DIY compound curved screen - need help - Page 4 - AVS Forum
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post #91 of 133 Old 01-17-2002, 07:36 PM - Thread Starter
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Correction: "The wire going out the upper left" should read "The wire going out the upper right"
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post #92 of 133 Old 01-18-2002, 05:06 AM
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Don,

Thanks for the pics. Regarding the fan box, you do not have to include 180 degree bends in the air path. A straight duct with the appropriate lining (see my posts above) will do fine if you make it more than 2-3' long. The longer, the better. For this particular design I can see it was convenient, but for the DIY project straight ducts are probably preferable.
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post #93 of 133 Old 01-18-2002, 07:41 PM - Thread Starter
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Guys:

Please help me out.

There seems to be a lot of interest in owning or building a compound curved screen. There seems to be a consensus that a compound curved screen design produces a larger, brighter, better image.

However, it seems, only a few people have them.

I would like to know, what are the barriers to owning this screen? If this is the best, why isn't the compound curved screen more common?

What are the barriers? Are they technical? Are they cost? What would be needed to convince more people to use this screen concept in their home theater?

All input is welcome.
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post #94 of 133 Old 01-28-2002, 12:50 PM
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Hi!

I noticed that this thread slowed down lately, possibly because there is already a lot of good information in it - enough to start sawing away at those boards and tacking up the vinyl. :cool:

As for myself, once I launch this project, I plan on buying Stewart high-gain screen material. Don has generously brought us his know-how and experience in torus screen fabrication to make our home-made toroidal screens less of a hit and miss initiative. It only stands to reason that we all reciprocate and insofar as within our means, purchase our screen material from Stewart. Plus, I wouldn't be surprized if he makes the very best high gain screen material to be found. ;)

Cheers,

Brett
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post #95 of 133 Old 01-28-2002, 01:07 PM
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I typed for 45 minutes last PM, and when my wife was trying to attach pictures she erased the whole thing. When I get the strength again I'll show what I have, but my frame is cut, my material is on order, and my fans come in tomorrow. I've "solved" the limit switch problem, and dealt with CRT range of focus/radius of curve issues as well as what material to order.

By the end of the week, I'll have a LONG update with pics and detailed DIY observations. It looks quite good so far, thanks to all the posters above, especially Don Stewart, who has sort of taken me under his wing on this project.

Thanks,

Jeff

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 #96 of 133 Old 01-28-2002, 07:05 PM
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>>>>Using Guy's string method, the radius you would be working with is double the lens to screen distance.<<<<<

Huh? The radius would be intermediate between the lens to screen and viewer to screen distances, not double. The ends of the string are fixed at the lens and primary viewer head position. Swinging side to side will approximate a horizontal radius, but it will actually be a radius whose rotational axis is the line between the lens and head position. If the lens and head distances to screen are very different the horizontal curvature will vary considerably from an arc. However, that deviation will be exactly what is needed to reflect light back at the primary viewer.

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post #97 of 133 Old 01-28-2002, 08:30 PM - Thread Starter
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Hi Jeff:
It's great to read that your screen is coming out OK. I am still designing my screen.

How did you solve the limit switch problem? At this time I am planning on using a piece of monofilament fishing line. It will be centered left to right and run vertically. The top will be fixed and there will be a small steel weight at the bottom. The weight will only be a few grams. Think of a plumb bob. There will be a proximity switch at the bottom of the screen. It will be adjustable from outside the screen. The switch is a 5mm tubular type. I got the switch as a sample from Balluff.

When the screen moves back, it will touch the line and cause the weight to move back and away from the switch. If anyone feels there could be a problem with this, please let me know.

I am planning on having 2 vacuum settings, a high vacuum and a low vacuum. Both will be adjustable from outside the screen. At low vacuum the screen will deflate but more slowly than just turning off the fans. The high vacuum will be adjusted to be enough to form the proper shape (perhaps a bit higher). The whole assembly will be controlled with solid-state relays. (I also received some samples from a company called WAGO as well as switches and rheostats from Allen Bradley.) I will let you know how it all works.

BTW, I am making the brackets that attach the wooden frame to the wall from 1/8" x 1 1/2" x 8' aluminum angle iron. This is lighter and straighter than wood. Plus, I am having all the aluminum fabricating done to print in a machine shop. The wooden frame will be bolted to the angle iron. This way, I can bolt the wood frame to the wall, mark the curves, remove the frame from the wall, cut the curves and reattach the frame to the wall perfectly aligned.

Also, I am not going to wrap my screen fabric around the frame. I am going to construct a metal wire frame about 3†around the screen. The wire frame will be about an inch behind the front of the wooden frame. The screen fabric will attach to this. I had someone model the concept on a CAD system that had FEM capability. It seems to be a nice way to control (minimize) the fabric distortion that forms at the corners. The wire frame should look interesting but if not I will cover it with a strip of black velvet.

