Pull Down Screen Wave Experiments - AVS Forum
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post #1 of 24 Old 06-09-2006, 11:14 AM - Thread Starter
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post #2 of 24 Old 06-10-2006, 06:26 PM
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Quote:
Originally Posted by tiddler View Post

I have been studying the photos of pull down screens with waves in them. The pattern of the waves suggests to me that applying some horizontal outward tension to the screen at the pull bar may fix the problem. Or the bar may have a very slight upward cure towards the ends. I would like to suggest a couple of experiments that could help to find a way to fix the waves. These experiments will probably require two people to perform.

The first experiment involves applying some horizontal tension about an inch above the pull bar. Each person stands beside the screen with one hand holding the end of the pull bar. With the other hand pinch the screen an inch or so above the bar. Both people gently pull the screen towards their end of the bar. If this reduces the waves then the solution would be to detach the screen material from the pull bar, pull it tight along the bar and reattach it.

The second experiment involves applying a curving force to the pull bar. Two people sit or kneel in front to the screen. They would each place the hand closest to the center of the screen under the bar. With their outer hands they grasp the bar as close to the ends as possible. Now gently push up with the center hands and pull down with the outer hands. If this reduces the waves then I think they were caused by the force of pulling the screen down from the center. The screen material may actually be stretched a little in the center or the bar may have developed a very slight upward curve towards the ends.

The idea of putting rebar in side the pull bar to add weight was suggested in a post. The seemed to be some success with that. I would speculate that concentrating the added weight towards the ends of the pull bar would be even more effective. I would even go so far as to suggest that manufacturers should be putting two handles on the pull bar or using a much stiffer pull bar.

I hope someone will perform these experiments and let us know what they find out. This potential wave problem has got me very wary of shelling out $1000 on a new screen.

There is a third thing you could try. As a matter of fact I would suggest you do this if one of the above experiments points to a solution. This will require three people to try. While one person very slowly puts the screen up. The other two stand on either side of the screen and gently apply outward tension on the screen near the roller as it is being retracted. I would suggest doing this a few times before drawing any conclusions about it's effect on the waves.

I'll show the photos to some of the mechanical engineers I work with and see if they have any other suggestions.

I'm no expert but the waves are probably caused by the roller size and the roller sagging in the middle. The Dalite Mod C is much better than the B model in the long run due to the 3" roller and more robust construction. Frankly, I do not think the pull bar has much bearing on the waves. It is probably more a characteristic of the fabric and the quality (size) of the roller.
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post #3 of 24 Old 06-10-2006, 06:41 PM
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Quote:
Originally Posted by hmcewin View Post

I'm no expert but the waves are probably caused by the roller size and the roller sagging in the middle. The Dalite Mod C is much better than the B model in the long run due to the 3" roller and more robust construction. Frankly, I do not think the pull bar has much bearing on the waves. It is probably more a characteristic of the fabric and the quality (size) of the roller.


Interesting comment. So how do you account for the waves in motorized screens? For example, some of the owners of Da-Lite's screens report waves in their screens, therefore if your premise is correct the rollers in these screens are undersized?
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post #4 of 24 Old 06-11-2006, 10:15 AM
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Both your comments are somewhat correct as there are a number of issues. As indicated, some roll-ups use a small diameter roller. Since the rollers are pinned at the ends (ie. end shaft / pins), they may tend to sag in the middle due to the inherent force pulling down on the screen. The waves will usually appears as "V". The larger the span the greater potential for sag problems and this is why the manufacturer usually specifies a larger roller for large spans.

Pulling down on the lower bar usually makes the problem worse as more force down results in more sag. This is why tensioned screens "pull out" and actually reduced the amount of force applied straight down because the tension cables basically remove the lower rail weight and "tie" it to each end of the roller (where they are "pinned") where it has less impact in causing sag. Manual pull downs may also have a related problem as result of constant pull down of the center draw to deploy the screen. This action may cause some stress on the roller but also stretches thin vinyl screen material. Fabric backed screens are probably less susceptible as the backing adds a bit of stiffness to the over screen to help distribute forces. Some of the "V" can also be overcome by fulling deploying the screen (ie. almost right to the end of the material on the roll) and insert a sheet of paper in the middle of the screen, then rerolling the sceen. The added thickness will help take up more screen material in the middle of the screen to help eliminated the "V".... from this you can tell that we are not talking about a lot of "play"... tolerances have to be "reasonably" close for waves not to happen.

