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Torus and CRT - A Torrific Combo - Part 1 - Page 3  

post #61 of 276
emdawgz1,

Yes a torus is more complex than a simple curved screen. It has 2 curves (1 in the horizontal plane, 1 in the vertical plane) and they are of different radii.

For a quick and dirty run down on design, take a look at garyfritz's post right above yours.

-PGPfan
post #62 of 276
Gary, thanks for explaining, frankly i thought about subpressure when i saw it, but I thought it was too crazy, but obviously it is not... :)

Yes, what kind of fans are they using?
post #63 of 276
Atom used a old Sony 1292Q fan. I will be using an Antec 120mm quiet fan (from a computer). The screen is gently pull into it's curve and held by the vaccum. It is a simple, and elegant solution.

There's a thread in the archives, or archives2, that has the math for a Torus...
post #64 of 276
Just so that you know this works. The radius of the Torus screen I have is a constant radius and the radius is the same horizontally and vertically. It works. Granted that this isn't a true torodial shape but for this application works perfectly.

James, yes once the material takes it's shape you will definately get floppy and wrinkles in it when you turn the fan off.

I use simple 120mm fans. I once tries a quiet fan but found that the quiet fan had to be turned up to a higher voltage than the regular non-quiet type. This negated the quietness of the quiet fan. As I thought about this it occured to me that while a quiet fan may be the same CFM, it must have a lower static pressure (or at least the one I used) thereby requiring more RPM to suck the screen material in properly.

Terry
post #65 of 276
Terry, What measurment did you use to calculate what raduis you should use, viewer to screen or crt to screen or average of the two? or something out of thin air.
post #66 of 276
This is exactly why I plan to use a fabric material and then "harden" it with catalyzed resin. Complex curves are VERY EASY to make with this method. I've done a bunch of custom molded dashboards, and speaker enclosures in this manner and it works very well.

-PGPfan

What type of resin/fabric? Then a spray/roll on surface? I like the idea of not worrying about stretching/ fan / vacume variables. Do tou need to resin both sides?
post #67 of 276
SO you made a spherical screen then?
post #68 of 276
dokworm....is that what it is????
I thought a lot about the string method and changing radius of the curve and decided based on someone elses Torus screen that I had seen that it just wasn't necessary.

Walter.
There were a couple if things I took int account. First that although the distance from the CRT face to the screen should be the radius, it would make the screen much deeper than I wanted. I knew that a larger radius would work based on other screen folks had built. Alan for one. I also know that I wanted the sides of the box to be no more than 12" so that sort of limited my deepest side to 7" or so remember that the vertical depth plus the horizontal depth equals the total depth in the center, which in my case couldn't be more than 12" and more practically 11"). Therefore, I took a string and found where the radius needed to me for that depth....and it worked.

Terry
post #69 of 276
Hi Terry,

Well that sounds simple enough and even better, it worked just fine. So how big is your screen.
post #70 of 276
Quote:
Originally posted by klicklewis
This is exactly why I plan to use a fabric material and then "harden" it with catalyzed resin. Complex curves are VERY EASY to make with this method. I've done a bunch of custom molded dashboards, and speaker enclosures in this manner and it works very well.

-PGPfan

What type of resin/fabric? Then a spray/roll on surface? I like the idea of not worrying about stretching/ fan / vacume variables. Do tou need to resin both sides?
In general, you'd use a woven polyester fabric (like thick 'pantyhose' material) for the basic shape of the torus using the vacuum frame for shape. Saturate the fabric (soak thoroughly) with catalyzed resin. Once hardened, you apply woven fiberglass cloth to the 'backside only' for reinforcement. The front should NOT be glassed. This side will be smoothed and painted for your actual screen.

Hope this helps.

Terry, I'll certainly keep the forum up to date once begun. It's looking about 6 weeks before I'll have time to start, however.

-PGPfan
post #71 of 276
The problem is how do you get an ultra high gain finish with paint?
Are there products out there taht will give you a gain of 3 or more? That would be excellent.
post #72 of 276
Some kind of silver paint ought to do it, shouldn't it?

Ya Terry, if you used the same radius for vert & horiz curves, that's a sphere.

In theory you should use a longer radius for the vert curve. The "ideal" (but not practical) radius for the horiz direction is the average of the screen-to-crt / screen-to-viewer distance. The vert curve is actually a section of an ellipse, with the foci of the ellipse at the crt & viewer. That will produce a flatter curve than a circular/spherical curve based at one of those foci. But I get the impression most people actually make their vert curve MORE dramatic (== shorter radius) than the horiz curve??
post #73 of 276
Quote:
Originally posted by dokworm
The problem is how do you get an ultra high gain finish with paint?
Are there products out there taht will give you a gain of 3 or more? That would be excellent.
Aluminum paint has a super high gain. Tremclad is the brand in Canada, Rustoleum I believe in the States.

I played with it a while ago. Check out the following link for pictures...

http://www.avsforum.com/avs-vb/showt...03#post4550303


James
post #74 of 276
Is gain enough, or does it have to be retroreflective in a coherent manner as well?
They really called a paint Rust-oleum? Would suit my car I guess.
post #75 of 276
Quote:
Originally posted by dokworm
The problem is how do you get an ultra high gain finish with paint?
Are there products out there taht will give you a gain of 3 or more? That would be excellent.
The Rustoleum paint that the guys have mentioned is REALLY high gain. It's what I'm planning on testing first once the 'hard shell' torus;) is done.

I'm really looking forward to playing with it (the torus, not the paint), there is so much potential with a hard shell. One thing I hope to eventually try, there are several companies that make acoustic transducers that can be attached to a hard surface which will then make that surface act as a speaker. Could be interesting on the torus, don't you think?

