Introduction

With the advent of DVDs and widescreen movie presentation, everyone seems to want to have a BIG picture. And, I don't mean just getting a 40" direct view. I am talking about 50", 60", and larger.

Flat panel plasma screens are available in 63", and probably by the end of 2004, maybe even 72" or 80". However, such plasmas are really expensive, upwards of $20,000. That is beyond the average consumer's budget.

Enter the front projector. A few years ago, when you wanted to consider a front projector, you were talking about a huge box with 9" CRTs. It gave a great image, nice and big, beautiful color. But, again, it was mucho dollars.

Digital projectors changed all that. The recent Sanyo Z2 review is a good example. For $2,000 you can put the projector on your coffee table and project it as big as you want. Let's say 72" wide. That ought to do it for most family rooms wouldn't you say? Or 60", or 120". Whatever you want. Just use the zoom lens.

And if you have not considered a front projector yet, well, consider it now, because, wow, what a difference a big picture makes when you have a big surround sound system.

OK, you might buy one, you say. But what about the screen? Where will you put it? If you get a big projection screen, it will block the speakers.

ClearPix

Several manufacturers make projection screens designed specifically to solve the problem of wanting a screen so large that it gets in the way of the speakers, namely, they are transparent to audio. They accomplish by using perforations in the screen. A problem sometimes occurs, however, with Moiré patterns being visible when watching movies. Comb filtering can also occur in the audio high frequencies with perforations.

Screen Research, a French company, has introduced a new product called ClearPix, which uses a material that apparently may have originated in the French fashion industry.

ClearPix screens come in all sizes and shapes (4:3, 16:9, and 2.35:1), but only in two gains: 0.95 white and 0.75 gray. The engineers at Screen Research decided to go with 0.95 gain instead of 1 or higher because they wanted the screen to be a uniform white with no hot-spotting. Today's digital projectors have higher brightness and better contrast than a few years ago, and since the material is very expensive, they decided to enter the market with a screen ideally suited to 3-chip DLP projectors.

The fabric is a woven fiberglass material, coated with vinyl. Here is a photo of the projection side of the screen, at a magnification that appears (on my monitor anyway) about what it actually looks like if you are viewing it from a normal computer monitor distance.

You can see the diagonal weave clearly. It is cut on the bias (diagonal) so that it can be hung without curling at the edges.

At an increased magnification, shown below, notice the detailed weave pattern

There is a small amount of space between the fibers, and this allows the sound to get through.

Now, because of the transparency, some of the light gets through as well, specifically about 10%. Most of us don't have black walls behind the screen, so this 10% can reflect off of the walls, not to mention other objects behind the screen if you use the motorized version. (If you mount the screen on the wall, the scrim is not necessary because you can simply paint the wall behind the screen flat black.)

To remedy this, ClearPix also supplies a black scrim material that can be ordered with the screen, and rolls down behind the screen on a weighted baton when it is lowered. Here is a photo of the scrim material.

The projection screen material currently is called CP-2. Sometime during the next year, CP-3 will be available, which is a lighter material that is easier to put into fixed frames, and should also be less expensive.

The Tests

I did not have a full sized screen for review, but the StJohn Group kindly sent me two samples, each about 1 meter square. One sample was the 0.95 white and the other was the black scrim.

Image-wise, the ClearPix was just a bit brighter than my reference Stewart Grayhawk screen (non-perforated). Like the Grayhawk, the ClearPix had essentially no falloff at side viewing angles, and no hot spots. But, the most important thing was, I could see no Moiré patterns.

At normal viewing distances, I could not see any weave pattern in the ClearPix, but up close, I could see it. Also, the pixels were diffused a little bit, compared to the smooth surface of the Grayhawk. This was expected, since the ClearPix surface is made up of tiny ridges due to individual vinyl fibers. This does not necessarily translate to any difference in resolution though.

I then tested the audio transparency.

For the test, I used a Thiel CS2.4 speaker. I did not want to filter the results using MLS techniques, so I placed a calibrated microphone just 3" from the Tweeter/Mid driver. I then used pink noise and collected a simple SPL response, with the total power set to 100 dB. After I collected the first response, with no screen material, I placed the ClearPix 0.95 white screen over the front of the speaker, equidistant in between the tweeter and the microphone, for the second response test, followed by a third response with both the screen and the black scrim.

Here are the results:

The red curve is with no screen material, blue is with just the white screen, and yellow is with both the screen and the black scrim. You can see that the curves are very close together. They are not flat curves because I had the microphone very close to the tweeter/mid driver and it was still picking up sounds from the woofer, which was farther away. But, what I was interested in here was how the curves changed with the screen.

The only noticeable differences were in the frequencies at 5 kHz and above. For example, at 5 kHz, you can see the red on top, the blue in the middle, and the yellow at the bottom, indicating several dB loss at that frequency. At about 14 kHz, however, the blue is on top, meaning that there was an increased response at that frequency with the screen. I think these variations are just due to having the sound filtered through a smaller number of fibers when the microphone was so close, and I suspect they would even out with the speakers being placed farther behind the screen and larger listening distances.

The main thing is that the response is still good even with the screen and black scrim in front of the speaker.  ClearPix seems to be wonderful stuff!

Overall, there was about 1.5 dB loss of total audio power through the screen and black scrim, which is what Screen Research states in their specifications.

Conclusions

I was pleasantly surprised at how well the ClearPix worked when it was placed in front of a speaker. It performs as advertised. If you are in the market for a top notch projection screen, and want to put your speakers behind it, definitely contact Screen Research (the StJohn Group in North America) and get the samples for yourself to try out. It is a great product!

- John E. Johnson, Jr. -

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