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post #1 of 30 Old 02-25-2007, 09:15 PM - Thread Starter
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If a front projector is put in a seperate room behind the main theater room and projects through a piece of glass (plastic?) to the screen, is any type of special glass needed or desired?

Would insulated (dual layer) glass work in an effort to keep projector room noise from entering the theater?

Thanks!
Scott
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post #2 of 30 Old 02-26-2007, 12:46 AM
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Use only a single sheet of AR coated optical grade glass - don't use plastic, dual layer glass or similar or it will decrease image quality.

Mike

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post #3 of 30 Old 02-26-2007, 04:25 AM
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And make sure that the light from the PJ does not enter the glass at an angle.

Tboy
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post #4 of 30 Old 02-26-2007, 04:41 AM
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Quote:
Originally Posted by Tboy555 View Post

And make sure that the light from the PJ does not enter the glass at an angle.

Tboy

Standard "porthole" design in professional theaters is to use two sheets of glass for sound isolation. In this case, you do want to angle the glass to avoid internal light reflections.

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post #5 of 30 Old 02-26-2007, 03:24 PM - Thread Starter
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How would you angle the glass in this case to avoid reflections?

Thanks
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post #6 of 30 Old 02-26-2007, 04:54 PM
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Quote:
Originally Posted by SES View Post

How would you angle the glass in this case to avoid reflections?

Angles in commercial movie theaters may range from about 5 degrees to 15 degrees of tilt.

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post #7 of 30 Old 02-26-2007, 06:05 PM
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For those looking for a locally available solution, Plexiglas G (and only the "G") is water clear and works quite well, except for the fact that it is not optically coated. It is relatively soft and can be scratched, so always use a plexiglass cleaner on it. The surfaces are optically flat and will not cause any distortion in the screen image like you would find with Lexan.

Finding optically coated water clear glass in most cities is just about impossible without special ordering it. Finding optically coated water clear glass in a large sheet, 12" x 48" for example, is even more difficult.

Vern
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post #8 of 30 Old 02-26-2007, 06:15 PM
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You can try Edmund Scientific in NJ as a source. That's where I got mine.

Regards,
Doc
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post #9 of 30 Old 10-18-2007, 04:31 PM
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I am about to reach the point of installing a glass window between the projector room and the theater room for the HT room I am building.

I have put a lot of work in on soundproofing, so I am inclined to go with the two panes of glass. Given I plan to use an RS1 intially (700 lumens) is there any light loss for using two panes over one?

I see the recommendation for angling the two glass panes. Could someone explain this recommendation - why is an angle needed/desirable? Is the idea one is vertical, and the other is angled as 5-15 degrees? How do you select the angle to be used?

Finally, where does one find a supplier of anti-reflective coated glass in Toronto ON Canada or that will ship there? My window is around 23"x14"

Thanks for any assistance.

Eric

PS I checked Edmund's web site, but saw nothing like this. Who do you talk to there?
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post #10 of 30 Old 10-18-2007, 05:01 PM
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http://www.edmundoptics.com/onlineca...productid=1919
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post #11 of 30 Old 10-18-2007, 06:12 PM
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oh, Edmund Optics. Thanks, that is helpful.

Do you know if they handle sizes larger than the web page listed 10x12?
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post #12 of 30 Old 10-18-2007, 06:18 PM
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got mine from edmund optics. fast shipping, good product! as far as angle, when i worked as a part time projectionst, the window was angled about 10 degrees down as well as being coated. a large projection port just sold on ebay for around $25, easily worth more. i missed out on it though. worth it to keep watch.

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post #13 of 30 Old 10-18-2007, 06:20 PM
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Why such a large piece? In my last theater I used small 3" square piece just in front of the lens.
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post #14 of 30 Old 10-18-2007, 06:22 PM
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Well, there is an anamorphic lens between the pj and a large screen not that far away... and some extra room...
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post #15 of 30 Old 10-18-2007, 06:27 PM
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Quote:
Originally Posted by Eric Carroll View Post

I have put a lot of work in on soundproofing, so I am inclined to go with the two panes of glass. Given I plan to use an RS1 intially (700 lumens) is there any light loss for using two panes over one?

