CurtPalme.com Home Theater Forum

[mishaux]

Register to remove this ad. It's free!

I have read everything I can find on the forums about curved screens, but I haven't seen much about building a screen with a horizontal curve only. (as opposed to two axis curving like a torus)

I currently have a BD 808 and a 5x9 Wilsonart screen, but I am going to have to rebuild the screen and I was thinking about curving it to reduce the falloff around the edges.

Incidentally, if you dont want to have to rebuild your screen, don't use foam-compatible liquid nails to glue your laminate to 2" Styrofoam board. I put vertical lines of glue about every foot on the foam and pressed the laminate to it. Now I have vertical waves in my screen about a foot wide.

I would like to use MDF on my next try, but I soundproofed my theater room by hanging the sheetrock on metal track which hangs on rubber clamps which are mounted to the studs. This keeps vibration in the sheetrock from transferring to the studs to be radiated in to the next room. It also keeps me from mounting anything to the studs in the walls without defeating the soundprofing and possibly crushing the metal track behind the wall.

So I will be building the screen on legs to hold the weight, and I will only use the wall to help balance it.

That, and the fact that the falloff bothers me a little, got me thinking about curving the screen a little.

Something like this:



The amount of curvature in that mockup is probably way more than I would actually use, but it makes the point.

I would probably plan to use countersunk screws to attach MDF thin enough to be slightly flexible, but thick enough not to wave or sag, maybe 3/8", to the uprights. Then contact cement the laminate to that.

I don't want to limit viewing angle too much, but the room is no wider than the screen, so there isn't a wide viewing angle available.

I was thinking maybe a 6" difference from center to edge. Which is something like a 25' radius.

I don't want ruin the focus at the edges because the optics are built for a flat screen. I just want to try to spread the hotspot out a little.

I also expect this would make the hotspot in to more of a hot-vertical-bar that might shift some if you moved side to side.

Is there anything else I am forgetting? Has anyone tried this?

[Spanky Ham]

That sounds like a good plan. I don't think anyone has tried this. Maybe Dave did, but I can't remember if he did it or not. 6" should give you a nice image.

[garyfritz]

Search the avsforum archives and you can find a spreadsheet for calculating the curvature of a torus. You'd just need to use the horizontal curvature. Or you could just eyeball it and it'll probably work great.

[HogPilot]

[mishaux]

Thanks gentlemen,

The AVS stuff is great. I found the spreadsheet and it actually says the depth of the curve I want will be 5 and 15/16" Not bad for a blind guess. Wish my shade tree engineering was always that good.

I also saw somewhere that the HD145s are good for focusing up to 5-10% depth/width. Not sure how accurate that was, but 6" is just over 5%, so that looks good.

I did the HD145 mod with plates I made based on the Joust mod. I made a little change to his design that let me add adjustable schempflug to my BD 808. I keep meaning to post some pictures of that too. About time I started giving something back around here

I'll get some pictures of the screen up as I go.

Wish me luck!

[AnalogRocks]

luck!

[AnalogRocks]

luck!

[-Pjackso]

Just a note, the torus spreadsheet works best when the "Width of viewing area (L)" is set to 0.
By increasing the (L), the light concentration point (focal) is spread over a larger area - and hence the torus is less effective.
When (L) is set at 0 - it usually produces some large/deep curves, so some compromise is necessary.

...good luck.

[garyfritz]

Paul, doesn't setting the viewing area to 0 focus all the light at one spot, causing a dramatic dropoff of light as you move away from that spot? I thought the idea of setting the wider viewing area was to defocus the torus slightly so you have similar light levels across e.g. the width of your couch or seats. Width=0 may produce the highest light output at the sweet spot, but I'd think the consistency across the viewing area is more important.

[-Pjackso]

Gary,
You are absolutely correct, that was the point. The program spreads out the torus for a larger viewing area, at the compromise of less brightness. You understand the basis perfectly.

Unfortunately, I've always got the impression that people didn't fully understand the trade-off.
...for example, people thought that you could have the '0-focus' brightness - but now it could be over the entire area!
Or, people thought - well my couch is as wide as the screen, plug that in, ...wait a minute! - now the software says 0" torus depth! WTH?


So, without going into a full blown explanation of the trade-off's, I'd recommend going with 0-focus. When they see the 18" or 24" torus depth, they'll compromise by altering the width (and hence the torus depth). In the end, they'll have a bright torus screen (what they wanted) with close mathematical curves. The viewing area will be, ...well, whatever it works out to be.


I do think that if someone really thinks through the process, then the feature can be really useful. Unfortunately, when they DON'T fully understand it - then they end up building a torus that they're not happy with.


