Curved screen...single horizontal vs Torus - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 24 Old 06-27-2001, 08:29 AM - Thread Starter
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How much difference in hot spot elimination, etc will a torus screen make vs. a screen curved in the horizontal axis only? Correct me if I'm wrong, but won't the additional vertical curve of the torus only eliminate problems in the vertical axis...ie. hot spotting that is noted moving your head up and down vs. side to side?

I ask this because of the EXTREME increase in technical difficulty of torus as a DIY project compared to a single curve.



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Currently - Zenith 7" CRT, 80x60 1.3 gain screen

Soon to be - 107x60 1.3 gain...with ?Seleco 250 with Panamorph or "cheap" 9" CRT

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Finally went digital: RS20, ISCO IIIs, DIY 10.5' wide torus screen, Stewart StudioTek 1.3 G3 with 4 way masking and adjustable image size
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post #2 of 24 Old 06-27-2001, 11:49 AM
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Jeff,

You are correct. http://www.avsforum.com/ubb/smile.gif

If you go DIY horizontally curved, you might want to consider a rigid screen. On a tensioned fabric screen the centre may "bow-out," where in the TORUS screen there is a vacuum securing the screen. Anyways, if your curve is not too extreme you should get good results either way.

Good Luck,

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post #3 of 24 Old 06-27-2001, 02:14 PM - Thread Starter
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Wouldnt a screen snapped on behind the concave frame keep its vetrical shape without bowing, or is that still a problem? We have to ask Alan and David how their curved screen in the shop is supported, or is it not fabric?

Do the vacuum screens pull the screen back to a pre-determined hard torus shell, or does the screen material itself have the shape?

I would think it would be hard to pull an elastic material to an exact curve using vacuum...after all we are talking very small tolerances with convergance. Likewise, how in the world would they produce a non-elastic fabric in the exact shape without complex seams?

I have read the forum for years now, has anyone found an industrial material that comes in 5x9' sizes without seams?

I keep hoping people on the screen forum will tell more details about what they do know...Peter, I know you're out there.


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Currently - Zenith 7" CRT, 80x60 1.3 gain screen

Soon to be - 107x60 1.3 gain...with ?Seleco 250 with Panamorph or "cheap" 9" CRT

[This message has been edited by Jeff Smith (edited 06-27-2001).]

Thanks,

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Finally went digital: RS20, ISCO IIIs, DIY 10.5' wide torus screen, Stewart StudioTek 1.3 G3 with 4 way masking and adjustable image size
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post #4 of 24 Old 06-28-2001, 07:45 AM
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Bowing can be a problem depending on the level of curvature.

The vacuum pulls the flexible screen fabric into a perfect curve and a sensor on the inside of the assembly regulates the depth of the curve, you can get a very accurate curvature this way. The screen fabric is not supported except at the sides, the bulk of the screen surface is held in place by air pressure.

You can try searching the screens forum for "TORUS" if you want more information, there have been quite a few threads in the past.

Regards,

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post #5 of 24 Old 06-29-2001, 07:32 PM
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post #6 of 24 Old 07-03-2001, 09:39 PM
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Peter,
Why not(KISS)principle.Use solid board,flexable like melamine,supported by ribs to maintain compound curve.Simple DIY and cheap.Even only approximate in its curve,surely 6+gain is doable.Finesse can come later.Bet Vutec could do a custom proto based on their current designs if they saw a chance to blow by their competitors.Then you would have the free for all that you have pined(longed) for!
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post #7 of 24 Old 07-05-2001, 07:06 AM
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Rew I thought about making a solid compounded curved screen. I still might try it, but working with a single curved high gain screen I found the surface has to be perfect or it's going to show any imperfections and to curve any solid sheet of material in more then one direction is impossible. I have not found any easy way yet but if I do!

Deron

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post #8 of 24 Old 07-05-2001, 02:55 PM
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What about DIY compound screen projects? It should be possible to make something that works. I gave it some thought, and I think I would try to make it from fiber glass. The mould could be a piece of fabric, like eg. a bed sheet or some fabric that is a bit flexible. To keep it into shape I would attach it on top of a "box", and apply air pressure into the box. Then the bed sheet would pop up into shape, and the fiber glass and polyester could be applied. Also some sort of framework to make the construction rigid enough. I don`t think the air pressure have to be high to keep the fabric into shape, maybe a vacuum cleaner would be enough? Anyway, I think this approach could work, but I see a problem in tensioning the bed sheet properly, and accurate enough.

What would be important factors to consider when determining the curvature?


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post #9 of 24 Old 07-05-2001, 03:51 PM
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Ups!
I did a bad job when searching for old threads regarding the Torus, but now I found this.. http://www.avsforum.com/ubb/Forum9/HTML/000621.html

Seems that several people have thought of a fiber glass approach already.

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post #10 of 24 Old 07-05-2001, 09:57 PM
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Deron, Ron,

Yes, curving a solid material in two dimensions is very challenging. The flexible and elastic nature of vinyl screen surfaces make them suitable for compound curvature. Doing the same with a non-elastic surface is problematic to say the least, the greatest difficulty I see is the mating of two sheets because the seam is not straight when the sheets are laid out flat.

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post #11 of 24 Old 07-06-2001, 02:45 PM
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Yes, I believe Mike Parker made a DIY compound curved screen using fibreglass and polyester resin. It's probably one of the more workable ways of doing this. The drawback is surface finish, you can see the fibres on the screen surface. I think Mike might have glued a regular screen to his fibreglass backing, alternatively using a gel-coat may give you a smooth enough surface so that you could paint right onto it.

