CurtPalme.com Home Theater Forum

[armstrr]

so when you are sitting, what is the distance between your eyes and the center of the tubes?

did you go 1:1 or 16:9?

or put another way, what is the distance from the floor (or riser if its under) to the tubes center. i have visions of the back row seats staring at my moome hdmi input card. now, i (and i'm sure some of you....) could stare at it for a while, my kids wouldn't find it as interesting!


my last screen was a diy torus and while the price was right and it performed well (minus a few streaks....) i have other things to finish. AND an electric screen would be cool!

does it have a trigger? if so, how does one wire for that?

THANKS

[Zebu Fellenz]

armstrr,

Can you tell us a little about your DIY torus, what material did you use and with what projector? I've wanted to do a torus but I've heard that it won't work with my G70 mounted on the ceiling.

Thanks,

Erik

[armstrr]

i used a marquee 8500. worked like a charm as it would with your g70. do a search on avs for armstrr as the poster. i documented the process. let me know if you can't find it.

[garyfritz]

Here's one of armstrr's posts: http://archive2.avsforum.com/avs-vb/showthread.php?threadid=467141
You can also use -Pjackso's spreadsheet to calculate your curves: http://archive2.avsforum.com/avs-vb/showthread.php?p=5627244&&#post5627244

I've got some other torus threads bookmarked if you want 'em.

[Zebu Fellenz]

Thanks for the link Gary.

Armstrr,

Are you saying that the torus worked fine with the projector overhead? I always thought the projector had to be floor mounted due to the way the light was reflected, or is that with high power screens?

Thanks,

Erik

[garyfritz]

(Sorry, got pulled away when I was editing that response -- there's another link there now)

Yes, that's high power. HP is a retro-reflective screen, so your eye has to be close to the light source. Tori use angular-reflective screen materials. Ceiling-mounts work fine.

[Bruce 09]

[Zebu Fellenz]

Thanks for the clarification guys.

So the Vutec Pearlbrite is an angular reflective surface, right? I'll have to start doing some checking and see what I find. I remember some people having streaking issues with the Pearlbrite.

I'm also considering dropping the torus idea and just going with wilsonart, but if it looks like I'd get enough brightness benefit with the torus I'll probably end up going that way.

Erik

[deronmoped]

armstrr

My eyes to tube distance is 40", I'm going to raise my chair a little, maybe get a platform to put it on or just get a chair that puts me up higher. I only dropped the PJ down off the ceiling by a foot, I put it just above where it would hit my head while standing if it was lower. Once your eyes get within a couple of feet of the PJ the brightness is about as much as it's going to get.

The screen came with a up down toggle switch, that you wire to for 120 VAC. There are plenty of devices out there that you could control the screen with.

16X9 screen, 159" diagonal

Chad

I sit about 16' from the screen.

I though color shift would be a big deal after seeing how badly this screen does it, but after using it for a while I have no objections. It's just one of those things that you know in your mind is there, but you can not see it not unless you want to run laps around the room while watching a movie. Anyways the best seat in the house is perfect, it's the same problem you have with any audio system, there is usually only one really good seat and that is reserved for the "King" "It's good to be King".

Deron.

[VideoGrabber]

Back in April, Chad asked:
> How far away do you sit from the screen? <

The 16' Deron mentioned is a big part of why this works for him. Closer viewing distances won't demonstrate as much gain, and it's all due to the angles. With Deron's 40" eye to tube distance, coupled with on-axis viewing, he's got an approximately 11.8-deg angle. That puts his gain around 1.8, with no hot-spotting. Raising his chair can push that considerably higher... possibly close to 2.5, certainly at least 2.2.

> I'm thinking of using an 80" wide (92 diag) HP in a very small theater room. My eyes will probably be around 88-90" from the screen. <

A 7.5' viewing distance will make it difficult to keep the angle small, because even with the PJ close overhead, the angle is still relatively large.

> I'm wondering if the color shift will be objectionable even on the sofa <

Not so much for the central seat, but somewhat for the side seats. Since it's constant, as Deron indicated, it may be easy to overlook.

> (the seating area is 75" wide). I'm considering having the PJ sit on a shelf right behind the couch firing a foot or so over my head. <

Well, since you said "a foot or so", let's run the numbers with it at 12" and 18" overhead. We'll put your eyes at 90" to get the best results. Center seat on the couch will be 10.7 and 14.4-degrees, for those clearances. These translate into gains of 1.9 and 1.5, and the reason such a small change in the height makes such a big difference is the very short viewing distance.

