4-Way Acoustically Transparent Masking

I've just completed my front screen wall with 4-way DIY masking.

Over the next few days, I'll post pictures of the screen, followed by diagrams and pictures of the building process. Bear with me as I do this because I'm a bit slow at getting the diagrams drawn and pictures taken and then uploaded to the internet.

Here is my front wall without the wall panels...



Finished with masking at 16:9...



Finished with masking at 2.35:1 ...

I'm using a Panasonic AE1000 projector with a Prismasonic H-FE1500R anamorphic lens.

Here are some more pictures showing the masking.

Image size of 4:3



Image size of 16:9



Image size of 2.35:1



Image size of 2.40:1
(Notice that the top and bottom masking is moved in by a little bit compared to the picture above.)



(There is a bit of distortion in the above pictures because I am using a wide-angled lens on my camera. It is not there in real life. Also, I enhanced the photos by taking two identical images with the camera on a tripod. One is taken with the lights on and one with the lights off. I then superimposed the screen from the lights-out photo onto the lights-on photo. No other modifications were made to the images).





- Scott

Edited by ScottJ0007 - 1/1/13 at 8:32am

My masking system is probably more complicated than some of the others that have been described in this forum. I had a couple of special needs, that some of you may not have which means you can (and probably should) build a more simple solution.

My needs:
1) The masking material needed to be acoustically transparent. All of my speakers are behind an acoustically transparent SMX screen (127" wide). My speakers are moved to the very outside edges of the screen (In the very first photo in my first post, the speakers were closer together than where they are at now). When the masking moves from Cinemascope to 16:9, it covers the speakers.

2) On either side of my screen, I have doors that give access to the area behind my false wall. I wanted this access to remain clear of obstructions, therefore I could not use masking panels that slide back and forth on rails. Instead, I had to find a solution for my side masking that would fit in a space only a few inches wide.

3) Even though we talk about "constant height" I have found that I still need to make slight adjustments to the height of my screen for several reasons:

a) I have varying degrees of pin-cushion distortion with my lens set-up and I need to over-scan the image onto the masking more when I am in stretch mode than when I am in pass-through mode.

b) Any aspect ratio greater than 2.35:1 ends up being a little bit shorter in height compared to 2.35:1 unless you use the zoom feature on your projector. The exception would be if you have a scaler that will stretch in increments other than 1/3 (of course then you technically would need an anamorphic lens that would stretch in the same increment).

c) When I was building my screen and theater, I did not yet have the projector and lens. I wasn't exactly sure what height would eventually work in my room. I also wanted to future-proof my screen in case I ever get another projector or lens that has different throw characteristics.

Because of the above, I opted for four-way masking using rollers on the sides and using black GOM as the masking material.

Details will follow...

Here is a diagram of the side masking rollers and cables. This diagram is the top view, looking down on the assembly.
I will post some photos next.

Here are some detail pictures of side masking rollers and cables.
Everything was purchased at Home Depot except the fabric, the aluminum pipe, and the pipe bearings.







Patio door rollers mounted to strong-tie fittings found at Home Depot:


Spring and turn-buckle bolt



Note the back Gorilla masking tape. I had to use this because as the fabric rolls onto the pipe, the diameter gets bigger and the fabric begins to roll up faster. The cable has to roll onto the pipe at the same rate as the fabric or else it starts to bind. This is not an elegant solution, but it works. I wrapped several layers of tape where the cable starts on the pipe and then there are fewer and fewer as the cable wraps down the pipe, it was a trial and error effort that took some time to get right, but it works very smoothly now.

Here are some detail pictures of the bearing system I used for the vertical rollers. I can't stress how important it is to have the rollers operate smoothly. I had to completely scrap my first attempt because I tried to use electrical conduit pipe and PVC fittings for the vertical rollers. It was a miserable failure. This one works like a charm. I had to go to specialty suppliers to buy the aluminum pipe and the bearings.

That's it for the side masking. I'll post diagrams and pictures of the top and bottom horizontal masking later this week.

In case you are wondering... my masking system is not yet motorized. In all honesty it really doesn't need to be because it operates so easily and smoothly by hand. However, the COOL factor of a motorized system will probably entice me to add motors to it someday. It should be very easy to add motors to the roller bars.

As a side note... The masking probably cost me around $500 with all of the trial and error, including wasted materials and restarts. However, if you count the time I have spent, it has been ridiculously expensive. If I were starting over, I would probably look seriously at the HTIQ masking system. I met Don at CEDIA and saw his product and have also exchanged a few emails with him. His motorization system is exceptional, but I don't believe he has a four-way masking system with acoustically transparent fabric at this time.

