Torus Screen Thread - AVS Forum
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post #1 of 10 Old 01-13-2001, 11:19 AM - Thread Starter
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Here's the area that should be reserved for clear and concise (but yet lighthearted) efforts related towards the (hopefully) very interesting discussions on 'toroidially' shaped, (aka 'Torus') screens...

This is aimed towards the discussion of the basic design parameters -for ascertaining a design minima 'center'; so as to get to a realizable, usable AVERAGE screen size grouping of such a screen design.

People are encouraged to add in their desires as to sizing.. but, at the same time, it is quite difficult to come up with a design that suits all. At first, one would think that an average size of some sort would have to be hashed out. That would be the basis of a FIRST ITERATION. SO, please, add your comments and desires as to sizing you would like.. but please be realistic, stick with something that is obtainable and does not stray too deeply into pipe dreams, that fill your personal unrealized desires.

So, in order to get a realistically priced (this is all relative, as such a design -by nature- will have a premium price) Torus screen to come into existence for us all to take a stab at purchasing for our home theaters, this is where we will have to begin.

If the information going into and coming out of this thread is clear enough to be useful, then that screen may very well come into existence....


I personally would like to think that I could get a screen that is largely aimed towards a minimum 1:1.85 ratio, going to a 1:2.35 ratio, all on the same screen (resizing at the projector, of course). The screen would have a width in the 100-110" range. This is hopefully realistic, in light of the light gathering qualities inherent within the specification of such a curved screen. For me, at this time, it would be for CRT use, with 850 lumen or more 8" and 9" PJ's. Such a screen size should be big enough for me if I decide to switch to a higher output Digitally based projector in the future (ugh!). At that point I would pursue re-surfacing of such a screen, with a finish more oriented towards the situations surrounding the usage of digital projectors.

Of course, this intitial post in no way reflects the situation that may and will evolve, it is merely a starting point for discussion.

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post #2 of 10 Old 01-13-2001, 11:57 AM - Thread Starter
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Acoustical noise problems are one of the parameters (within the useage and implementation) that a Torus screen user has to deal with. For instance, a large amount of the noise coming out of the projector(like the light output) is aimed directly back at the seating area. Noise control AT THE PROJECTOR is paramount to reducing such as a problem. Usually, with a flat screen, the noise coming off of the one surface is not a problem (the screen is not noticable amongst all of the other realizable noise off of surfaces). Due to the fact the the CURVED screen gathers the projector noise coming off of the front o the projector, and aims it back at the viewer, (thus, elevating it slightly above the other noise in the room, on average) it SEEMS to be louder than it is. In that exact spot (where your head is) it actually is.

Noise off of the back wall, and from the audience and surround speakers can be a problem as well. I would suspect that noise from the audience, projector and rear surround speakers to be the most relavant noises to be dealt with. Long reverbration times in the room are to be avoided at all costs with this type of screen.

What this means is that attentionto noise control in the room is inherently a given concern. Does that mean more cash on the room than the screen? Not nessessarily, just some common sense - and attention paid. Absorptive materials should be placed in appropriate areas.

A noise absorptive shadow box around the perimeter of the screen would be a big plus as well, for those who wish to go whole hog. This would have a major impact on the intelligibility of speech and the usage of center speakers.

If it turns out that a perforated screen is out of the question (for the screen to be financially feasable) and it probably will be, then a center speaker above and below the screen center should be the obvious solution, with the balance between the two altered so the sonic image appears to be coming out of the center of the screen for all or most viewers.

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post #3 of 10 Old 01-13-2001, 04:59 PM
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I can't help thinking you guys may be underestimating the effect of distorted geometry using a curved screen with the digital projectors. With my 120" screen, I find that the curve introduces about 3" of barrel distortion. This is not subtle. If the projector is mounted anywhere other than screen center height, there will also be "bowing" of the image and keystone distortion.

Peters idea of actually constructing the screen in a barrel shape may partially solve this, but I think a non rectangular screen would be a hard sell for most of us.

You are right about the acoustics. Its like one of those old "Big Ear" spying toys. If the room is relatively dead and no speakers are firing right at the screen its OK though.

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post #4 of 10 Old 01-13-2001, 11:41 PM
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Yes,

Make no mistake, the TORUS is a special screen for a special application. There are great benefits to be had and there are likewise disadvantages. Geometry distortion and audio hotspotting are two I have heard about, their degree and how effectively they can be dealt with is a question to ask Gerald Nash when he, hopefully, joins our forum. It is imperative that people are made aware of the tradeoffs they make when they buy a TORUS screen, just like hotspotting on high gain screens, it will not deter buyers if they are properly educated. Instead it will ensure that they are not disappointed by their experience and that the screen fits their application.

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post #5 of 10 Old 01-14-2001, 05:44 AM
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Hi KFung

The 5" number in my previous post should have been 3". It has been corrected.