For the 2 side seats on the sofa, things aren't so good. Each is ~2 foot off-axis, so the compound-angles will be 18 and 20.7-degrees. The gains there will be ~1.1 and 0.9. So Deron's "only one really good seat" definitely applies here in this close-viewing scenario. Not that a gain of 1.1 is bad. And the uniform illumination is a plus. But it's a big drop from 1.9.

The color shift that Deron refers to results from the fact that the HP sends light back to it's source, and with a CRT, there are 3 sources, separated by 7-8". There are some real advantages to the HighPower screens, but uniformity of audience experience isn't one of them. They also work better with single-lens (aka, digital) PJs.

For your situation, Chad, if you're looking for gain, something like the VideoSpectra might be more appropriate, with center seat gain at 1.5, and side seats at 1.3. Plus there won't be any need to drop the PJ so low, and the material will be less expensive than the HP.

Also, with a screen that size, gain isn't nearly as important. Deron has 3.3x times as much surface to light up as you. Look at it this way... based on the relative screen sizes, even if Deron raises his seating to achieve a 2.2 gain, if you had just a unity gain (1.0) screen, it would still be 1.5x times as bright. Size costs.

[armstrr]

[armstrr]

would this material be ok to mount on a home made frame? is it "stretchy" at all? my only reference is pearlbrite which has a consistancy close to electrical tape!! (ok, not quite...)

would i be better to order the fabric or order a model b or c and cut it?

thanks!

[deronmoped]

As far as getting the HP material, it is cheaper to buy the whole electric screen. I even asked the sales person why that was and she said, that's just the way it's priced, no real explanation.

I have come to the conclusion that you really do not want a fixed screen. Fixed screens have no protection from dust and kids and people that are too stupid not to touch it. You really do not to have to clean a screen, some screens show up the slightest imperfection and you can cause imperfections from cleaning it.

Deron.

[VideoGrabber]

> I thought color shift would be a big deal after seeing how badly this screen does it... <

Deron, it would be good if you could expand on this. I doubt many have had a chance to see a HP with a CRT.

[garyfritz]

I have -- a friend has a G70 and a HP.

The HP is retro-reflective. That means that the screen gain is higher as your eye gets closer to the light source, like a stop sign.

This works great for single light sources like a digital pj. But a CRT has THREE light sources. Unless you sit directly under the CRT, you will be significantly closer to some tubes than to others. For a floor-mounted CRT (like my friend's), you sit on one side or the other. This means you are about 15-18" closer to the R than the B, or vice versa -- which means you have higher gain on that closer color. So on the "red" side the picture has a red push, and on the "blue" side the picture has a blue push.

It's not horrible. As Deron said, you probably won't notice it unless you go from side to side and look at the difference, or unless you're really hypersensitive to proper color balance. But it's definitely noticeable if you move back & forth.

[VideoGrabber]

Thanks, Gary. I was aware of your first 2 paragraphs (see my comments a few posts up), but your 3rd paragraph was the subjective evaluation I was looking for. That's kind of pivotal information for any CRTer who might be considering it.

I knew the differential chroma push was there, just not how perceptually significant it was. I think your comments summarize it pretty well. Thanks again.

[armstrr]

i'll be sitting directly under the pj. i don't know any videophiles who will nitpick my setup. all visitors will be wow'ed and enjoy it. and since i'll be in the money seat, i'll be happy too!

[garyfritz]

How far under the pj? I tested HP in my (ceiling-mount) setup, and it looked *awesome* if I stood up -- but no better than blackout cloth if I sat down. Your eyes have to be fairly close to the lenses to benefit from HP. My pj was hanging from a 7'10" ceiling so it wasn't all that much higher than my sitting position.

[Advent Videobeam]

Advent's 1000A screen was aluminum, was dull surface and retro reflective, funny how things go full circle Same concept, there's a viewing sweet spot and other angles are reduced brightness Looking at this post and considering options if fabric in screen posts doesn't work Screen quality is still important for best projector performance. I''l post some pics when my R2 unit get calibrated!

[Advent Videobeam]

Advent's 1000A screen was aluminum, was dull surface and retro reflective, funny how things go full circle Same concept, there's a viewing sweet spot and other angles are reduced brightness Looking at this post and considering options if fabric in screen posts doesn't work Screen quality is still important for best projector performance. I''l post some pics when my R2 unit get calibrated!