Enough for now. The ideas that this thread have developed are fantastic. I would like to thank everyone that has helped.
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post #98 of 133 Old 01-28-2002, 09:28 PM
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I'm sure we'd all appreciate a complete photo shoot of the entire construction process, especially the ray tracing stage. If you need somone to create and host the webpage for you, send me a PM or email, I'll gladly help out.

As for the vacuum switch, I was discussing it with my friend and we came up with a different solution. What we're going to create is a variable resistance duct (ie. the vent entrace area will be adjustable to make it smaller). That way, we can keep tuning it until it reaches a steady state, providing the correct vacuum for the screen with the vacuum motor running constantly.

You'd could also integrate this with the proximity switch, so that it will adjust the duct automatically until it reaches the steady state. This would seem preferable to having the motor start and stop.

Finally, can someone list what the high-gain screen fabric options for this project are. I've noticed at the www.xtremedtv.com website that they offer a Silver 4.0 gain screen which they say works well with a Torus.
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post #99 of 133 Old 01-29-2002, 05:31 AM
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So this is wht happns when I go away and leave torid screens alone as I was asked to do? I guess it's time to finally make myself one. What greater testament to a man's genius can there be, than when we all follow in his work.

Ken Hotte

"Never forget that only dead fish swim with the stream." -- Malcolm Muggeridge.
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post #100 of 133 Old 01-29-2002, 01:29 PM - Thread Starter
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Guy Kuo:

I am getting ready to make my screen curves using your string method. You seem to be the master concerning geometry here. Therefore, I have a question before I start.

You say to put one end of the string in the middle of the middle CRT. But I was wondering, the CRT face has an area. If the projector could be removed, would it be better to extend the string behind the face of the lens? This way, as the string follows the screen, it also forms a surface in space that would represent the face of the CRT. In other words, if the string is located at a certain point behind the lens, as the string is moved where the screen is, a point on the string would also be where the beam is on the face of the CRT. To me this seems to be the path that an imaginary ray might take.

It’s a minor point but will this method produce more accurate curves?

BTW, I am not trying to criticize your work. I’m just trying to achieve another degree of accuracy. Your idea has made it easier for the DIYer to build an optimized compound curved screen. Thanks.

KBK:
Jump in, we need some ideas here.
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post #101 of 133 Old 01-29-2002, 05:01 PM
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Yes, that would be bit more accurate, but I don't think it would make a great deal of practical difference because the curved screen being constructed has a surface which forms a relatively diffuse focusing of the light.

Guy Kuo
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post #102 of 133 Old 01-29-2002, 06:04 PM - Thread Starter
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Thank you, Guy Kuo
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post #103 of 133 Old 01-31-2002, 08:02 PM
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Stan,

First find out (experiment) how much focus you are willing to lose in the corners...and in how much of the corners/sides. This fact alone will set the tone for how deep your curve can be. The depth of the horizontal curve using Guy's method (which I did) is almost 10" max on a 9' wide screen.

Mike2, who has a torus with a G70 says the out of focus edges/corners are a non-issue. If you accept this, you can go actual depth of Guy's string and Iceman's "sphere". You then can go higher gain (3-4). Mike is happy with his brightness and unphased by the focus issues.

OTOH - Alan has a 2.5 gain Platinum Stewart screen with a 4' deep, 9' wide horizontal only curve. He says he sees hot spotting only on a solid white scene or test pattern...with a movie, it is not visible. He said 6" depth probably would have been perfect. He can focus to the edges.

I took all the above info along with comments from Mike Parker (who tweaked my 9500LC) and CINERAMAX who said that (based on installation experience) that 10" sounded too deep for my PJ and lenses (my lenses are HD10 GT26, which Peter refered to as "simulation lenses"). He said 6-7" sounded more proper for my 9' wide screen. He said the deeper torus screens use "C" or "curved" lenses to achieve focus at full depths ($1300 each!).

BTW, he tried to get me to go wider...and he's a purist. EVERYONE who either owns , builds, or installs them says the benefits far outweigh the disadvantages...I chose to believe them.

I put all the posts and phone calls together and settled on Peter's 6-7" depth. I'm using the same material as Alan. The material itself was chosen by Don Stewart taking into account my theater size and shape, my PJ, and my screen size and depth of curve. He just left a message on my answering machine...it shipped out today!

BUT I RAMBLE...the point of all this was that you have to "temper" the string's measurements fo focus completely. In effect, computer models do the same when calculating for a larger width seating area.

I strongly believe the making of a torus screen is as much art as science, and am listening carefully to those who've actually done them.