That's still a lot of uncorrectable distortion to try to "educate" people into accepting. You can approximate it yourself with a crt projector and flat ~8' screen. Just lower the pincushion controls until there is a 2.5" or so difference in width top to middle and see what you think. It is unnatural and distracting.

My guess is that, with respect to the digital projectors, anything other than near perfect geometry would be a very hard sell. If more brightness is needed, it might be better to just buy more lumens rather than go to a curved screen.

Mike


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post #6 of 10 Old 01-14-2001, 08:21 AM - Thread Starter
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If there is enough interest created in the proper areas.. then a screen design will appear. Once that occurs, then a lens adapter for digital projection systems can actually be formulated along the lines of a 'standardized' consideration. No lens manufacturer will begin making considerations towards such a unit until there are some actual basic design consideration specifications to hang a model on.

It's the chicken-and-egg scenario as usual. No one will commit until the other does. In this case, because the screen can actually be used by CRT owners without any real problems..... it is just ironic to note that it will probably be CRT users that create the initial point that allows this whole thing to come into being, that in turn ends up bringing such a screen to digital projection systems.

It is not a good idea to 'stack' adapters on a lensing system, as the losses due to the physics of 'barrier sciences' can end up being a serious problem. Loss of contrast due to to many lens elements is not along the lines of a proper solution. It is my understanding (I don't really know the answer to this) that the better digital projectors tend to use a similar mounting system (ie. standardized in some fashion), so it may be feasible to come up with a standardized adapter. In the PROPER application, it would be best to combine the characteristics of an anamorphic adapter with that of correcting for the distortions encountered with the Torus screen design. A 'single element' solution may be impossible to produce... I do not know enough about the problems surrounding each. The elements will PROBABLY have to be stacked, which will quite likely remove the usage of cheap materials from the agenda. Highest contrast must be maintained. It's the multiplicity of stacked elements that will kill the thing at the start. The differences might be minor, but hey, why not go whole hog?... I don't know the lens market, and what design considerations are available today as solutions. Perhaps an acceptable lens system IS achievable at a relatively decent price.

This is the other half of the recipe that must be looked into at the same time as this screen emerges.

The curved screen will have the double benefit of allowing for higher gain materials.... due to the lack of hotspotting.. this gives a higher (highest available) contrast range due to the rejection of ambient light problems. The curved screen surface itself, as a design consideration, brings about a very high inherent ambient light rejection characteristic. What this does, is give the image a punch that rivals that of a direct view CRT.... And you cannot beat that with any kind of a stick. The screen is suddenly no longer the limiting factor. The contrast problems are pushed back to where they belong, directly onto the problems inherent within the design of the projector.

Most folks DO NOT understand this simple fact... the screen/room- situation/combination is one of the major factors affecting the contrast ratio they get out of their systems. The other, of course, is the projection system itself.
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post #7 of 10 Old 01-14-2001, 08:20 PM
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Mike,

I might agree with you for digital projectors, sometimes buying more lumens is pratical. But keep in mind that most contemporary theaters (at least in my area) use horizontally curved screens with a sizeable curvature, mostly to obtain better focus on the screen I believe. In any case, when the sides of the screen are masked and you're not showing computer graphics it can be very difficult to identify geometrical distortion. The curvature on your screen is probably going to be different than any final product and the distortion may not be as severe.

On the other hand, for CRT projectors with their advanced image controls, geometry distortions are controllable and the lower light output of a CRT makes them better suited for a TORUS. Most people would consider a TORUS if the alternative was a dim image, a high gain screen with a hotspot, or double stacking that $20k+ projector. All of these solutions have their drawbacks and advantages, just like the TORUS. It all depends on what you value and what you can compromise on (or maybe you want no compromises... <cough> DTS theatre at CES <cough> ).

On KBK's idea of a custom lens, it's not a bad idea and it would certainly solve many of the problems with the TORUS. However, like you said it is a chicken and egg kind of situation and even worse it is probably not economical. It may be that a range of curvatures better suites the market for the TORUS and in that case there would need to be multiple lens types. Besides custom glass to correct geometrical distortion like that would be rather expensive for the consumer to buy, they would probably buy more lumens instead...

Regards,

Kam Fung
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post #8 of 10 Old 01-15-2001, 05:28 AM
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I currently have a Vutec curved screen (purchased from Joel Cohen at Hi-Rez Projections - no affiliation other than satisfied customer). The URL for their screens is http://www.hometheater1.com/, then click on Screens from the menu on the left. I don't know if it's a toroid shape or not though, but it's curved both horizontally and vertically. I can take some measurements if anyone is interested. The corners are about 3.5" forward of the center of the screen. I believe that the surface has a gain of 12, but the new ones are ultra high gain Al foil with a gain of 13.2 Here's my setup for the following observations:

