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To curve or not

21K views 127 replies 38 participants last post by  Vern Dias 
#1 ·
I've been thinking more about getting a curved screen as of late. In speaking to Stewart about it, only about 1% of the screens they sell right now are curved. However, they expect to see a huge increase in curved sales, possibly getting as high as 20% of their business within the next year or two.


I also understand that Dennis (HT guru) installs a ton of curved screen in higher end rooms.


As I understand it, curved screens work particulary well with scope set ups (another huge trend) and with higher gain screens but if I'm misguided on this, please let me know.


I'm trying to fully understand the benefits and drawbacks of such a set up and that is what I would like to have this thread discuss. Let me start with some comments and questions. I'd really like to hear from those that have a curved screen or have seen one.


The benefits I see with the curved screen are as follows:

-reduced hot spotting with gain screens

- screen curve avoids cross reflection (all projected light is transmitted to the audience)

- looks "cool"

- improves image uniformity


Drawbacks?

-Added cost

-difficulty in figuring out optimal curve radius

- not sure about impact on viewing cone - expand it from the far side but reduce it from the near side?


Miss anything?
 
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#52 ·
I don't have a curved screen, and if I did it would be empty because I don't yet have a projector either, but I have been lurking in the constant height forum for a while and would eventually love to have a CH setup. I do however have a very basic understanding of the physics of light and the way a projector works (at least the physical lighting aspects of it.) Feel free to corect me if I'm wrong, actually, please corect me if I'm wrong, but here is what I think.


Just based on what I think the physics of the situation is, I would think that the radius would be the same as the throw distance from the projector. The point being that all the light would then be traveling an equal distance from pj to screen and it would all be hitting the screen at a perpindicular angle. Obviously this is less true with a single axis curve than it is with a torus, but that seems like the basics principal to me. If I am correct about the radius, then the hotspotting should never be a problem. Of course I am talking in a strictly hypothetical situation, and because the projectors have been built to look OK on a flat screen you are dealing with two solutions to one problem which will often add up to a mess. That last part makes me wonder... when you use a curved screen, do you have to do extra processing to make the image square again or can you turn off the processing that the projector has built in?


Just my thoughts and questions,

Brian


Edit:

I think Mark and I are saying roughly the same thing, aparently at the same time too.
 
#53 ·
Brian:


In most cases, the radius is working out to be about double the throw distance, or slightly more (and, I don't recommend everybody running off and just doing it this way..please). The projector and lens system is designed to provide a non-distorted image on a flat screen with no visible lack of uniformity. The addition of an anamorphic lens (deliberate distortion of the image) can add a pincushion effect...this effect is eliminated along the horizontal axis with screen curvature. Beneficial side effects of the curvature include: (1) more of the reflected light is directed into the seating locations (where it is useful) and less onto the walls; (2) this brings more uniformity of the image into the seating locations; and, less hotspotting when higher gain screen materials are used.


The radical curvature you suggest would work for a single seating location which would happen to be at the projector lens. We're dealing with a larger seating area where picture uniformity is desired. We don't want viewers at the left and right extremes of the seating area to have a distorted image either.
 
#54 ·

Quote:
Originally Posted by Dennis Erskine /forum/post/0


Brian:


The radical curvature you suggest would work for a single seating location which would happen to be at the projector lens.

Yes. Why not just look directly into the projector for that truely widescreen experience. (DO NOT ATTEMPT THIS YOU'LL BURN YOUR RETINA OUT AND THEN BE SATISFIED WATCHING A DLP!)
 
#55 ·
"The projector and lens system is designed to provide a non-distorted image on a flat screen with no visible lack of uniformity. The addition of an anamorphic lens (deliberate distortion of the image) can add a pincushion effect...this effect is eliminated along the axis with screen curvature."


Does this happen due to the fact that cinema lenses disperse light uniformly from the centre and HT projectors work from one plane, either the bottom to top (shelf mounted) or top to bottom (ceiling mounted)?


During my research, a cinema installer informed me that I would have to bow my screen when using a domestic display device instead of a commercial one...


Mark
 
#56 ·

Quote:
Originally Posted by CAVX /forum/post/0


My understanding is that the curve is to ensure that light reaches all parts of the screen at the same time.

Mark, you have to be kidding, right? Light travels 186,000 miles per second. How much of a time difference is 6" going to provide? I seriously doubt you can even find much in the way of equipment that could measure such a small difference in time.
 
#57 ·
Dennis,


Thank you for the clairification. You are a fountain of knowledge.


Thanks,

Brian
 
#58 ·

Quote:
BTW, if you're using a Screen Research screen, take a piece of 1" fiberglass, cut to the outside size of the speaker, cut cutouts for each of the drivers and install on the face of each speaker.

Dennis, whats the best way to attach the fiberglass to the cabinet? Put screws through the fiberglass and attach to the front grill clip holes?
 
#60 ·

Quote:
Tukkis:

I use black electrical tape all the way around the cabinet on the top and the bottom just to keep it in place (and not damage the speaker cabinet for a future eBay sale).

Thats sounds like the best option.


Sorry to hijack the thread, but for mounting speakers behind the screen, is it recommended to treat the screen wall?


Also for mounting the front three speakers. On stands? Hang off screen wall? On some sort of platform?


Thanks
 
#62 ·
Thanks Dennis.


