The Placebo Effect - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 15 Old 01-13-10, 09:28 AM Thread Starter
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The Placebo Effect

pla•ce•bo (plə-sē'bō)
[Middle English, from Late Latin placēbō, I shall please (the first word of the first antiphon of the service), first person sing. future tense of Latin placēre, to please.]

noun: pl., -bos or -boes
  1. a. A substance containing no medication and prescribed or given to reinforce a patient's expectation to get well.
    b. An inactive substance or preparation used as a control in an experiment or test to determine the effectiveness of a medicinal drug.
  2. Something of no intrinsic remedial value that is used to appease or reassure another.
  3. Roman Catholic Church The service or office of vespers for the dead.

The definition refers mainly to medical use, however we all know it is a word used to describe anytime a perceived preconception elicits the brain to believe something even if it may not be happening. I did think the ‘vespers for the dead’ one was interesting…

Two quick analogies:

My dad was a mechanic and I used to help him work on cars and I would go to the parts store with him a lot. One day I asked the guy that owned the local parts store if Split Fire spark plugs really worked. He smiled and said “Ya know, when someone pays $8 for a single plug (that’s the price when they first came out), they tend to ‘think’ they are getting better gas mileage and performance. Personally I don’t see any difference in my car.”

The other one I ran into was the time I was in a high end audio/video store down in Virginia Beach. I was listening to two guys talk about their setups and they both had the exact same powered subwoofers, the only difference was one guy paid much more for his than the other guy. The man that spent a $150 more for the exact same make and model of subwoofer stood there arguing that his was better solely because he paid more for it.

It stands to reason that when a person makes something themselves there is a pride that goes into that effort. The same reasoning applies when someone spends a lot of money on something. Sometimes though, and just like the two analogies above, people convince themselves what they have is superior to anything out there, or anything anyone else could possibly build or think up. Subconsciously they want to believe they didn’t get ripped off or just wasted their time. Sometimes they may be right and they really did come up with something truly fantastic. Most of the time however human nature dictates that when a person puts a lot of hard work into something or spends a lot of money on an item or project… well you get my point. They don’t want to accept, let alone hear that just maybe after all their hard work what they have is something decent, but not necessarily earth shattering like they want it to be.

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken
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post #2 of 15 Old 01-13-10, 09:29 AM Thread Starter
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How does this relate to screens?

So what does all this mean and what am I getting at? I think there is a tremendous amount of work people put into their screen projects, and although the screen shots show some incredible images, I’ve also seen some pretty incredible images from the Do-able screens too, and the Wilsonart Designer screen shots look absolutely amazing. I’m not saying all techniques are bad or don’t work.

Yes some paints will give better performance than others, but is it possible, maybe even probable, that when someone spends a lot of time and money on something maybe they are seeing the performance of a Split Fire? I think anytime a person takes their time and does the right prep work and care to do something right, the results are always better than something rushed or done haphazardly due to inexperience or impatience. Once the experience level comes up, so does the quality of prep work as well as final results. I found that if you start with manure, and are using big bulky tools like say… bricks… you will end up with manure covered bricks and that’s pretty much it.

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken
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post #3 of 15 Old 01-13-10, 09:32 AM Thread Starter
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So is it the paint?

Partly- The biggest factors are whether the paint is neutral, and if it has a matte finish to it. That’s it, end of story. The last thing a person wants as a screen is a color and lots of sheen. So yes it can be said it’s the paint, but more important is what’s in the paint and what are the characteristics.

Interestingly though it has been proven that thinking this way, although seems to be logical and makes sense, isn’t always true. As was found with using a fine grain aluminum, in order to get a D65 neutral gray we needed a base that looks almost pinkish in color. So the comment made above by someone else doesn’t always hold true, but I believe his point was that if someone told him to add art glitter or neon colors to a mix he wouldn’t have to make up a batch to know it wouldn’t work. As long as it makes sense as far as colors and color science goes then it should work. Crazy ingredients or throwing things in just for the sake of adding them seldom really work.

Here’s what happens when most people start experimenting with screens and making their own mixes.