9" tube Sony projector. Made in '89, no burn in, digital chassis/convergence
Ceiling mounted projector, directly over the main viewing position, 11' throw
Small room: 11'x12'x7.5', white ceiling, light carpet, lots of light reflecting surfaces
70"x52" high-gain curved Vutec screen
Room can be completely darkened, but my wife likes a little light on
ATI All-in-wonder Radeon powered HTPC

Observations:
1) The screen is silver with no texture. I use a swiffer (synthetic dusting cloth) to dust it and diluted Formula 409 if it gets really dirty.
2) It's bright! I don't have any way of measuring it, but the 11 year old tubes still put out a lot of light
3) The center is brighter than the corners. I believe that's because I'm not sitting at the focal point of the curvature.
4) Flat field full white shows a slight color shift - the right has a very light blue tinge and the left is slightly red. I think there's a vertical green tinge directly in the middle, but it's so light it's tough to see. None of the aforementioned are even slightly visible while watching any program material.
5) While displaying flat-field full-intensity white, a paint chip of Baer's Ultra Pure White satin paint (the brightest Home Depot sells) looks mid-level gray compared to the screen. I can take a digital picture for comparison if anyone's interested
6) I can barely converge the projector to handle the curvature of the screen, but when it's right, the image is perfectly rectangular from my viewing position (on-axis). The further you go from on-axis, the more the curvature becomes apparent.
7) Audio is a problem. Whispering in the main seating is really amplified and there was a lot of reflection between the screen and the hard wall behind the main viewing position. 4" of Sonex wrapped in black felt hanging away from the wall behind the main viewing position helped significantly.
8) Light reflection off the back wall was a problem as well. The black bands from letterboxed movies became noticeably brighter than the black wall behind the screen when the average picture level was high. The problem was light reflecting off the back wall back to the screen. The black felt around the Sonex helped considerably.
9) Off-axis light rejection is excellent

I'm considering a larger, 16:9 screen to replace the current one. I'd buy the larger curved Vutec, but I'm concerned that I may not be able to converge the projector for the curvature in the corners at 80" wide.


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post #9 of 10 Old 01-15-2001, 07:39 AM - Thread Starter
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I suspect then, that there would have to be a minimum of three lens elements to get the job done on a 'universal adapter' anamophic, and h/v geometry correction. I do not know how the elements are set up to do the anamorphic, I suspect there are two elements... That would be a total of four... A bit cost, and design prohibitive, to say the least. I am sure it can actually be done, but how may would have to projected for purchase by the buying public to make it a workable enterprise?

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post #10 of 10 Old 01-15-2001, 07:16 PM
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The Vutec screen is a compound curve screen with no formal pedigree in ray tracing design. In other words it, like the former Schudell, and the former Beiner screen were conceived prior to ray tracing software.

Although the image is bright it will not have the perfection in image luminosity evenness that a Ray traced compound curved screen will have. When that is acheived the images seems to float in 3d space.

The acoustical problems of the TORUS screen are limited to sounds that bounce off the screen back to your ears. I can attest that having heavy drapes on both sides of the screen, with a heavily padded rug, fluffy furniture and the same heavy drapes on the backwall eliminate all acoustical hotspotting by 99.5%. The contrary is true if you do not use padding but only on very large screens. Wider than 11' and in aspect ratio closer to 1.33. The closer the screen is to 2.35 the less noticeable the acoustical curiosity (it is not a problem) would be evident. The curiosity can be described as hearing your own voice in a totally out of phase "from inside your head" reverberation and it only happens when you are chrouched talking to the center of the screen. It also has happened with dipolar horn speakers aimed at the screen.

Back to the Muffled room:his .5% IS NOTICEABLE only in a very narrow V/H axis with a very large screen.166 diag. On sizes of 54 x 96 the reflections are not an issue.

The silvery surfaces tend to detract from the benefits of the custom designed compound curved screens. A material like the pearlescent gray screen may however work well, since it would preserve the basic whiteness of the whites while increasing the blacks. A screen like the vutec would benefit with resurfacing with a pearlescent screen in the 2.8 gain.

I am curious to see what a completely flat screen surface would lok like in such a Custom Designed Solid Compound Curved Screen. CDSCCS ?!

I believe that the use of this term is preferred by Gerald Nash as the TORUS is a patent that involves a suction type screen. He will make that clarification like he made to me the other day. If it does not suck is not a Torus..

No doubt that the easiest projection technology to build these screens for is three tubes. With such projectors the test grids are perfectly horisontal and vertical.

However the Torusses are widely used with 35 mm 2x anamorphic lenses in AMC cinemas with no distortion and also conveying the same "floating depth effect".

The Isco /Schneider may be inducing its own barrel distortion, I don't know for sure. But it is safe to say that these solid ccs screens should be designed for anamorphic aspect ratios 16 x 9 and 2.35.

Why 2.35 because the Schneider Cinema lens will work on many dlp's and dila's, lcd's. Also such as screen can be concealed in a pop up even if 100" wide.WAF factor.
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