32 PM - Thread Starter
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Quote:
Originally posted by deronmoped:
I built a 161" 16x9 curved silver painted screen.
If you are using a low gain screen I do not think there is much to be gained from it.
My DIY is going to be painted grey. Similar to greyhawk. Very low gain (possibly negative gain)

So a curved screen doesn't increase the overall brightness, it just makes it more uniform? I assumed it would focus more of the light toward the audience. But maybe that doesn't really make sense.

Jeremy

PS Since I can't ever seem to access the search engine anymore, does anybody have any techniques for DIY 4 way masking?

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post #7 of 16 Old 05-29-2001, 03:41 PM
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I'm using a Sony 1272 crt projector.

As for the paint I used a oil based silver paint (Rustoleum brand) I compared it to other silvers and chrome paints and they all looked about the same. I picked a brand I had good sucess with in other uses.

As for the application, that gets pretty hard to get a uniform finish. I tried brushing, rolling and sparying but they left an uneven finish. What I came up with, that gave me a excellent finish is a 86" wide brush. I took some foam and stapled it to a board put a couple handles on it and had the worlds biggest paint brush.

I'm real happy with the end results ( the projected image is bright and uniform ) and after comparing it to some screen samples I think the gain is about 2.5.

I also want to put this out there. I do not think curved screens give you any extra gain they just help concentrate or focus the added light from a high gain screen back towards the user and to use a low gain curved screen would seem to want to wash it self out as the light reflected off one part of the screen would hit the other surfaces being the low gain surface is not directional in reflecting the light back at you.

Deron

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post #8 of 16 Old 05-30-2001, 08:16 PM
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Deron is absolutely right, curving a low gain screen will not help brightness or uniformity. When you curve a high gain screen what you are essentially doing is trying to make the entire screen as bright as the hotspot in the middle, the curve does this by focusing the light towards the viewer (as Deron correctly pointed out). On a low gain screen there is no hotspot and the edges and corners of the screen are already the same brightness as the center, so a curved screen doesn't provide any advantage.

Regards,

Kam Fung
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post #9 of 16 Old 05-30-2001, 10:29 PM
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So why isnt some keen CRT person telling us how good his 9to13 gain curved silver DIY screen is!
Kam,
I am trying something like this-come and see it.
http://www.avsforum.com/ubb/smile.gif

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post #10 of 16 Old 05-30-2001, 11:10 PM
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Rem is there really a 9 to 13 gain screen, or for that mater anything over 4 gain screen out there?

If you do the math on a 13 gain 100" screen using a 1292 projector you would end up with 100 lumens per square foot( 4 times a bright as a TV). You would have to ware a welding helmet and use sun screen. I think all the claims of high gain from a curved screen is untrue.

I have been experimenting with getting a material with a gain of over 3. Silver paint give me about 2.5 do you have any ideas?

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post #11 of 16 Old 05-31-2001, 09:34 PM
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Deron,

I believe Vutec's vertically curved screen is quoted as ~12 gain... Actually, 100 ft. lamberts would not seem 4x as bright to your eyes. We actually perceive light logarithmically, so 100 ft. lamberts would appear approx. 60% brighter than 25 ft. lamberts (if my math is correct). Obviously there are some *serious* trade-offs going on to get that kind of gain...

I would agree with you though, gains above 4.0 are probably problematic to achieve and not really suitable for Home Theatre, even with a curved screen.

If silver paint is giving you 2.5 gain you might try some high quality chrome paints (maybe a spray paint). The better ones give a very reflective finish and might be good for obtaining a higher gain. The higher quality paints generally have a higher metal content to get that "chrome" finish.