If your projector has a weakness like a low contrast ratio, then something that will boost the perceived contrast will be needed. How much of a boost is where the experimenting should take place and that would be with how dark or light of a gray you use. It may take several attempts to tweak the screen in for a specific projector. That however doesn’t mean the technique was bad, just some fine tuning was needed for that specific projector and of course personal preferences. The problem is that a constant color base must be used, and some people don’t do that. They jump around between mixes. If a person starts off with Silver Screen, then goes to a lamp black and white mixture, then tries something else, then a different mix… unless they happen to accidentally stumble on a D65 gray, what is happening is nothing more than guessing. It stands to reason that after awhile one of three things happens.
  1. As mentioned, the right neutral shade is stumbled upon purely by accident. The person may not see it that way though and will tend to convince themselves that it was hard work and their experimenting that yielded the results. They may even write volumes about their efforts and even convince others to use their method, which unfortunate when you break it down was just guessing.
  2. They get sick and tired of wasting time watching paint dry for countless hours and spending money on more paints to test and they just give up. When this happens pretty much whatever mix has a great screen shot along with what the current buzz is, ends up being is what the person tries. Since the technique is based on proper prep work and quality paint within the acceptable range for a screen color, the screen looks good, maybe even fantastic to them and they decide they found the holy grail of screens.
  3. They totally give up. Some people may just get so sick of trying this and trying that or all the flame wars that take place that whatever they have up becomes ‘acceptable’ and they are done. Even though in the back of their mind they know acceptable doesn’t mean optimal, they convince themselves once again they triumphed in the mystical world of DIY screens.

I’ll add an unofficial ‘4th’ item… when the wife steps in and says “NO MORE MONEY WILL BE SPENT ON PAINT” I guarantee there are some people that have spent hundreds of dollars on paint alone. That’s fine if this is a hobby and testing different colors is something you enjoy, but for most people they just want a screen and not a screen hobby.

This is why I stress that DIY needs a common standard, and that standard is a screen that is D65 neutral. Then a person doesn’t have to worry about color balance and other variables, just the shade of gray. Once the guess about grays is taken out of the equation, a person can then focus on determining whether they are a white screen person or a gray screen person, and if a gray screen, what Munsell rating. The reason they can do that is now they have a standard and know as long as things are proven to be D65 neutral they will all perform within certain parameters.

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken
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post #4 of 15 Old 01-13-10, 09:41 AM Thread Starter
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Mirrors

Do they work or is it just ‘smoke and mirrors’? The concept is very intriguing. A projected image hits a well prepared translucent coating on the mirror. Most of the light from the image is reflected back to the viewer in the form of a movie image. A small amount of light penetrates the coating, strikes the mirror and is reflected back through the paint. The reflected light won’t be strong enough to make it back to the viewer on its own, so what is theorized to happen is the translucent paint is vividly brighter in the bright areas while the blacks remain black. The effect theoretically should look like a backlit image. At least this is the original theory given as to why and how it works.

In theory, the light would take some time to penetrate the coating, strike the mirror, and then get reflected back through the coating. The first light strikes the screen surface and is reflected back to the viewer. In the time it takes for the light to make its way to the mirror and back the image is already changing, therefore the reflected light is ever so slightly out of phase with its original source. This could fill the pixel gaps with light, thus reducing the SDE, but that is all hypothetical now isn’t it?


Several questions come up, the first is does it work? Although I have never seen a full size mirrored screen in person, just some test panels made with smaller mirrors, the theory is ‘interesting’, and there are enough people around that have experimented with it and say yes… there is something there. How much and what it is can be hard to say. It stands to reason anything thought of on a public forum was already discussed and probably even beta tested by the big screen companies. That’s what they pay their engineers six figure plus incomes for… ideas and ways to improve things. I can’t say for certain that a commercial screen manufacturer has ever used a mirror for a screen, but I wouldn’t discount it and say they haven’t either. (Da-Lite does have a screen that uses aluminum, and aluminum is often used as a silver substitute as well as is used to make… ready? Mirrors! But it is a totally different concept than using a mirror as a substrate)

That brings up the next question, if they have tried it, then why isn’t it being sold to the jet setters and Hollywood elite as some exotic screen out of the price realm of mere mortals? Actually they probably could crank out a screen based on a mirror, charge $15,000 for it and say it’s the best on the planet and there would be people that would buy it... but does that make it better? If it truly is then I would think it would be on the market already.