My screen should be finished by mid week!

I've been too busy building it to post much, but by the weekend, I'll try to post a thorough progress report, with photos, of everything but the Stewart material. This will follow next week.

I tried to post a LONG report once, but my wife accidently erased it putting in the pics (hey, at least she's letting me do it and taking the pictures).

With my screen size, and input from all of the above, the 2.5 should give me more light than Alan, with no hot spotting.

I'm off the next few days, call me or page me. I have many more answers than questions at this stage. I'm very confident in everything so far. Much of it is easier than you think once you visualize it.

Thanks,

Jeff

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 #104 of 133 Old 02-01-2002, 09:01 AM
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Guys,
I was looking for something else and came across this 40 foot Torus screen in our Image Library.
Regards,
Don
LL
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post #105 of 133 Old 02-01-2002, 09:18 PM
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Thanks Don! You wouldn't happen to have any photos of a Torus screen with the screen material of would you ?
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post #106 of 133 Old 02-07-2002, 04:24 PM
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If you zoom into the RIGHT screen section this is an accuratehttp://www.xtremedtv.com/images/ride...rus%20elev.jpg

Ps. No questions re the Brand depicted.

You have not seen it . OK?
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post #107 of 133 Old 02-07-2002, 06:31 PM
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Why is it that all the commercial torus images I've seen here and on the net look like pretty old images of low quality? It's a product category for the upper end install, but the illustrations we see are repeatedly aged, and recycled ones which aren't exactly inspiring. Where are the new, slick images of torus installs?

Guy Kuo
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post #108 of 133 Old 02-07-2002, 06:53 PM
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Amc is no longer installing TORUS. That leaves the Military applications which are probably classified. bUT THE PICTURE ABOVE DEPICTS THE bestincarnation of all CINEMA TORUS, as the larger ones in Stadium seating cinemas INTERFERE with the acoustics. The one shown above looks and sounds the best of all MOVIE THEATER TORUSses

I did the TORUS webpage to generate interest in the TORUS project for the home before Gerald Nash would pass away. Now that he did, and a great loss to all it was.... I am sure that the TORUS will one day catch up for the home.

The Movie Theater venue as a business is in a state of recession/contraction, without the active marketing of the sigma design group am afraid commercial installations will be limited strictly to simulation. Where the Torus shines.

On the subject of radius as a percentage of throw distance I can quote Gerald Nash :

"the radius is NEVER equal or greater than the throw distance, it is a percentage from 70% to the low 90's."

By the way the picture above is not recycled it is part of a proposal to make a REVOX Projector /spherical simulation hd-10 lens/torus package that would be an officially licensed Home TORUS .

Sorry Sam I led the horse to the water, but you refused to drink, may have to show you how to do good Home Video, again...I am afraid. Maybe.:)

We are feeling out the market locally with 3 prospects. If they bite we will move ahead.

our demo system is a g-90, SNELL & WILCOX/THETA,AND 11 FOOT WIDE torus. WITHOUT CUSTOM LENSES.

Contrary to what has been said a TORUS with a screen radius of 85% TD REQUIRES the special HD=10 lens.

It is amazing to see a well focussed 9 inch projector on such a monster.

Specially if being fed by a Terry.
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post #109 of 133 Old 02-08-2002, 01:59 AM
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Quote:
Originally posted by CINERAMAX

Contrary to what has been said a TORUS with a screen radius of 85% TD REQUIRES the special HD=10 lens.
What special HD10 lens are you referring to?
HD10 -T26 maybe?

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post #110 of 133 Old 02-08-2002, 07:19 AM
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NOPE;

It is a Corning HD-10_? either r for round or s for spherical.

Definetly NOT the gt-26.
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post #111 of 133 Old 02-08-2002, 07:24 AM
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Quote:
Why is it that all the commercial torus images I've seen here and on the net look like pretty old images of low quality?
I find it quite amusing that the screen is obviously tilted the wrong way in the image in question, facing downwards instead of upwards.


Quote:
"the radius is NEVER equal or greater than the throw distance, it is a percentage from 70% to the low 90's."
Is this a squared quote? :D Anyway, I have to take issue with that as it certainly depends on the throw and viewing distances. A CRT setup with a viewing distance of e.g. 2 times screen width will definitely make the optimal radius of curvature quite a lot larger than the throw distance. Actually, a radius equal to the average of TD and VD (don't even think about it ;)) is a very good starting point for an optimized screen and I do not think we have to waste our time with numerical simulations to understand that.
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post #112 of 133 Old 02-08-2002, 07:39 AM
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The iceman is skating on thin ice:)



:)
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post #113 of 133 Old 02-08-2002, 08:25 AM
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Quote:
The iceman is skating on thin ice
?????
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post #114 of 133 Old 02-08-2002, 09:28 AM
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Quote:
Originally posted by CINERAMAX
NOPE;

It is a Corning HD-10_? either r for round or s for spherical.