Let me know if you have any questions about my masking system so far. I will do my best to answer.

The GOM fabric is attached to the aluminum pipe with Gorilla tape (from Home Depot). The only trick is making sure you get the fabric on straight. The gorilla tape is amaizingly strong. I also allowed for one extra wrap of fabric around the pipe, which means the fabric is always applying pressure to the top of the tape, even when the masking is fully extended.

To attach the cable, I used a short metal screw with a washer on it. I pre-drilled a hole for the screw and then screwed it into the pipe. The end of the cable goes under the washer. It holds great, plus allows for adjustment if needed.

I'll post some more pictures later this week. (I would go take a couple pictures now for you, but the theater is in use by my daughter and four of her friends ). In the mean time, there is about 1/4" to 1/2" between my screen and the horizontal masking. The horizontal masking itself about 1/2" thick. Then there is only about another 1/4" of space between the horizontal masking and the vertical masking shown above. I was careful to keep everything pretty tight to the screen because I didn't want to get any shadows.

Stef,
Here is a quick and dirty diagram showing the approximate distances from my memory. I'll confirm and take some photos as well...

Stef,
Here is a photo. It is kind of hard to take good pictures with the black background, but hopefully this gives you a good idea of the distances.

Now for the horizontal masking...

When I designed my horizontal masking, I didn't have any significant limitation for space above or below the screen so I decided to attach the masking to the back of the false wall. The concepts however can be modified if you want to use some of the ideas for a situation where you want the horizontal masking to be place in front of the screen.

I am finding that it is a little hard for me to describe my setup in words and two-dimensional diagrams, and the photos that I have tried to take are not as clear as I had hoped. (Photos of black on black are not easy).

The way I am going to try to do this is in steps. First, I need to explain how my screen is attached. I made my own screen frame out of 3/4" maple and intentionally did not put a boarder on the screen. Boarders add thickness to the screen but I wanted my masking to hug the screen as close as possible. Plus, my masking provides the boarder as seen in the pictures above.

The screen is attached to the back side of the false wall. I have two 1 X 4 pieces of board that span the distance of the screen opening. On the top board, I have an aluminum "U" channel attached to the bottom edge of the board. On the bottom board, I have an aluminum "J" channel attached to the top edge of the board. I made the "J" channel by taking a piece of "U" channel from Home Depot and simply cutting off part of the front "U" with a carbide saw blade on my table saw (be sure to wear EYE PROTECTION!). I install the screen by slipping it up into the "U" as far as it will go and the swinging the bottom of the screen into the "J", clearing the front edge of the "J". When the screen bottom hits the back of the "J", I drop it down. This setup makes it easy for me to remove the screen any time I need.

You can see the 1X4 boards and aluminum channel in the very first photo that I posted in this thread.

Here is a diagram...



I will post some photos later.

Horizontal Masking...

I know this diagram and the last one are pretty busy. Sorry about that but it is easier for me to explain it this way than trying to put it into words. After this I'll post some pictures...

The side masking simply stays where I put it. That is the beauty of the cable system. The cables put just enough tension on the vertical board to hold it perpendicular, but they do not pull it in either direction. Using about a pound of finger pressure, I just pull or push on the vertical board to slide it where I want it to go. (It will be very easy to motorize someday).

Here is my framing for my screen. It is 3/4" thick with no boarder.

These photos are of the upper left corner of the masking, from the front side:

with screen in place, side masking removed -


without screen in place, side masking removed -


-masking fully extended

These photos are of the upper left corner of the masking, from the BACK side:

with screen in place, side masking removed -

These photos are of the lower left corner of the masking, from the front side:

with screen in place, side masking removed -


the "U" channel for the cross bar is essential. Without it, the cross-bar tends to flop forward. It also guides it within 1/4" of the face of the screen.


-notice in this picture that there is a zip-tie wrapped tightly around the end of the cross piece of aluminum, inside of the aluminum "U" channel. This has two purposes, first it makes it more snug, and secondly, it helps the two pieces of metal slide easily and quietly.


with masking fully extended -

This photo is of the lower left corner of the masking, from the BACK side:

These photos are of the lower right corner of the masking, from the front side:

- masking fully extended
- also notice that there is no hem in the GOM fabric. A hem would stop the freying of the material, but it would also double the thickness on the edges and would cause problems when it rolls onto the roller bars. Instead, I used a product called "frey check". It is basically a fabric glue that I applied to all exposed edges of the GOM. It should never frey more than what you see in these pictures.