It may give it an advantage, but personally I think most people have their HDTV’s and projected picture images over saturated as is, let alone pumping that up even higher. Where I think it would stand out the most is when there is more than normal ambient light in the viewing room. This does seem to make sense and appears to be a very good niche application for mirrored screens if they indeed work as theorized. One of the biggest problems I see though is it requires a very precise and thin layer of paint in order to get the claimed performance. Not everyone is up to the task of doing this. I even question if it can be done consistently without the aid of a robotic sprayer to get the exact thickness needed, which by the way has never actually been determined by anyone. It’s simply a hope and a prayer method and a lot of the good ole fashion placebo effect!

What we do know is anytime light passes through a medium of a different density it is refracted to some degree. If we go by the popular theory- by the time the light enters the surface paint it is refracted, then it travels through the paint, exits, where it is refracted again, is the reflected back causing it to re-enter the paint, therefore get refracted again... So it is an interesting concept, but in reality it just doesn't work... not like it is said to work at least, it doesn't turn a front projection system into a huge plasma screen as it is so often stated to do.

Should or does everyone need a mirrored screen even if they worked without a shadow of a doubt? No. Some people have requirements that dictate something that is durable as well as cleanable, maybe even scrub-able without degrading the screen image. Kids and animals could be a factor too. I think I would cry if I spent all that time and money on making an acrylic mirror based screen and a kid scratched it with something doing what kids do…

So it looks like a slight theoretical edge for mirrors, but cost wise and construction requirements probably take it out of the realm of half to three quarters of most DIYers. Hype wise almost everyone wants one whether they need it or not. Actual performance… the verdict is still out on that.

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken
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post #5 of 15 Old 01-13-10, 09:41 AM Thread Starter
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Name hype...

It was said before, what is a name? Names are picked for marketing reasons, you can be sure of that. Marketing, hype, and cost do not always equal the best though. As I said earlier, some people will pay more thinking it has to be better solely because it was more expensive. There is nothing you can say or do to change a person’s mind that thinks this way. But what about when money isn’t a factor? Take paint for instance. Behr has a high quality reputation, but is it really better than Glidden? Is that $2.00 savings you pocketed by going with Glidden going to cost you in screen performance? Honestly no… what is more important is whether it is neutral or a color. So why is Behr so popular? Specifically UPW and Silver Screen? Because of the name and all the people that talk about it. If hundreds or maybe even thousands of people use it then it must be good and it has to be the best solution available, right?

Wrong… People often go with the name most talked about, and in the DIY community maybe even more so than other markets. Sometimes large groups of people get together and comment on how wonderful something is that really doesn’t work as well as another product would. This doesn’t mean they are lying, rather it’s more of a case that it may look good and they just think the trade offs are normal no matter what is used. Or perhaps they have never seen a quality screen and compared to what they were using it really does look incredible, that is until they compare it to something that is better. Also some people are afraid to say “Hey you know what? That really didn’t work for me.” Saying that would make them an outcast. After all how could so many people be wrong? What works for one person may be totally wrong for someone else, that statement is a fact.

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken
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post #6 of 15 Old 01-13-10, 09:42 AM Thread Starter
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What works for one doesn’t always work for all…

On that note, don’t assume that just because something didn’t work for you that nobody else should use it either, unless there is some conclusive data or reason to show that it will have an affect on any projector that uses it as a screen. If that turns out to be the case, then it should be looked at as a person’s responsibility to the community to present their findings and facts to back it up. That way maybe something that started out as a decent but nowhere near perfect quick solution, and then was hyped to the max, can be weaned out of the list of viable options used for DIY screens. Also people need to keep in mind that what works for them doesn't mean it is what everyone should use... whether they like it or not! Some people are very aggressive at telling others what they 'like'.

So in closing, the entire point of this was to try to get people to stop and think for a minute before diving into something head first. Like the old saying “If something sounds too good to be true, it usually is,” Along with that should be; if something sounds just a bit too hyped to you, stop and take a good long look at it before spending your money. Also look at the data. No data and a lot of hype is usually a sign. If there is data, but still a lot of hype, tread carefully there too. Data can and sometimes is manipulated to support a desired conclusion. Read the data and test results carefully first before making a decision. Don’t take that placebo blindly and then convince yourself lips really are purple, or you spent hundreds of dollars on equipment so it HAS to be the best… even the Emperor was duped into walking through town naked, so make sure you read all the data and test results available and you’ll never get caught with your pants down!

