PE.T.R screen "live on your PC" development. - AVS Forum
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post #1 of 8 Old 10-10-2000, 06:20 AM - Thread Starter
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This thread is to design and critique the construction of a perforated acoustically transparent screen , that caters to The CINEMASCOPE aspect ratio first(in HDTV or dvd), HDTV aspect ratio second and 3/4 a distant third. In fact it prefers 2 3x4 images side by side so that to quote Apocalypse "YOU CAN EITHER SURF OR WATCH..."

Although the mold to produce such a screen will take into account the maximum envelope of the perforation device ( 60 x 141) with the support frame/bezel requirements, the maximum area of perforated viewing area 58.5 by 137.5.

My primary screen size however for the purposes of the design is 45 x 106 with perforated viewing area of 43.5 x 102.3.

Because I have specific plans for the inclusion of the second size screen as part of some condominium friendly system, please excuse me if I sound biased towards optimising to the smaller screen during the setting of design parameters.

For ceiling height 8 feet, for room lenght 18 to 22 for room width 13 to 16. The projector would be mounted in a soffit hush box that could vary (this is the dificult part)from 1.5 to 3. That means that the screen sold alone would need to have a hinge support to dial in the vertical ilumination. The pincushion trim of the screen would be designed to the 2.25 distance which is the middle point of 1.5 and 3.
The smaller screen's bottom distance to the floor is 48".

The larger screen would be an extension of the above screen as the same mold would be used.


By extrapolating interpolating the above ceiling height to lenght ratio an idea of possitionin in slightly larger/smaller rooms could be had.


WHAT ARE MY OPTIONS?

A sturdy , even surface is required, to prevent vibrations from the speakers behind. I know most of us have three channels only up front but I firmly believe in the 5 channel concept for 2.35 like in the Mann's Chinese theater, the academy theater, and SDDS. So a vertically flat but horisontally contoured (albeit slightly larger radius- to accomodate vertical tilting of the speakers down if the screen is slightly tited vertically up) speaker baffle (carpeted acoustical black withe the five vertical spk. cutouts) would have employed on the smaller screen scenario.

At this point it looks like a sealed box with 5 separate acoustical enclosures would be mounted and secured from behind the screen but toed down independent from the screens slightly upward inclination.

That leaves the question of the screen surface.

Plastic seems too fibble and may produce "digestive-like " sounds.

Aluminium velcroed against carpetted support would be ideal.

Peter M why is it so hard to form aluminum into the compound curve of no more than 10degrees?

Seems like the fiberglass kevlar option would work but i'd preffer aluminum.

All help is greatly appreciated.


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post #2 of 8 Old 10-10-2000, 10:00 AM - Thread Starter
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http://www.diamondfiberglass.com/covertanks.jpg

shows some silos made of fiberglass.

I could also visit a boat repair place.

Like:
http://www.diamondfiberglass.com/covertanks.jpg


ups just came to the door with perf metal samples. They are both way too open. They make a microperf look like a virgin.



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post #3 of 8 Old 10-10-2000, 05:21 PM
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Peter,

I would recommend you take some samples and place them in front of some speakers to see how they sound...I think you might be unpleasantly surprised. http://www.avsforum.com/ubb/frown.gif It may be that a lot of sound will be reflected (bad!) or absorbed and the attenuation may be too much to be dealt with just by re-equilization.

Oh, and I'm not the audiophile in the family, that would be my dad. http://www.avsforum.com/ubb/biggrin.gif I'm more the videophile, but I do try to be aware of issues that may affect the audio part of my home theater.

Regards,

Kam Fung
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post #4 of 8 Old 10-10-2000, 05:41 PM
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I have to agree with Kam here. I wish you the best but I do not see how fiberglass or aluminum will not severely hamper the soundfield. I think the WORST possible thing you can do to a speaker is to put a hard, reflective material in front of it. Good luck.
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post #5 of 8 Old 10-11-2000, 06:12 AM
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Peter,

You've got me a bit confused. What do you mean by "compound curve of no more than 10 degrees" ?

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post #6 of 8 Old 10-11-2000, 08:50 AM
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I think what Peter means, is that, if you lok at the curvature of the part of the screen that has the greatest 'rate of change' within the context of change/area, you end up with a change , from the beginning to the end of that area of greatest change, that has a variation of -starting point to finishing point of that area- no more than 10 degrees of total deflection from the starting point. Hopefully that is clear enough so that you do not have to read it mofe than a few times.

If you where to desccribe a sphere that encompassed the major characteristics of the curve section(meaning the screen proper), the sphere would easily be bigger than the room.

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post #7 of 8 Old 10-11-2000, 06:30 PM
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KBK,

What is the radius of the sphere ?

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post #8 of 8 Old 10-11-2000, 08:26 PM
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Well. You would think that it would encompass exactly that of the distance of the projector to the screen center. Which on average, would make the sphere bigger than the room.

There are ohther considerations when using CRT's though. You have to deal with the 'lens spread' and extrapolate how that woulld effect the curvature at the screen for a perfect focus. And design into the curvature a method of correcting it.


The adven tof single lens systems makes the discussion of such design considerations moot. There have to be considerations in looking at what happens when you take a lensing system that is designed to deal with a flat screen, and transpose that to a proper screen.

If they gave me aprojection system that worked as well as a CRT, then I wouldn't even go through the headache of dealing with the modifications to the curvature. The digital single lens systems, as i said, take almost all of the trouble out of such screens, as a design problem.


My comments as to differences within the curvature, and not exceeding, etc. apply only to the CRT desires within me. Perfect parabola, or surface sectioning is what will be needed with the DLP, DILA, and LCD screen.

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