gedlee said:
What about some sort of loosely-woven flax or linen? If you have any decent bespoke shirtmakers in your area they may have an endbolt or two with which you could play.
The problem I often hear with loose woven mesh like fabrics, regardless of material, is the texture. In the case of natural fiber materials like you mentioned, the fabric has a texture and often a lot of stray fibers, which soften an image. The woven nylon materials, while having a texture, are woven in a way different from how natural fiber mesh is woven, and without any stray fibers.
Ebay is a great place to get end bolts, and I actually bought a few yards of a white cotton mesh material which looked similar to some of the acoustically transparent screen's I had seen, and was only a few dollars. I figured that cotton would have a minimum of loose fibers. However once I tested it I found it wasn't so acoustically transparent, and it had a very noticeable effect on softening the image. The material also suffered from an inability to be stretched without distorting the mesh badly. Which isn't to say your idea is completely without merit, I just didn't find the right kind.
But let's keep in mind that I wasn't trying to find an alternative to a bed sheet. Bed sheet's are very cheap, a king size 150 thread count sheet is around 5-10 dollars, and gives enough material for a 92" screen. The problem I had was if I wanted to go much bigger than that, I needed to find the raw material, and I wanted something with more gain. I also like the idea of a material that doesn't need to be stretched. I have had multiple screens now, most of which needed stretching, and even with tensioning systems, would develop wrinkles as the cloth stretched unevenly. I've never purchased an expensive screen, so maybe that is part of it, but Dr. Geddes seems happy with the bed sheet, and I've read many other people who also seem quite happy with the Bedsheet. In fact, I plan on using a black bed sheet behind whatever material I use, since it's basically the cheapest acoustically transparent material I've come across.
Ebay is a great place to get end bolts, and I actually bought a few yards of a white cotton mesh material which looked similar to some of the acoustically transparent screen's I had seen, and was only a few dollars. I figured that cotton would have a minimum of loose fibers. However once I tested it I found it wasn't so acoustically transparent, and it had a very noticeable effect on softening the image. The material also suffered from an inability to be stretched without distorting the mesh badly. Which isn't to say your idea is completely without merit, I just didn't find the right kind.
But let's keep in mind that I wasn't trying to find an alternative to a bed sheet. Bed sheet's are very cheap, a king size 150 thread count sheet is around 5-10 dollars, and gives enough material for a 92" screen. The problem I had was if I wanted to go much bigger than that, I needed to find the raw material, and I wanted something with more gain. I also like the idea of a material that doesn't need to be stretched. I have had multiple screens now, most of which needed stretching, and even with tensioning systems, would develop wrinkles as the cloth stretched unevenly. I've never purchased an expensive screen, so maybe that is part of it, but Dr. Geddes seems happy with the bed sheet, and I've read many other people who also seem quite happy with the Bedsheet. In fact, I plan on using a black bed sheet behind whatever material I use, since it's basically the cheapest acoustically transparent material I've come across.
Yeah I'm going to try your sheet method before anything else, no worries. You seem pretty confident in how good it is, it's the cheapest method, and you haven't steered me wrong yet.
I use 200 I think, but definately not 300, could be 150. The higher count will be better for video but worse for audio. It's a tradeoff that is up to you.
I've started a thread on avsforum for the GedLee speakers, and if any of you owners would care to contribute your impressions, we, the 'still shopping and learning' crowd, would appreciate hearing from you.
http://www.avsforum.com/avs-vb/showthread.php?t=1099840
http://www.avsforum.com/avs-vb/showthread.php?t=1099840
gedlee said:
http://www.diyaudio.com/forums/showthread.php?postid=1660116#post1660116
I'm not a screen expert but by looking at all the discussions surrounding color calibration (e.g. http://www.curtpalme.com/forum/viewtopic.php?t=10457) I feel that there are huge differences in screen material. Using a bed sheet is more like using a cheap speaker driver. It could work like expected but there's absolutely no guarantee.
Best, Markus
Markus
Yes, I think that other post is probably the incorrect one. I doubt that my screen is 300 count, but I don't remember. I've had "experts" here and asked them what screen they thought I was using. Nobody guessed right, one guy guessed Stewert. I am confident that what I use is fine.
From what I can tell about color calibration it's a lot like speaker wire. You can measure some effects but none of them seem to be important in the bigger picture unless they are very pronounced.
Yes, I think that other post is probably the incorrect one. I doubt that my screen is 300 count, but I don't remember. I've had "experts" here and asked them what screen they thought I was using. Nobody guessed right, one guy guessed Stewert. I am confident that what I use is fine.
From what I can tell about color calibration it's a lot like speaker wire. You can measure some effects but none of them seem to be important in the bigger picture unless they are very pronounced.
Matt,
Have you tried a phantom center channel?
If that works, perhaps you wouldn't need an AT screen and could get a "real" screen w/gain.
I'm a big fan of the Dalite Hipower.