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken

Last edited by wbassett; 01-13-10 at 01:04 PM.
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post #7 of 15 Old 01-13-10, 11:22 PM
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Re: The Placebo Effect

On the subject of mirrors...

Paint must be thick enough for its "true" colour to be seen. Pigments vary in their translucency. If we have a hypothetical case with three pigments each absorbing red blue or green (or their theoretical wavebands) and say, the green absorbing pigment is less efficient in its absorption, then "green" photons will penetrate further into the paint than "red' or "blue". If the paint is of sufficient thickness then this effect is mitigated by further interactions with green absorbing pigments. A neutral grey paint made from these pigments will be exactly the same colour for any thickness over a certain limit where the interactions between light and the substrate are effectively zero.

However the use of mirrors requires that the paint be thin enough so photons penetrate the paint and are reflected off the mirror. If due to variations in pigment translucence, some wavelengths penetrate better than others these wavelengths could be preferentially reflected causing a colour shift. The extent of this colour shift would be dependant on the film thickness. In order to get a neutral screen, pigments would need to be balanced for a precise thickness of paint.

A mirror screen with non-uniform film thickness could have local variations in spectral response (chroma-spotting?)
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post #8 of 15 Old 01-13-10, 11:46 PM Thread Starter
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Re: The Placebo Effect

You nailed it Rob.

There are a ton of variables, and each one can throw the entire balance off. But you have to admit... if you tell someone your screen is an 8'-10' diagonal mirror... well it sure sounds impressive and exotic whether it works or not.

"Make everything as simple as possible, but no simpler." - Albert Einstein

"If all else fails, spin the cat."- Grzboken
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post #9 of 15 Old 01-14-10, 12:28 AM
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Re: The Placebo Effect

Of course there is away to overcome the film thickness problem.

If the film thickness could be completely randomised on a very small scale then the overall effect would be the same as having a uniform film thickness because the average would win out when perceived by the eye.

To achieve this you could smash your mirror in a million small pieces and stir it into your paint. That way the fragments would become embedded at a variety of depths and the spectral response from any area would be uniform if measured on a sufficiently large scale.

The key would be on making the reflective particles small enough. Perhaps you could use fine metal flakes, something like aluminium perhaps?

Another advantage of this approach is there would be a variation in the orientation of the reflecting flakes. If they were not all orthoganal to the incident light they would reflect light slightly off axis and this would reduce any tendency to hotspot and lead to a wider viewing cone. Just an idea!
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post #10 of 15 Old 01-14-10, 06:46 AM
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Re: The Placebo Effect

Good one Rob! Why didn't we ever think of that.

Something else that needs to be taken into consideration when thinking about using a literal glass or acrylic mirror as a screen substrate is the separation, or "gap", between the front surface of the mirror (where the paint is applied) and the reflective backing. The usual thickness is about 1/8 of an inch. The light that does manage to get through the paint on the front surface of the mirror must then travel though that 1/8", be reflected and then travel back another 1/8" before it can again interact with the paint. Passing through this gap is not a free trip, but rather a toll-road. More light than you might think is absorbed by the glass/plastic itself, never to be seen again. When the reflected light does make it back to the rear of the paint layer it will tend to be reflected just as it was when it first struck the front of the paint layer so only a portion of the light will make it through back into the paint layer. It then must make it's way through the paint (a lot is absorbed into the paint at this point of it's journey as well) before it can finally break free and travel to your eye.

The primary promoters, at least that I am aware of, of mirror usage for screens have a whole convoluted theory of how light acts in this gap between the screen paint and the reflector, and while it can be a hoot to read it is very misinforming if taken seriously.

What using a mirror does is actually make a single substrate act as both a front-projection and a rear-projection screen at the same time. This is not a good thing if your goal is to create a sharply focused image. Back in the day when projectors were very low resolution, which resulted in large pixels; and had large gaps between the projected pixels (know as "screen door effect") a blurring of the image could actually be a good thing, but with todays high resolution PJ's and video media it no longer is.

Todays research into using reflective substrates for screens should be focused on the use of front-surface materials such as aluminized mylar.
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