I see the recommendation for angling the two glass panes. Could someone explain this recommendation - why is an angle needed/desirable? Is the idea one is vertical, and the other is angled as 5-15 degrees? How do you select the angle to be used?

There will always be some light loss through glass, and using two panes over one for sound isolation will increase that loss, but if you use clean optical quality glass with anti-reflection coatings, the light loss will be extremely minimal (only measurable using a light meter, not your eyes). Port glass should never be installed perpendicular to the projection beam to avoid light reflection back to the projector lens (even using anti-reflection treated optical glass). If two panes are used, care should be taken to avoid internal re-reflection by angling the two panes. A general recommendation is a 7 degree outward tilt from the perpendicular plane of the projector on the projector side pane. The second pane port glass angled up slightly on the theater side avoids light from the screen being reflected to the audience.

23x14 is a huge window size, most projector ports are around 6". Optical glass is not cheap, you may want to look at minimizing this window.

"Me, I watch movies in my screening room...If you go to a movie theater today, everybody talks about candy, popcorn, where they want to eat later. Never the movie. It's rude."
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post #16 of 30 Old 10-18-2007, 06:30 PM
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oooh, that will do it

Here's a link that might also help:
http://www.rsem.com/equipment-list.asp?category=porthole%20windows&subcategory=porthole%20glass

On the left side of the site look under "porthole windows" for more.
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post #17 of 30 Old 10-18-2007, 06:52 PM
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Thanks very much for the window port reference, and explanation, that's just what I was looking for.

To put some numbers to "how far"...

I am using a 127" W x 54" H 2.35:1 screen in a CIH configuration. The wall the pj is firing through is 14.5" thick (soundproof with built in acoustic treatment). Distance from anamorphic lens to screen is about 234" and PJ is another 7" back from that. So total distance to screen is 241" or about 20'.

I suspect the smallest finished opening I could use would be around 17" W x 10" H. It might be possible to go a bit smaller but that is tight as it is, I think its like 1-2" clearance on the beam.

I think I misread the plan, and the finished opening is currently expected to be 21" W x 12.4" H. I think the 23" W x 14" H is the unfinished opening.
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post #18 of 30 Old 10-18-2007, 07:38 PM
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Quote:
Originally Posted by Zinema View Post

Use only a single sheet of AR coated optical grade glass - don't use plastic, dual layer glass or similar or it will decrease image quality.

Zinema,

What's the concern about double panes of glass? THis is pretty important for soundproofing...

Eric
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post #19 of 30 Old 10-18-2007, 07:59 PM
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I used Edmunds "Float" glass and mounted the 5"x7" piece into a custom frame that I made and attached it with Velcro so that I could remove it and clean it when dust eventually gets onto it. Works fine.

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post #20 of 30 Old 10-19-2007, 04:24 AM
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I ran out of time (and energy) before my meet at the end of last month and the new set up is so much more quiet than my CRT system anyway but here is my port. I bought glass from Edmund per the recommendations of folks here on the forum. I believe the easiest thing is to angle the glass and mount it on the projector side of the opening. A custom frame can be built thus eliminating the need to cut the glass as well as allowing a much smaller piece.







Art

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post #21 of 30 Old 10-19-2007, 06:05 AM
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Quote:
Originally Posted by Eric Carroll View Post

...
Is the idea one is vertical, and the other is angled as 5-15 degrees? How do you select the angle to be used?

Anything in that range should be just fine. The idea is that a shallow angle prevents reflection back and forth between two panes of glass, but is not so steep as to create extra glass for the projector beam to go through, and thereby be needlessly attenuated.

