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Discussion Starter · #1 ·
I have been wondering how high the screen's gain can be with a ceiling mounted projector.


I guess a typical livingroom is 2.5-3.5 meters high, projector is mounted somewhere above your couch in the ceiling and viewing distance to screen could be 4-5 meters.


Even in the best situation the angle between viewer and the projector is around 20 degrees, usually more. When I examine the gain-charts that screen manufacturers provide, it can be easily seen that pretty much every screen has fallen to gain 1 or lower with 20 degrees. This includes the mild 1.3-1.5 gain models.


Because of this, the point of any high gain screen seems to be lost if I can't have my projector on or in a table in front of couch. Obviously the best location for your projector would be right on your lap which is especially painful for us CRT owners :) .


Is reality so much different from what I can understand from the graphs or am I just missing something? What I am interested in is only the picture brightness, not the possibly smaller problems with light reflected from screen to walls and ceiling if one uses high gain materials.
 

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Yep, High Power screen from Dalite needs table top mounting to get its full 2.8 gain due to its retro-reflective nature (bouncing light back toward PJ). For ceiling mount, your best bet is the cheaper Dalite Video Spectra with 1.5 gain which is reflective (bouncing light at equal angle of exit as entry from perpendicular line to screen center).
 

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Discussion Starter · #3 ·
Well, I guess I happily forgot that some screens are reflective and some retro-reflective. But how can I tell the type of a screen? I have Da-Lite's and Draper's brochures, but I don't recall seeing any information about reflectivity.
 

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Saurama,


Excellent question.


All screens have normal reflectivity except the glass beaded screens which includes the hi-power (has microscopic beads).


To my knowledge the only big company that is making beaded screens is Da-Lite. All other companies use "sparkles" or glossy satin-like coatings to achieve normal reflective gains.


There is still some benefit of using a retro-reflective screen with ceiling mount applications but not nearly as much as table-top. (For table-top, retro-reflective is the only way to go when you need high gain IMO.) You will still get some gain probably about 1.2-1.4 depending on the screen and you will have excellent uniformity with retro-reflective. Uniformity of high gain normal reflective screens can be a problem once your in the 1.8+ area and/or used with short-throw applications.


What we really need is a hybrid type screen that possesses a combination of retro and normal reflective properties. That way the brightest output from the screen is ALWAYS straight back to the viewer who is on level with the screen height regardless of projector position. There might be a company working on this ;) but don't hold your breathe


-Mr. Wigggles
 

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Mr Wiggles,..............don't get me started............
 

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Discussion Starter · #6 ·
MrWigggles, thanks for the info. I think I can after all go for a 1.3-1.5 gain screen and get the extra brightness. KBK's goo is a good choice again. Glass beaded has not been a relevant choice because I don't think I need +2 gain anyway.


This also makes understanding torus a lot easier. As far as the screen is not a glass beaded type it is a normal reflectice, even the ones that have gain in range 2-4?


Your idea of a screen that is on viewers level and puts most of the light straight ahead is interesting, but it does have problems audio-wise. Of course a picture starting almost from floorlevel is easier to watch than one that is very high. The problem rises if you want to have the center channel speaker on the same level as main speakers ie. you want to have a no compromise sound for multichannel music.


Center channel (identical to main speakers) can be about one foot below the level of main speakers max. This is if you want absolutely integrated soundfield in the front sector. If listening distance is short or all three front speakers are very close together, even one foot is too much. This is a typical sized finnish livingroom in my mind and they are not especially big.


With movies you can live with perforated screen and attennuated highs but not with music. Only choice is to get three front speakers pretty much in level and mount the screen above them.


If I sit on my couch, my head is about one meter from the floor. If I want to have a no compromise multichannel music systems, I must have high quality true full range speakers in front and they rarely are less than one meter high.


Well, this is a bit off topic. Just had to remind that picture is one half of a good audiovisual experience, sound is the other half :) This of course means the screens lower edge can't be too close to floor and the viewer would lose all the extra gain.
 

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Saurama,


I have never seen a glass beaded screen advertised as less than 2.0 gain. However, normal reflective screens can have gains ranging from 1.1 to over 10. The higher the value the more mirror or silver-like the screen gets.


I don't mean to suggest that your set-up be really low at all. In my set-up my eyes are at the bottom edge of the screen which is where my speakers are. The general rule of thumb is that none of your seating positions should have peoples eyes higher than 1/2 the screen height or below the bottom edge. 1/3rd the way up the screen is supposed to be the ideal. The hybrid screen would simply be useful any typical set-up.


-Mr. Wigggles
 

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I agree with Saurama in the necessity for placing the center BEHIND the screen. Since my HT was triggered by visits to IMAX theaters my screen starts right at the floor and extends to full ceiling height (basement, 2 meters height). This way I sit exactly centered to the picture and really like this setup a lot.


Saurama triggers a question I had for a while: why can't you have two center speaker in such a configuration, one above and one below the screen? When properly set, the sound should sum up to a monaural signal exactly at ear height, essentially a vertical phantom speaker. This would be the ideal solution ?!


Any comments ?
 

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Hi,


I am no techie. So if I am full of it, please don't hesitate to correct me. I remember reading a review of the Sony G90 in SGHT. the g90 was put on the floor shooting up at the screen. To see the brightest picture, the viewer would have to stand up as Joel Brinkely explained. If it were ceiling mounted as per your question, to see the brightest picture off a screen with a gain above 1.00, the viewer should be at the optimal reflection axis, which would be sitting down.