Ron, I think I might have to! http://www.avsforum.com/ubb/smile.gif


Regards,

Kam Fung
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post #12 of 16 Old 06-01-2001, 03:21 AM
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hi

how larger the screen could then be if curved, considering the added brightness obtained because of the curve ?
Do we gain 30 or 40% more brightness so we could increase the screen surface by the same % if we go the curved screen route ?
Generally , people go this route for the added cinematic effect and the increased brightness and uniformity.
In France, I saw some curved screens going as large as 150-160" because the owner really wanted to take advantage of the improvements. It was generally with 8" CRTs.

Personally, my plan is to go with a Harkness Hall aluminium tubular curved structure (like in theaters) and a their 1/2 perled microperforated 1.8gain screen for a width of 5meter. It might be overkill http://www.avsforum.com/ubb/smile.gif . The screen costs £450 but the structure goes to £1700. But the cinema effect should be awesome. There's big speakers to put behind too..... http://www.avsforum.com/ubb/smile.gif

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post #13 of 16 Old 06-01-2001, 04:06 PM
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David600,

A curved screen *will not* increase your gain by any amount, it will simply make a high gain screen look brighter. The curve allows you to use higher gains without a hotspot, it will not produce a brighter picture than a flat screen with the same gain (but without the hotspot). Depending on the curvature of the screen and the placement of the seats, you can conceivable use very high gain surfaces (even 3.0 or 4.0 gain "silver" screens).

I don't know if you would be happy with a 5 meter/16 foot wide screen and an 8" CRT (is this your plan? You don't mention what projector you're getting). 1.8 gain is probably not enough to produce a watchable image, especially with micro-perforations. On the other hand, if you have seen other curved screen installations and you're happy with the brightness they produce, then go for it.

Regards,

Kam Fung
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post #14 of 16 Old 06-14-2001, 11:00 PM
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Kam,
David 600 has seen 8in CRT powering 16ft(1.8gain?)think what he(anyone) could do with 4-12gain curved screen(yes both axes(H&V).
I appreciate that you are the "doubting Thomas" in all these avenues so I cant wait till someone shows you.Wish I could at the moment(not ready for prime time but getting closer)but posts like Davids should be swaying you.Lots of people are using/working on curved hi gain screens.Of course this would remove the myth of CRT screen size limitations and this cannot be allowed!http://www.avsforum.com/ubb/smile.gif

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post #15 of 16 Old 06-14-2001, 11:43 PM
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I was wondering about the claims of high gain (upwards of 13) from a curved screen. So after I built my 161" 16x9 with a 18' radius (which is quite a bit of curve) silver screen I started to compare it to samples from screen manufacturers. I did not notice any high gain from my curved screen, the sample it came closest to was a sample from Hurley which was their silver material. I figured I had a gain of 2.5. I belive the curve just concentrates the light back at you, which is different then increaseing the gain of the screen.

I would love to say that my curved screen had a high gain of even 4 or 5, but I just do not see it being any brighter then the high gain screen materials that I compaired it to from different manufactures.

Deron

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post #16 of 16 Old 06-15-2001, 03:41 PM
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For anyone contemplating an extreme (>10) gain screen, be sure to consider the following extreme drawbacks:

1. The viewing cone will be VERY narrow. Move your head from the screen focal point to grab the popcorn and the bright and impressive image turns to complete darkness. Note that there is no way around this - the screen can only reflect the light from the projector. A high gain screen trades a wide viewing cone with low brightness for a narrow viewing cone with high brightness. The higher the gain, the narrower the cone. Gain seems to make some people think there is some magic light increase somewhere but if reflective losses are neglected, the area under the gain vs angle curve has to remain constant.

2. Color shift for CRT's may also become clearly evident in some viewing positions due to the slight offset for the red and blue tubes.

3. For minimal hotspotting, the radius of curvature of the screen has to be very short (unless the screen to viewing position distance is large compared to the screen width). This will make it impossible to get the corners properly focused.

In general a curved, preferably torus, screen is a very good idea in combination with high gain surfaces. However, the concept should not be taken too far and a gain of around 2-3 is probably optimal for most HT-rooms.
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