Even if your projector isn't located for optimum gain, you still get the other benefits of its retroreflectivity - rejection of ambient light (except from the viewing direction, even illumination from any viewing position, and waves don't show.
I think a 110" pulldown is only $300; bigger than that and the prices jump.
Have you tried a phantom center channel?
If that works, perhaps you wouldn't need an AT screen and could get a "real" screen w/gain.
I'm a big fan of the Dalite Hipower.
Even if your projector isn't located for optimum gain, you still get the other benefits of its retroreflectivity - rejection of ambient light (except from the viewing direction, even illumination from any viewing position, and waves don't show.
I think a 110" pulldown is only $300; bigger than that and the prices jump.
I actually turned my screen into a retroreflective screen a few weeks back, and before that had simply attempted to make it into a high gain grey HC screen. I know a lot of people like the high power, I bought a sample piece to mimic my own off of. I bought retroreflective glass beads, which I believe to be the same thing they use, and added it to a paint blend which is in many ways a silver high gain retroreflective screen. The "silver" is really more of a grey with metallic powder added. This was sprayed onto my screen, and my measurements indicated roughly 2.5 gain, assuming my calibrated white card is still calibrated. I bought it off ebay, it was older, used, and I have no idea if it's still accurate. None the less, huge increase in gain.
The negatives of that screen, for me, are that it amplifies the blacks as well as the whites. I've compared with the Da-Lite, and it appears to be about the same, they both appear to amplify the blacks, causing them to look even more grey. It's fine with ambient light, but not great when I'm seriously watching during light controlled situations.
As for the phantom center, I've watched many a movie this way, it's ok, but I think I want a real center. For one thing, I spent the money to build one, I won't just not use it. I also think it's an important part of the movie sound standard, and exists for more than selling people more speakers. I do believe it adds to the movie, it's utilized to increase max output during loud portions of the movie, it locks dialogue to the characters, and it helps ensure a proper center image even when a lot is going on side to side. In other words, I want a center.
As for an acoustically transparent screen. Let's keep in mind, everything we have mentioned here are "real" screens. THX standards however dictate acoustically transparent screens, as do Thom Holman's own standard. They feel that to fully experience surround sound as it was meant to be experienced, the speakers need to be behind the screen. The only professional putting his name on products who doesn't support that view, that I know of, is Joe Khane, and is that really shocking, he isn't an audio guy, he's a video guy. I really think it's a mistake that we haven't done more to advance acoustically transparent screens more. I think non-AT screens are really unacceptable for serious theater, but good AT screens are few and far between.
Of course, this is my opinion based on what I value in a theater. Everyone has their own perspective, and just because THX supports it doesn't make it right. I know there are lot's of people who feel AT screens are unacceptable, causing unacceptable picture degradation and sound degradation. I mean, having seen the new JKP screens, I have no doubt that good 1080P projectors can seriously take advantage of smoother low gain screens for brilliant images, something no decent AT screen can achieve. Really only a white sheet fit's this category of smoothness, and even they aren't as smooth.
The negatives of that screen, for me, are that it amplifies the blacks as well as the whites. I've compared with the Da-Lite, and it appears to be about the same, they both appear to amplify the blacks, causing them to look even more grey. It's fine with ambient light, but not great when I'm seriously watching during light controlled situations.
As for the phantom center, I've watched many a movie this way, it's ok, but I think I want a real center. For one thing, I spent the money to build one, I won't just not use it. I also think it's an important part of the movie sound standard, and exists for more than selling people more speakers. I do believe it adds to the movie, it's utilized to increase max output during loud portions of the movie, it locks dialogue to the characters, and it helps ensure a proper center image even when a lot is going on side to side. In other words, I want a center.
As for an acoustically transparent screen. Let's keep in mind, everything we have mentioned here are "real" screens. THX standards however dictate acoustically transparent screens, as do Thom Holman's own standard. They feel that to fully experience surround sound as it was meant to be experienced, the speakers need to be behind the screen. The only professional putting his name on products who doesn't support that view, that I know of, is Joe Khane, and is that really shocking, he isn't an audio guy, he's a video guy. I really think it's a mistake that we haven't done more to advance acoustically transparent screens more. I think non-AT screens are really unacceptable for serious theater, but good AT screens are few and far between.
Of course, this is my opinion based on what I value in a theater. Everyone has their own perspective, and just because THX supports it doesn't make it right. I know there are lot's of people who feel AT screens are unacceptable, causing unacceptable picture degradation and sound degradation. I mean, having seen the new JKP screens, I have no doubt that good 1080P projectors can seriously take advantage of smoother low gain screens for brilliant images, something no decent AT screen can achieve. Really only a white sheet fit's this category of smoothness, and even they aren't as smooth.
well I don't want anyone reading this to think that I'm considering using a bed sheet because I'm being cheap or because I don't know better. I really do, it's just that Dr. Geddes seems to feel that it's the best compromise option for an AT screen with good picture, and it happens to be cheap too.