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post #12 of 24 Old 07-06-2001, 04:37 PM
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Hello Gunnar.

Fiberglass works fine. But there is a fair amount of time and labor involved. You will not see the fibers if you lay it up properlyhttp://www.avsforum.com/ubb/smile.gif

The big problem with fiberglass is properly laminating a high gain screen surface to it. Vacuum bagging would probably work. Don Stewart said they use a custom vacuum laminating cabinet for theirs. For me, it ended up being easier to just start over with a simple vacuum box "torus" screen as suggested by KBK, Peter, and others here last year.

You can then tweak the radii to whatever looks best to you. And, buying material only, it doesn't cost too much to try out different surface gain materials either.

Mike

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post #13 of 24 Old 07-07-2001, 12:56 PM
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Mike2,
Thanks! I`ll probably make a small model to see how the curving work out. I`m not afraid of the labour involved. I plan to use paint to get a high gain surface. Currently I use Draper M2500 material on a custom (flat) frame, but I`m not satisfied with this material. The texture and vertical streaks are visible during bright scenes.

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post #14 of 24 Old 07-07-2001, 05:57 PM
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As I said then, and have since, I have had a sock in it....

That was over six months ago.

Anyway Gunnar, I have a paint that appears to be perfect for rolling, I just have to see what hardness it achieves after full drying.. ie, the surface might be a bit fragile. I'd like some indestructability in the screen, thank you. At least it will always remain fully flexable. Once this rollable/sprayable pre-mixed formula looks right..and it has every chance of being so, it will be put into full production. Then sales begin, and I can start playing around with THAT mix, to get to a high gain mixture for you to try out with on curved screens. Color temp has to be just so, and that's a difficult thing to achieve on the best of days.

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post #15 of 24 Old 07-07-2001, 06:04 PM
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A good high gain paint would make the fiberglass method a lot easier.

KBK. Can you get a good white above 3 without a lot of color shift?

Mike
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post #16 of 24 Old 07-07-2001, 06:56 PM
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Color shift is a function of reflectivity as much as gain is. So, colorshift WILL occur, no matter what. It can only be minimized. A curved screen, SHOULD to a certian extent, alliviate some of the problem. The other half of the equation, is to emply a PJ that has adjustable contrast modulation to account for hotspoting issues, which I believe the more modern designs do. The losses encountered when attempting to handle the hotspotting issue are a concern, but the curved screen makes this much less of an issue with the high gain advantage inherent with the design.

If you are speaking of a high gain paint that inherently does not colorshift in it's own right, (ie, not projector tube proximity sensitivity problems) but overall off center (rehttp://www.avsforum.com/ubb/biggrin.gif6500K) temp, then that may be possible.

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[This message has been edited by KBK (edited 07-07-2001).]

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post #17 of 24 Old 07-08-2001, 03:07 AM
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KBK,
Obviously I have read a lot of posts regarding your paint, and I think it is great if I can buy screen paint ready for application (except maybe some thinning?) I would prefer a paint that can be rolled. I made a screen from a bedsheet, and rolled the bedsheet with regular white, flat latex paint. Worked well, and the slight texture from the roll was almost un noticeable.

Gunnar

[This message has been edited by Gunnar (edited 07-08-2001).]
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post #18 of 24 Old 07-08-2001, 07:20 PM
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Kam,
If I follow you.Home Depot will cut custom sheet of melamine so you wont have any 2sheet seam or blend problems.
It bends in 2 directions with limitations of course but works well with floor mounted CRT.
And the rest as they say "is history."
http://www.avsforum.com/ubb/smile.gifPS How about a Lotus(mint condition)swap for a TORUS(Stewart)

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post #19 of 24 Old 07-08-2001, 10:00 PM
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How do these curved Vutecs differ from the Torus?
Hi-gain model 1250P. Looks like size options are somewhat limited & I do not know the cost.
http://www.vutec.com/ultrahighgain.html

Thanks, Mark

Oops. Upon further review I see that our moderator had posted this same info in another thread. Good job Laurence!



[This message has been edited by damon (edited 07-09-2001).]

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post #20 of 24 Old 07-09-2001, 07:21 PM
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Kam,
Oh good,just what I wanted to hear.Now I wont be leary about showing it to you.http://www.avsforum.com/ubb/smile.gif
Ron

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post #21 of 24 Old 07-09-2001, 09:10 PM
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Ron,

A single sheet of melamine might work, but I'm leary on the strain you would put on the material by bending it in two dimensions.

Regards,

Kam Fung
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post #22 of 24 Old 07-10-2001, 09:02 PM
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I posted previously but it froze-hope this isnt a double.

You caught me out.I didnt frame yet.Thats where you come in(Industrial Design).
As a temporary measure I use swimsuit models to adjust the curvature.Peter's idea.
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post #23 of 24 Old 07-10-2001, 09:09 PM
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Lol http://www.avsforum.com/ubb/smile.gif Look forward to it! How did you make the frame?

Regards,

Kam Fung
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post #24 of 24 Old 07-11-2001, 10:06 AM
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Ron,

It's a difficult problem, I haven't figured out any good solutions to a rigid compound curved screen using flat material. A curve in one dimension, OTOH, is quite easy to do with rigid material.

Regards,

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