Lastly, some people have "V" waves resulting from "poor" lower rail "grip".... that is, the material binding to the lower rail is not "stead fast" and as a result the material can slowly "gather" or shrink inwards resulting in a similar "V" situation. If the screen has this problem, then people usually try "unmaking" the lower rail binding or try "pulling out" screen (using two fingers run outward from the center along the lower rail) to try and stretch the material back out. The "pulling" sometimes help but usually they have to undo the "binding" and totally rework it.

Basically, I think the basic test for the problem is: if you have "V" waves, then undo (remove) your lower rail. If your waves are improved significant then it is likely that your screen can be helped by restretching the material on the lower rail. If they don't improve much, then it is likely a sag issue (or imperfect material mounting onto the roller... tough process) and you likely need to look at side tensioning. Finally, you have vertical waves, then you need to look at both your lower rail binding (better stretch of the material) and top roller (similar stretch.... but tougher to accomplish as the material is usually bonded on to the roller).
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post #5 of 24 Old 06-11-2006, 08:10 PM
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Stupid question, how do you remove the lower rail and will it reattach easily?

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post #6 of 24 Old 06-12-2006, 06:08 AM
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It depends on the make of the screen, some screens have the material wrapped around (or stapled to) a dowel which is then slid inside a metal tube with a slot on its full length. My Draper electric has a heavy metal extrusion that the screen is slid into... it has end caps that hold things in place (among other things - tab tension). If you look at your screen closely, you should be able to see how it accomplishes its "task". Ultimately, don't expect miracles from adjustments on non-tab tensioned screens as their cheaper design can only deliver so much.
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post #7 of 24 Old 06-12-2006, 11:46 AM
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hold it.... I didn't mean to scare you. As mentioned, "backed" screens have less problems, and as you have probably read here, HP due to its nature is better at "hiding" the waves during viewing..... so you are on the right track for your "money plans". However, if you are expecting a perfectly flat roll up screen at all times, both during viewing and "just hanging there" (in daylight / room light), you are probably going to be disappointed unless you go with some form of tab-tensioning. As stated, HP is probably the best option during viewing but will show waves in daylight / room light / non-viewing so if you can get by that, you will be OK. In general, you are right that waves are a scurge of roll up screens. Hence the vast number of posts on the issues.
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post #8 of 24 Old 06-12-2006, 03:51 PM
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There has been mention of manual tab screen.... Stewart if I recall.... which I think equates to $$$. I think the forum guys here have indicate the availability before. Yes your summary is good.
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post #9 of 24 Old 06-13-2006, 09:27 AM
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the problem is that dalite high power doesnt come in tab tensioned in an electric screeen, Dalite has said that you shouldnt get waves because the HP screen is their thickest material, dont know how true that is, maybe someone else with a dalite HP electric screen can comment
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post #10 of 24 Old 06-13-2006, 10:53 AM
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I have a 133" electric HP, it has waves but you don't see them when watching.

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post #11 of 24 Old 06-17-2006, 04:23 AM
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I also have a 133 HP model C. Ceiling mounted (10') and absolutely no gain loss issues or viewing cone troubles that so many on these boards seem to fret over. Sure the gain is higher if I get on a ladder to watch, but the PQ is great in my couch. There are waves but they are well hidden by the HP material. I do occasionally notice waves during slow pan scenes. For instance, recently I was watching a movie with a large cabinet in the background. As the camera moved past I noticed that the junk on top of the cabinet followed the wave in the screen. Noticing the waves, even if you obsessively look for them, is a rare occurrence.

I can't say enough for the screen. It is mated to an IF 4805 and everyone who comes over for friday movie night is absolutely blown away. There have been quite a few, "Damn I hope I can return that Plasma, DLP, LCD I just bought". I am also lined up to install 2 similar systems for friends that will cover all my investment thus far.
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post #12 of 24 Old 06-18-2006, 08:42 PM
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"Noah is your projector ceiling mounted?"

Yes, 7' high and 22' from the screen; I watchg from 13'.

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post #13 of 24 Old 06-22-2006, 07:08 PM
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Quote:
Originally Posted by budwich View Post

hold it.... I didn't mean to scare you. As mentioned, "backed" screens have less problems, and as you have probably read here, HP due to its nature is better at "hiding" the waves during viewing..... so you are on the right track for your "money plans". However, if you are expecting a perfectly flat roll up screen at all times, both during viewing and "just hanging there" (in daylight / room light), you are probably going to be disappointed unless you go with some form of tab-tensioning. As stated, HP is probably the best option during viewing but will show waves in daylight / room light / non-viewing so if you can get by that, you will be OK. In general, you are right that waves are a scurge of roll up screens. Hence the vast number of posts on the issues.