If the sheet isn't what I want, I'll try the screen from Seymour AV, and if that still doesn't work out, well, I always have this screen I'm using now, or I can try something else in the future. I have a sample of the Seymour AV screen coming that I will do some testing with. Screen Research hasn't gotten back to me, but another company who caries their line thinks they can get me a sample to try out.
If the sheet isn't what I want, I'll try the screen from Seymour AV, and if that still doesn't work out, well, I always have this screen I'm using now, or I can try something else in the future. I have a sample of the Seymour AV screen coming that I will do some testing with. Screen Research hasn't gotten back to me, but another company who caries their line thinks they can get me a sample to try out.
pjpoes said:
I really do hate when people equate price to performance. Just because its a bed sheet does not mean that it can't be the best for the application. Poeple get all hung up on price and "prestige".
If you look up my original waveguide paper in the AES journal you will see that the paper just following mine (I stumbled across this by accident a few yaers back) is by the research staff at some high class Japanese AV company who "discovered" a "woven fabric medium" had extremely good properties as a screen. I almost fell off my seat laughing when I read this, because all I could see was "BEDSHEET".
I would be out there ripping off people right and left with artificial BS about screens and speakers and everything else if I didn't find it so laughable. There is actually nothing impressive about ripping off a gullable public. Its convincing them to buy "the right thing" even if its cheap that is so difficult.
pjpoes said:
Interesting. Admittedly I have no recent experience with covered drivers (my only speakers with any sort of cloth over the fronts are my secondary subs) or projector screens (my TV is a 46" LCD) but I do wonder how much of that is the visual masquerading as the audible. Kind of like the "tube amps sound warmer" meme. (People see softly glowing incandescent light, thoughts immediately go to warmth!)
I would think that generally natural fibers breathe more than synthetics, which are all basically some form of petrochemical.
pjpoes said:
My experience with such fabrics consists only of having them made into shirts, but I can say that the better fresco-woven linens and linen-cotton blends, such as those by Riva, do not stretch at all. When I asked my old shirtmaker about that, he simply gave me a ~1m long, 25cm wide square of two (one all linen, one linen-cotton) and told me to measure it, hang it somewhere with a weight tied to one side, wait a month, measure again, and if I was content to come back and get measured for a couple shirts. I ended up coming back.
I also can't help but think that a great white shirting, such as one of Alumo's 140/2 Sea Island cottons, would look great in a room as a screen. Or maybe shorter fibers are better? (The typical individual fibers in a good 140/2 shirting are about 30-35mm in length, and very fine.) I know that such fabrics do better in Dr. Geddes' "blow test" than anything else I've seen or handled. I don't recall how wide such bolts are, though. They may be too narrow for a really big screen; I think the industry standard width is 1.5m, but that includes the selvage. And such fabric is far from cheap, alas, even if you buy an end bolt from a shirtmaker or a store that specializes in such things such as Tip Top in NYC...
Pallas said:
Its width that drives one to a bedsheet as no other application that I know of uses material that wide. And the bedsheet comes with a very nice ironed and pressed finish. I suspect that bolts of raw material will not have these features.
You know in many bed sheets that nice ironed and pressed finish is maintained as a result of starching. I would think that would cause problems with the acoustic transparency? I assumed you washed it and ironed it back out for the screen.
No absolutely not, I did not wash it - don't. That nice finish is what I want and my tests were all done with the starched sheet just as shipped. Perhaps you could gain a few tenths of a dB more acoustics, but washing the sheet will take out the finish that I wanted. I washed one once when I tried to dye it a grey color as I am a firm believer that screen "gain" is not at all what is wanted - blacker blacks is what I want and a grey screen helps this. The dye was not the color that I hoped and the nice finish was gone, so all-in-all this was not successful. I've not seen a bed sheet in the subtle grey that I am looking for.
Having gone the high gain route, I fully agree. I don't fully understand the infatuation with it. If that's what people want, they should be buying higher powered projectors, not HT projectors for light controlled rooms. Gain increases everything, including blacks, which I don't think is a good thing. The only advantage I hear is the rejection of stray light, but it comes at the expense of black levels and viewing angle.
Have you ever tried a grey sheet just to compare? My current screen is pretty dark grey, I think you could get away with it.
Did I read somewhere that a room acoustics thread was started? One that you are participating in? I'm really looking for some information on designing a relatively broad band resonant trap. There used to be websites that gave information on how to calculate such traps, but I can no longer find them. Idea's for making diffusers would be nice too.
Have you ever tried a grey sheet just to compare? My current screen is pretty dark grey, I think you could get away with it.
Did I read somewhere that a room acoustics thread was started? One that you are participating in? I'm really looking for some information on designing a relatively broad band resonant trap. There used to be websites that gave information on how to calculate such traps, but I can no longer find them. Idea's for making diffusers would be nice too.