One final question: Is the best height for the speakers behind the screen dead middle? So the center speaker is in the middle point of the screen?
 
#65 ·
Because the implication is that the correct screen position has the vertical center of the screen at the same distance from the floor as your eyes/ears when you are seated in your chair, correct? Or are you recommending that the tweeters fire over the top of your head?


I ask because in a "real" movie theater, from a seat one-third back, you would be sitting substantially lower in relation to the screen's height.
 
#66 ·

Quote:
Originally Posted by HiFiGuy1 /forum/post/0


Because the implication is that the correct screen position has the vertical center of the screen at the same distance from the floor as your eyes/ears when you are seated in your chair, correct? Or are you recommending that the tweeters fire over the top of your head?


I ask because in a "real" movie theater, from a seat one-third back, you would be sitting substantially lower in relation to the screen's height.

In HT, one would aim to have both the eye line to centre of the screen and ear height to the tweeters to be the same. This might require the speakers to be tilted up and or the installation of risers to elevate the seating.


Even speakers with Controlled Vertical Directivity can be set up so that the sound covers most seating positions as the sound dispersion becomes wider the further away from the speaker one sits.


In a well designed commercial cinema, one third back should now have you centre of the screen thanks to "stadium" seating. Just my $0.02 worth...


Mark
 
#67 ·
Does a curved screen have any impact on Moire, good or bad, if you use a perfed screen? Does it depend on size? If so, assume a 10' wide scope screen
 
#69 ·
[Once you have an anamorphic lens, you won't have moire.[/quote]


What about when you're bypassing/removing it because you're watching 1.78 material?
 
#70 ·
I've spec'd out the appropriate radius, frame and screen gain needed in my situation with Don Stewart's help and DE's encouragement and am just waiting for the quote. The width of the screen will be 123" (scope). I've decided to not perf the screen and it will get a 1.5 gain. Be sure to check out the different frame options if you ever decide to do this.


I found this link interesting because it gave a simple yet convincing argument in favour of curved screens

http://www.mdicinema.com/en/tools/ga...ed_screens.htm
 
#71 ·

Quote:
The correct screen position would have the primary seat 12 degrees below screen center and the top no more the 30 degrees above eye level for any seat.

So 24 degrees from eye level to top of screen? Seems alot of Home Theatre?
 
#72 ·
If I understand Dennis' comment, he is saying that for the money seat, the center of the screen is 12 degrees above seated eye level. That jives with my rule of thumb I have used in the past to install the screen so that MFVs eyes are 1/3 to 1/2 screen height from the bottom of the screen. (See the next post, now I think it might not jive with my previous experience) IOW, when you are seated in the best seat, your eyes should be between 16" and 24" up from the bottom of a 48" tall screen. That way, your neck isn't straining looking up too much and you still have a nice cinematic feel.


The second part about 30 degrees means that no seated viewer (even if the primary seat isn't in the front row) should have to look up more than 30 degrees from horizontal to see the top of the screen. I agree that is a lot. It makes sense for that to be a worst case scenario, not necessarily a recommended vertical viewing angle.
 
#73 ·
Dennis,

I have been doing some cipherin', and the 12 degree subtended angle seems extreme to me. Staying with my example of the 48" tall screen, that would put eye level 3.9" below the bottom of the image. Am I misunderstanding your post? Is my math incorrect? I was just using (tan12degrees)*(viewing distance)=vertical displacement. This gives approximately 27.9" of elevation from eye level to the center of the screen for what you have described as the primary seat. What am I missing?


Also, with a constant height setup, and assuming the ideal 36 degree HVA for 16:9, this makes the max vertical angle from the primary seat work out to 21.58 degrees. ArcTan(51.9/131.25)=21.575 degrees, so that's well inside the 30 degree worst case scenario.


I am just trying to understand the combination of "ideal 12 degree subtended vertical angle" with the idea of having eye level between the middle and bottom of the screen height. Unless I made a mistake, it appears the two are mutually exclusive and contradictory goals.
 
#74 ·
I'm even more confused now.


Seems anywhere between 10-20degrees seems comfortable.
 
#75 ·

Quote:
Originally Posted by HiFiGuy1 /forum/post/0


The second part about 30 degrees means that no seated viewer (even if the primary seat isn't in the front row) should have to look up more than 30 degrees from horizontal to see the top of the screen. I agree that is a lot. It makes sense for that to be a worst case scenario, not necessarily a recommended vertical viewing angle.

I read somewhere (some SMPTE guidelines or maybe on the THX website?) that in a real cinema the worst case scenario is 45 degrees from the front row to the top of the screen.


That's a bit extreme if its right, but as we would not have more than 3 row in a HT, 30 degree from the front row might still be be OK with less being preferred...


Mark
 
#76 ·
CAVX,

With a 45 degree angle from the front (worst) seat, you don't even have to do math to realize that this means the vertical distance from the top of the screen to eye level is EQUAL to the horizontal viewing distance. Sitting 15 feet away means having the top of screen 15 feet over your head! Talk about a neck-strainer! That is definitely one of the theater guidelines that is only appropriate for commercial cinemas.



The 21.58 degree viewing angle to top of screen I posted above is based on the "ideal" 12 degrees posted earlier. If the primary seat were in the second row, then the theoretical 30 degree worst case could only happen for someone in the front row anyway. We could calculate the front row spacing based on my example if you would like, just for kicks!
 
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