-PGPfan
post #76 of 276
Yes I guess it would be like taking a slice out of a sphere.

WTS the screen is 106" x 60". Personally I think that the reason for building a spherescreen is that you want to go BIG without compromising contrast.

Terry
post #77 of 276
Terry, thats a pretty good size screen, hell I was thinking of doing one about 78" by about 44" I guess it would be for 16x9. Thats why I'm asking these questions because at 78" wide it just seemed that the center dip would be too great using what seems to be what everyone else is doing. Of course it all seems that my screen will be alot smaller than most. Ah some things I like small, like screens, T, A etc.

Thanks
post #78 of 276
I made a "Torus" screen about two years ago. Nothing special with the construction, but I used the Draper M2500 material. Unfortunately, this was a rather early version of the material with the streaking problem. I could return it to Draper, but the shipping was more than the material..
I`m considering replacing the material, and want to find out if the Vutec Pearlbrite would be a better material? In addition to the streaking problem, the Draper material also has a texture that is visible during pans. I don`t like this, and would like a material that is smooth.

Gunnar
post #79 of 276
Thread Starter 
The PearlBrite is VERY smooth..

Reminds me of a liner in a swimming pool..
post #80 of 276
WTS,
I think that the idea of using a Spherescreen is the idea of going big.....really big.
I generally don't advise folks who are running smaller screens like the one you have to run a Spherescreen. Of course you could make the curves in your side much shallower.

Terry
post #81 of 276
Hi Terry,

In a thread from way back which Iceman started, he has a drawing which is of a 2m wide torus screen. I think I'll try that one, do you konw if the thread I'm talking about.
post #82 of 276
WTS,
Is it the one I referenced on the first page?

Chuchuf,
A couple of people were saying that the G70 was difficult to do with a Torus. I seem to remember you saying that there were only one or two projectors that were difficult to set up with a Torus. Could you elaborate on your experiences with the difficult ones?

Ericglo
post #83 of 276
WTS,
Yes I am familiar with the thread.....good thread. I don't remember his dimensions though. These is also another one that is in the archives showing detailed pictures of the construction of a Torus screen from a few years ago. Very good thread indeed. Alan our host also had a thread on a curved screen he was running at one time that was helpful in that he identified that the curve didn't have to be as deep as the radius from the CRT face.

Ericglo,
Really it was one G70 that I had some challanges on a Spherescreen. I have done 4 total w/ G70's. All 106 x 60.
The problem was that I was running out of Bow and pin adjustment downward on the lower part of the screen. This problem was sort of caused by me in that I tried mounting the G70 a bit higher than it should go for a ceiling mount. I solved most of the problem by lowering the PJ and then used a combination of bow, pin and zone to bring the geometry in.

Terry
post #84 of 276
Terry,
I mentioned this because GScott and Vince_B said they had some issues with the G70 on page 3 of this thread. Maybe we need to come up with a minimum depth at which to build a Torus and still receive its benefits. Of course, this might be projector dependent.

Also, I am a little confused on your dimensions. Earlier in the thread you said you used 3.5" for the vertical and 7" for the horizontal. Now, you say it is a constant radius. Am I misinterpreting the numbers somehow? To add, when you do curved screens for others are they spherical or torii?

Thanks for the input,
Ericglo
P.S. - I guess you are taking the Torus baton from Peter.:D
post #85 of 276
I do not understand it II.

You are using "normal fans". I think that these fans are desinged for the situation when they have free space on both ends. If you will put one side of the fan at closed space, it will not have enough incoming air, it will not feel so much air resistance as it is desinged for and it will spin faster than normal.

Aren not these faster spins dangerous for the fan? Cannot in overheat and burn?
post #86 of 276
Stepan,
Maybe, but I haven't heard of anyone with a Torus burning out a fan after years of use.


Has anyone thought of using Silverstar fabric in a Torus box?

Ericglo
post #87 of 276
So, how would an NEC PG work with a torus screen? (6pg+, no point)

I've looked through a few threads, and I can't figure out specifically how you attach the material to the frame. That is, how do you properly tension it? Do you start out with material taught and staple it in place?

Are these unforgiving with aspect ratio mismatches? Is a 4:3 movie going to look funny on a 16:9 torus?

Exciting stuff! Time to break out the sawz-all! Ha.

Marshall
post #88 of 276
Quote:
Originally posted by Ericglo
Stepan,
Maybe, but I haven't heard of anyone with a Torus burning out a fan after years of use.


Has anyone thought of using Silverstar fabric in a Torus box?

Ericglo
the original SilverStar was rigid. There is a new rollup version, but I doubt it is pliable enough to be used on a Torus. SilverStar's real world gain is about the same as the Vutec PearlBrite which I am sure would be much cheaper.

James
post #89 of 276
Thread Starter 
Quote:
Originally posted by Ericglo

Has anyone thought of using Silverstar fabric in a Torus box?

Ericglo
What an incredible suggestion!

If you had asked this question before, I would have gambled and tried it assuming it is available in a size I need - cost wise it's probably pretty comparable to PearlBrite..

I like everything about the Silverstar other than some hotspotting - but the Torus concept makes it one total hotspot..

Eric, you game to try it?
post #90 of 276
Thread Starter 
Quote:
Originally posted by Semisentient
the original SilverStar was rigid. There is a new rollup version, but I doubt it is pliable enough to be used on a Torus. SilverStar's real world gain is about the same as the Vutec PearlBrite which I am sure would be much cheaper.

James
Guess it would depend if the roll up Silverstar material is bonded together with a backing material to add more rigidity as a pull down..
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