So what's the deal with the tab tensioned electric screens from elite? You can get a 100" screen from them for about $700.00. Are they total junk?

http://www.htmarket.com/tehc.html

Every other electric tab-tensioned screen is well over $1,000?

Also, are waves virtually eliminated with ALL tab tensioned screens?

Are waves worse with pull down than electric (non -tab tensioned screens)?
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post #14 of 24 Old 06-23-2006, 06:35 AM
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I doubt that they are "junk".... the difference probably falls in size of roller and overall operating costs (off-shore versus domestic). From the "stuff" that I have seen, basically offshore is ~50 cheaper even when you look at just plain electric roll ups.

I don't know if anyone has ever posted on the "tabbed elite". Can you ever have a "bad" tensioned screens????... probably but from my experience with Draper and the vinyl base of the material (very thin, light), I would say that the design leaves the screen basically flat like a sheet of paper.... there is some small waving in the black border areas where the tensioning is doing its "trick" but the viewing surface is flat.
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post #15 of 24 Old 06-23-2006, 07:29 AM
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Quote:
Originally Posted by budwich View Post

I doubt that they are "junk".... the difference probably falls in size of roller and overall operating costs (off-shore versus domestic). From the "stuff" that I have seen, basically offshore is ~50 cheaper even when you look at just plain electric roll ups.

I don't know if anyone has ever posted on the "tabbed elite". Can you ever have a "bad" tensioned screens????... probably but from my experience with Draper and the vinyl base of the material (very thin, light), I would say that the design leaves the screen basically flat like a sheet of paper.... there is some small waving in the black border areas where the tensioning is doing its "trick" but the viewing surface is flat.

I did more research and I do see that Elite is really Wuxi Cinon LTD (a Chinese mainlaind company).

Amazing how much less expensive their screens are with the chinese manufacturing.

If the quality is there -- it may bring down the prices on the better known brands.
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post #16 of 24 Old 06-25-2006, 07:23 AM
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Howdy gents.
I'm a newbie into this, so excuse me if I don't make much sense ;-)

I'm looking into constructing my own electric rolling screen, and trying to resolve the same issues you describe.
I intend to use the HCMW fabric, and construct a rolling mechanism made of a modified electric blinds motor.
It is not expensive (about $100) and comes constructed with a roller. The modification I want to make is to replace the 2" roller with a 4" roller. Since the motor is able to carry about 50 KG (~ 110 pound), I think it would be OK.

As for the expected V waves, I have an idea I haven't tested yet:
Instead of tab tensions, I intend to divide the lower bar to 3 areas Right, center and left. I'm not sure about the ratios yet, but something like 25%, 50%, 25%

My idea is to make the sidebars heavier than the center bar. With that I hope to minimize the tension on the center of the screen, and - hopefully - eliminate the "V" waves.
This is just a thought, but I'll be happy to hear your opinions about it...
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post #17 of 24 Old 06-25-2006, 02:55 PM
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"I want to make is to replace the 2" roller with a 4" roller. Since the motor is able to carry about 50 KG (~ 110 pound), I think it would be OK."

Double the roller diameter doubles the torque requirement, although it might not be an issue

The 50 kg I think would refer to the bearing load capacity.

"My idea is to make the sidebars heavier than the center bar. With that I hope to minimize the tension on the center of the screen, and - hopefully - eliminate the "V" waves."

Interesting idea, let us know how it works out.

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post #18 of 24 Old 07-01-2006, 10:00 PM
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"We each place a hand on the underside of the bar near the center. With the other hand we gently pulled down on the ends of the bar. By doing this we could eliminate the waves completely."

Most interesting. I'd have thought it would take some outward force at the sides.

If all that's needed is more downward force at the ends of the bar than the middle, the bar just needs to be fatter at the ends or skinnier in the middle.

If there's room in the loop that the bar slides into, maybe try wrapping some tape or thin foam around the bars at its ends.

Thanks for reporting your results.

Noah
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post #19 of 24 Old 07-02-2006, 12:29 PM
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If the roller had a reduced diameter at the ends beyond the image surface, there would be room for the cables and attachments.