Ben
 

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Quote:
Originally posted by ThomasR
I agree with Saurama in the necessity for placing the center BEHIND the screen. Since my HT was triggered by visits to IMAX theaters my screen starts right at the floor and extends to full ceiling height (basement, 2 meters height). This way I sit exactly centered to the picture and really like this setup a lot.


Saurama triggers a question I had for a while: why can't you have two center speaker in such a configuration, one above and one below the screen? When properly set, the sound should sum up to a monaural signal exactly at ear height, essentially a vertical phantom speaker. This would be the ideal solution ?!


Any comments ?
Thomas,


I think it is a decent idea. However, since there are two point sources, you will get some addition and cancellation at certain frequencies. The result will probably be voices that are very "full" sounding like they are coming from your room and not as much from the movie.


if you can't have a perforated screen it might not be so bad. Also, I wouldn't count out your audio sounding horrible even if your screen isn't perforated. I would give it a shot.


-Mr. Wigggles
 

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Quote:
Originally posted by BenjaminWoo
Hi,


I am no techie. So if I am full of it, please don't hesitate to correct me. I remember reading a review of the Sony G90 in SGHT. the g90 was put on the floor shooting up at the screen. To see the brightest picture, the viewer would have to stand up as Joel Brinkely explained. If it were ceiling mounted as per your question, to see the brightest picture off a screen with a gain above 1.00, the viewer should be at the optimal reflection axis, which would be sitting down.


Ben
Ben,


You are correct for normally reflective screens. However, retroreflective screens behave in an almost magical way. The most amount of light comes back to the source no matter what the angle the light actually hits the screen.


-Mr. Wigggles
 

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Kfung,


You are correct, but the off axis viewers will still have gain in the 1.0 area at least without any hotspottng.


With a retroreflective screen, as you move around the room, the whole screen goes up and down with intensity. Whereas the normally reflective high gain screen will have a hot spot that follows you as you walk around the room.


-Mr. Wigggles


Ps. I'm sure you knew most of that I'm merely reiterating it.
 

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Does this make you wonder why.................we bother with reflective screens at all ?...........................why glass beaded screens are constantly thought of as old technology good for slide projectors and not suitable for video projection?

The fact is and everyone knows it , whether they want to admit it or not, that modern retroreflective screens with super fine beads can produce an incredible image - without a hot spot that follows you around the room and without edge fall off. They are the most efficient screens possible where maximum light return is required. Yet we still ignore this, ceiling mount our projectors to make sure that a retroreflective screen will be useless, and project our images on to a white ''sparkly'' screen so that we can illuminate our theater walls instead of our retinas.
 

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Mr. Wiggles,


You're right, of course, pound for pound a retro-reflective screen should give a more uniform image than a conventional screen of the same gain. I just worry about the high inherent gain. If you are pushing it enough that you need the high gain, the fall-off might give an unacceptably dim image for those in close seating or at the edges. Of course it's still better than a conventional high gain screen. Just thinking about it a little more made me realize that a closer throw is probably better in a lot of cases for a retro screen, rather than the long throw for a conventional screen because it distributes the light to the audience on the sides a little better at the expense of some uniformity. The only beef I have with the retro screen is that for optimum performance the projector usually has to take the best visual seat in the house. :-/


Ziggy,


I would agree with you for applications where you need to high gain for an acceptable image, but if you don't you can possibly do better with a low gain conventional screen.


Regards,


Kam Fung
 

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Quote:
Originally posted by KFung
Mr. Wiggles,


You're right, of course, pound for pound a retro-reflective screen should give a more uniform image than a conventional screen of the same gain. I just worry about the high inherent gain. If you are pushing it enough that you need the high gain, the fall-off might give an unacceptably dim image for those in close seating or at the edges. Of course it's still better than a conventional high gain screen. Just thinking about it a little more made me realize that a closer throw is probably better in a lot of cases for a retro screen, rather than the long throw for a conventional screen because it distributes the light to the audience on the sides a little better at the expense of some uniformity. The only beef I have with the retro screen is that for optimum performance the projector usually has to take the best visual seat in the house. :-/


Ziggy,


I would agree with you for applications where you need to high gain for an acceptable image, but if you don't you can possibly do better with a low gain conventional screen.


Regards,


Kam Fung
You are correct about having a sweet spot.


The width of my couch is the sweet spot with aproximately 30FT-L for peak white; but the viewer will still get 15FT-L+ from the seats on the side. However, after seeing 30FT-L no one wants to sit on the sides!


I do wish that my hi-power was closer to a gain of 2 with a wider viewing area nstead of the roughly 2.5 it is now (the 2.8 rating is little bit of a stretch). I have never seen it in action but I wonder what the "Wide Power" is like. It comes with very few mounting options and isn't in the sample swatch packet that Da-Lite gives out.


-Mr. Wigggles
 

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Yes... a lower gain retro-reflective screen would be really interesting... or even better one that behaves like a retro-reflective screen in the horizontal and like a reflective screen in the vertical. You could have your cake and eat it too with a ceiling mounted projector.


Kam
 

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KFung,


Agreed completely. I love my high-pwer but there is always room for improvement.


-Mr. Wigggles
 
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