Definetly NOT the gt-26.
Would a regular HD10 be better than the gt-26, assuming your screen is under 100 inches or so?

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post #115 of 133 Old 02-08-2002, 01:37 PM - Thread Starter
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All this theoretical talk about Torus shapes makes me nervious.
Guy Kuo posted a string method to describe the shape of a Torus screen for each installation. Is this method OK to use or is there a flaw with it?
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post #116 of 133 Old 02-08-2002, 03:13 PM
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I have not analysed any methods described here.

The algorythms used for ray tracing TORUS originally developed by Sigma. were FABRIC GAIN dependent.

I can tell you that one of Gerald Nash's last MAXIMs conveyed to me is that a radius never never never exceeds TD.

With all respect to those that disagree.

The seating area has a big part on this too. If you have a smaller room and will not be installing HD-10 S lenses then you have to make your depth shallower say 7" and your seating area 6 seats wide. I recommend the specially made Stewart 2.8 gain, that Don Stewart supervises the spraying process himself.

I also recommend using the Nash designed circular extrusion for the edges.

Perhaps if Iceman and Guys parabolae was shown here in graphic representation I could comment on it.

Also a torus skin should be purchased with Grommets.

I'll show what a Skin looks like. later.

Those willing to purchase a TORUS 2.8 SKIN, the extrusion, a set of plans, and the proximity sensor should form a group and we will arrange a special production run thru Alan.

This is what a propper TORUS skin looks like. Quit wasting time on alternate methods. This is the best. Some Keystone may be applicable.
http://www.xtremedtv.com/images/torus%20skin.jpg
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post #117 of 133 Old 02-08-2002, 06:11 PM - Thread Starter
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Don't laugh, what is "TD". I any case, I am building a Torus screen.

If such a kit was available a month ago, I would have purchased it. It would have saved me a lot of time. Anyway, I have had fun designing a compound curved screen for my own use.

My frame consists of aluminum angle iron and wood. The aluminum angle iron mounts to the wall studs and the wood frame "box" bolts to the angle iron. This is very simple and accurate.

I have a vacuum system. The motors are inside the screen and the air exhausts at the bottom of the frame. It can not be heard unless your ear is at the in or out of the vacuum box. The vacuum box is removable without disturbing the screen fabric.

I have a method of operating the proximity switch My proximity switch is a 8mm, N.O., DC 3 wire type The switching is 1.8mm. If this is not accurate enough, I have a 5mm switch that switches within 0.68 mm.

At this time I do not want to wrap the screen fabric around the frame. I am thinking of holding it up and slightly back with some brackets around the frame.

When I have all my details worked out, I am going to order my screen fabric from Don Stewart. Don Stewart's screen will cost a little more but as we say in the capital equipment industry, you get what you pay for.

Can anyone recommend a distributor that will give me a good price on the screen material?

Thanks Don for your input. I have learned a lot from the information you supplied to this forum.
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post #118 of 133 Old 02-11-2002, 01:55 AM
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Quote:
All this theoretical talk about Torus shapes makes me nervious.
Guy Kuo posted a string method to describe the shape of a Torus screen for each installation. Is this method OK to use or is there a flaw with it?
There is nothing wrong with Guy's string method. In fact, it is probably as close to perfection as you can practically make it. Still, you have to remember that you will only be optimizing for one position this way.

Perhaps overmuch has been said about optimization. As long as you are reasonably close to the optimal shape, the subjective differences will be very small, if any. As depth of focus will be limiting the optimal radius of curvature anyway, why don't you just find out where the limits will be for your setup and adjust your radius of curvature accordingly?

And for those not too concerned with perfect edge focus, make the radius the average of PJ-screen and viewer-screen distances, or use Guy's string method. The subjective results will be very similar.



Quote:
I can tell you that one of Gerald Nash's last MAXIMs conveyed to me is that a radius never never never exceeds TD.
Completely true IF the optimized viewing position/positions is/are placed relatively close to the screen.
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post #119 of 133 Old 02-11-2002, 08:55 AM
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Stan,

What Ice says has been echoed verbally to me by Don Stewart and Peter/CINERAMAX and Joel of HiRez...all of whom have torus experience.

Don't sweat the details that much.

Mine is DONE! Call Me! Details with pics soon.

Thanks,

Jeff

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 #120 of 133 Old 02-12-2002, 08:07 AM
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Hi Jeff,

Please have your wife post the photos before putting up your added description. We don't want a repeat of your last attempt when your manifesto was lost! :)

I can't wait to see it.

Doug
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