It really doesn't seem that a DIY tensioned screen should be that hard (famous last words).

Just sew in the grommets, or an arced loop lined with a slippery material, and put in an elastic cable that's stretched by the weight of the bottom bar.

[edit] How about foam rollers at the ends so that as the edges w/cables roll up, they compress it.

I was thinking the edge material might get wrinkled and this would help, but maybe the compression would be worse.

Noah
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post #20 of 24 Old 07-19-2006, 12:46 AM
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I found a solution how to remove V-waves from the Da-Lite Deluxe 92'' (HCMW). Just put something between bottom bar and T-bar. This modification adds bending force (down force) to the bottom bar so that it reduces the V -waves from the fabric.
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post #21 of 24 Old 07-19-2006, 12:55 AM
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Quote:
Originally Posted by rado View Post

I found a solution how to remove V-waves from the Da-Lite Deluxe 92'' (HCMW). Just put something between bottom bar and T-bar. This modification adds bending force (down force) to the bottom bar so that it reduces the V -waves from the fabric.

Pictures of the operation are in the photo gallery under the Theater Construction...
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post #22 of 24 Old 02-19-2007, 02:33 PM
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Quote:
Originally Posted by funlvr1965 View Post

the problem is that dalite high power doesnt come in tab tensioned in an electric screeen, Dalite has said that you shouldnt get waves because the HP screen is their thickest material, dont know how true that is, maybe someone else with a dalite HP electric screen can comment

Newbie to this forum. Possibly reviving an old thread here

I have a Da-Lite cosmo electrol high power screen. I've had it for about 9 months or so now, and it's mostly in the down position. I might put it up 3 or 4 times per week.

It has waves, I'm sad to say.

However, the waves I'm seeing on my screen are more A-shaped than V-shaped. I liken it to the Atari symbol. It's really noticeable when watching hockey (yep, I'm Canadian - in Ottawa, like Tiddler). When the scene pans horizontally, the long lines of the boards show off the waves in a significant way. To the point where it's annoying me. And I'm not a purist by any stretch.

I use an Epson 550.

I just pinged my reseller, and he asked for pictures - so maybe there's something that can be done via Da-Lite. I'll report back once I know more.

I haven't experimented with any attempts at removing the waves yet. I do plan to, but I'm moving in a week, so there's other stuff on my plate at the moment. In the new place, I won't need to move it up and down, so I might try to fashion something to keep pressure in all directions to see if it helps. I've even thought of removing the material from the mechanism and building a fixed frame in which to mount the material. But that seems like a waste. It might be a tad too big for my new space. It's a 5' x 8' screen, with the remote control option. Again ... seems like a waste

Any ideas, please ping or pm me.

For anyone interested, I'll report back when I've heard from Da-Lite.
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post #23 of 24 Old 02-24-2007, 02:46 PM
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Maybe your lower rail / bar is bent up in the middle or your screen material was not mounted to your roller properly or has let go / stretch at the ends. Did you perhaps unroll it too much at some time.... this causes the glue to let go a bit. Always keep at least one complete roll of material on the roller. In terms, of a "quick fix", you can try unrolling as much of your screen as possible and then insert a sheet of paper (couple of sheets) on each end. Then roll the screen back up to its "normal" deployment. The "sheet thickness" will help take up more material on the ends and hopefully reduce your waves.
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post #24 of 24 Old 03-04-2007, 08:01 AM
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Interesting idea - thanks!

The more I looked at the waves, the more I realized they were pretty much vertical. The a-shape of it seemed more accidental than consistent.

I took a few pictures, and sent them to my retailer down in Toronto. He was great! His own expectations of this screen were that the material would hold up much better than it did. The pictures showed how pronounced the waves were. They were more so than I even realized. It was so gradual that I got conditionned to it. I've sinced moved, and am now projecting on the wall until I have everything settled. I'm actually appreciating the flatness of the wall now ... I realize how annoying those waves were!

We tried a few things to settle the material - similar to the ideas mentioned in this thread. But it didn't seem to help. My retailer will be able to provide some form of credit for the motorized frame, and provide me with a replacement (at some cost yet to be determined) permanent frame - which is more likely to perform well over time.

I don't have the final numbers yet, but I'm already extremely pleased with the attention provided by my retailer. I'm not sure whether or not it's allowed to mention him here, so I won't. If anyone is looking for a supplier in the southern Ontario region and is looking for a recommendation, PM me.

Cheers!
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