Who knows. Maybe I'm reading "between the lines" incorrectly.
In summary, yes - you understand things correctly.
For the people that don't fully understand it - I recommend to stay at 0-width or as close as you can stand it.

[mishaux]

Gentlemen,

Thanks for the input. I think I had the idea of what the worksheet was telling me. The spectrum goes from flat screen to fully focused torus, which makes the viewing go from a wide viewing angle compromised by falloff from any point, to full brightness without falloff from only one viewing point with major falloff from any other point.

My plan was to compromise between the two, and get a reasonable, but not complete reduction in falloff from anywhere on the couch. Which was what the viewing width thing was about.

I hope that is the idea, because I spent some hours on Saturday building it

I wanted a 5'x9' screen, but couldn't get MDF that big so I patched two sheets together. I decided to split the extra width I needed between both sides. It adds a seam to both sides which may or may not be visible, but at least they will be near the edge and symmetrical. I think that is better than a vertical seam two feet in on the left side only or something like that.





I cut and glued 4" wide strips of the MDF along the vertical seams and added some little blocks of scrap MDF along the horizontal seam in between where the 2x4s connect to try to keep the upper strip from curving differently than the lower. I am not sure it would have anyway, but better safe than sorry.



It doesn't look like the 2x4s are angled in the pictures, but they are turned a little to the tangent of the curve.

I wanted a "flatscreen TV" kind of look, so I kept the wide 2x8 base whole, but cut out the 2x8 cap so that it could go behind the screen.





I didnt want my inevitably sloppy jigsaw cut to affect the curve of the screen, so I cut it 3/8" too deep on purpose, so only the 2x4 uprights would be in contact with the MDF.





After I built the frame I used a countersink on the back board and screwed it to the frame. Contact cement and a good ab workout with a J roller and I was ready to call it a day.



The screen is perfectly smooth as far as I can tell. No ridges or seams or waves or bumps or anything. So that was a major victory.

It is heavy, but not that heavy. I got it up on those speakers by myself without destroying anything. Ill build a box for it to sit on with DVD shelves and a center channel built in at some point.

Next comes the black velvet boarder trim.

[Spanky Ham]

Nice job!

[ecrabb]

No kidding! Wow, I must have missed this.... Very cool.

Whenever you get a chance, when you get thing set up, I'd love to see a few screen shots of some flat color fields (light gray, red, blue, etc.)... I'd love to see what happens to the hot spot with the subtle curve. It's not bad on my Wilsonart screen, but it is noticeable in certain scenes when I go looking for it.

I'd also like to see/hear how the curve impacts edge focus.

Anyway... Kudos!

SC

[MikeEby]

[ecrabb]

[Sparky015]

Aother way to get the curve if you wanted to cut down the weight is to get rid of those studs and staple a few blocks on the top and bottom plates, cut kerfs into alightweight plywood/MDF, and then staple the kerfed plywood to the blocks on the plates. That will give you a perfectly smooth curve wihtout the weight of the studs. This is actually how furntiure makers make curved aprons and such

Interesting sign! Look forward to your results.

Paul

[mishaux]

Ok, it got cold out, so I am playing with my screen again.

Here is an update with the velvet surround.



It is 1x5 and 1x3 rectangular mdf trim (flexible enough to pin back against the curve without breaking, but ridged and light enough not to sag) wrapped in black velvet and set to just cover the edges of the formica.

And here is a 100 percent white screen to show hot spots and falloff.



The blue band 3/4 down the screen is a scan interference artifact from my camera.

There is just the faintest hint of colored hot spots from each tube, but the overall falloff has been reduced significantly. I used to be very aware of the falloff horizontally with a flat screen, I wish I had taken some pictures of it. Now I don't notice it at all. There is still faint falloff at the corners. I planned the curve to focus five feet behind the couch so that all the seats got a reasonably good view.

Edge focus is great. I have actually been able to get a better focus on the corners now then I did with a flat screen. Again, I wish I had taken pictures, the difference is fairly obvious.

Contrast is great. Maybe too great. I had never been able to see blooming before, but now with the blacks getting deeper I notice them with bright points on dark fields. Makes me want to upgrade to something with c elements

Next project will be velvet drapes on either side to help increase contrast even further.

Overall, I am extremely pleased. I still consistently marvel at what a fantastic display this all provides. Movie theaters now feel unwatchably dim and blurry to me in comparison.

[WanMan]

How about killing the room lights and posting some pictures of some test patterns?

[mishaux]

Sure,

Any in particular you are interested in? I have the HD Basics blu ray to work with.