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post #22 of 30 Old 10-19-2007, 02:54 PM
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Quote:
Originally Posted by Andy238 View Post

Here's a link that might also help:
http://www.rsem.com/equipment-list.a...rthole%20glass

I also found Kelmar.

Does anyone have any experience with R. S. Engineering's models? I was thinking the Goldberg Brothers 18x18 angled double pane with AR glass might be a good fit to my requirements (have to look at the beam size again).

Any other manufacturer recommendations or does everyone just DIY?

Eric
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post #23 of 30 Old 10-19-2007, 02:57 PM
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Art,

I love the blackout pieces to the side of the lens. Is this just decorative or is there a rationale for it?

What is it made from? MDF?

Eric
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post #24 of 30 Old 10-19-2007, 03:10 PM
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Quote:
Originally Posted by Eric Carroll View Post

The wall the pj is firing through is 14.5" thick (soundproof with built in acoustic treatment).

I think I figured out the problem. I think I am overspecifying the beam size due to the perception of the wall depth. The wall is actually a compound wall: built in acoustic treatment trap and the actual soundproof wall. The treatment section needs to be open to pass the beam, but is not involved in supporting the port. Just the soundproof wall itself is likely 7" deep (need to confirm this). So I need to relook at the beam size 7" off the anamorphic lens to see what size port I really need. Hopefully its much smaller than I have been calculating in this thread, which should open up my choices substantially.

Of course the "soft" part of the wall (the trap section) will have to stay clear of the beam through the balance of its depth...

Eric
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post #25 of 30 Old 10-19-2007, 03:36 PM
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Quote:
Originally Posted by Eric Carroll View Post

Art,

I love the blackout pieces to the side of the lens. Is this just decorative or is there a rationale for it?

What is it made from? MDF?

Eric

Thanks Eric ! We weren't sure about the size and design of the port so we made it large enough to be sure it would work regardless of the final projector position. The blocks fill the space left to reduce light and fan noise out of the projection room. Additionally ,they added a nice esthetic touch.Yes ,they are MDF covered with velvet friction fitted into the spece.

Art

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post #26 of 30 Old 10-19-2007, 09:56 PM
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Well well.

Recalulating for a 6" projector depth, 7" lens and 7" wall suggests my projector port needs to be a minimum of 11.2" W x 4.76" H. So a 10x12 piece of glass would do the trick. Or the Goldberg 18x18 double pane angled, gasketed porthole would work well too (a bit oversized).
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post #27 of 30 Old 10-20-2007, 09:12 AM
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post #28 of 30 Old 10-20-2007, 11:17 AM
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Quote:
Originally Posted by mvesledahl View Post

Here's another option...

http://www.acousticalsurfaces.com/ac...tudio.htm?d=40

Thanks for this reference, it looks like a good solution. I will give them a call to see about pricing.
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post #29 of 30 Old 10-22-2007, 03:27 PM
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This looks like the option I will go with.

It is an amazing 1" thick, based on two 1/8" panes laminiated together, 1/2" air gap, and another two panes of laminated 1/8" glass, in a angled 1" thick openable frame. They also provide an glass upgrade option for Optiwhite Glass. STC rating is 49.

The finished port hole size of 18W x 17H in the 20x20 unit is "just right".

Eric
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post #30 of 30 Old 10-06-2013, 07:03 AM
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Finally got around to putting in an optical glass port . My Display Design HD5 is significantly louder than than my HT5000 so I felt it was needed. One pane of 5x7 Edmund AR coated glass did the trick. This cut down the fan noise coming into the theater by approximately 80%. The glass is quite thin at 1mm.



I built a frame then tweeked it a bit to get the image right in the middle of the glass area. It has an 8 degree tilt, although I guess this is only needed if you are using two panes.It is friction fitted with a felt edge so If it degraded the image I could easily remove it to modify if I wanted

Next I need to deal with the sound coming through the rack since now I can hear that.biggrin.gif

Art

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