From the Forums: DIY Fixed Acoustically-Transparent Projector Screen

Hide those front speakers away

by hodg100 May 24, 2017 at 2:38 PM

  • Some recent and quite extensive renovation work on Forums member Bert Coules’ bungalow gave him the opportunity to revamp the cinema area.
    Bert doesn’t consider it a cinema room because the ground floor is almost entirely open-plan. However part of the idea was to include a new screen and as he wanted to try putting the front speakers out of sight, it was decided that a complete false wall incorporating a five inch deep recess would be the solution.
    (Note the provision of a toilet for extremely long movies.)

    There used to be a window in this wall but Bert decided he could live without it (he has several others) and blocked it up. This solved some problems he'd had with the previous screen, including light bleeding through even though there was a blackout blind, and - more seriously - condensation.

    Bert decided to paint the walls and ceiling black, this time, rather than the previous darkish blue (though that was perfectly satisfactory) and discovered that matt black paint is pretty horrible to work with: it's difficult to get a decent uniform finish and once it's dry it shows up the lightest mark or blemish, so he might revert to blue (keeping the area behind the screen black to minimise any visibility through the fabric).

    The black paint made it tricky to get a good picture of the finished wall with the speakers in place, so he’s lightened this one to make things a bit clearer:
    The two lower speakers are for a separate stereo installation. The cinema speakers are nearer the top of the recess than Bert would like (a miscalculation of exactly how high the screen would have to hang) and the placing does colour the sound very slightly, but he got used to it very quickly and doesn't notice it now.

    Back to the screen itself, Bert neglected to take a picture of the bare frame but you can get the idea from this image of a bit later in the build:
    It's a straightforward assembly of 65 x 20mm planed timber, screwed and glued with added T plates and corner pieces for good luck. Overall size is 109 x 44 ins or 2770 x 1120mm if you prefer. The front face of the frame is painted matt black, sanded down between coats and after the final one, in order to give a smooth surface which won't snag the screen material when it's stretched. The rectangular plate in the centre of one long edge (the top of the screen) locates on a similar construction on the wall and has (so far) proved to be the only fixing needed to hold the screen in place.

    Bert decided to try Filmex for the screen material and ordered some from Epic Home Cinema. Two layers are recommended and he was pleased to find that the order arrived already cut into two pieces. Here's the first layer just loosely laid on the frame:
    You can see that there was ample width to play with. The fact that the material wasn't as long as the frame was no problem: it's extremely stretchy. Bert fixed first the centres of the four edges then worked outwards towards the corners, stapling every inch or so and working in six-inch increments: one long edge then the opposite, then the short edges. It took a while to get the degree of stretching right - he was too timid to begin with - but he quickly got the feel for it.
    Mostly, Bert pulled the Filmex around to the back of the frame and stapled it there, but had to fix the short edges to the sides of the frame at first, because of the way it was being supported. More staples were added, on the back, once the whole assembly had been turned and trimmed of excess material:
    With it flipped over again Bert started on the second layer:
    ...and followed exactly the same procedure. After trimming off the excess he taped down the cut edges of the Filmex:.
    ...though the tape is hard to see in the picture. He used self-adhesive plasterboard jointing scrim, purely because he had some handy, but it wasn't a good choice: it hasn't stuck well to the fabric and will have to be replaced with something better, possibly the specialist tape used for the back of artists' canvasses and picture frames. Bert also suspects that conventional duct or parcel tape would also not be very good.

    Here's the screen in place, still lacking its 2.35:1 border and whatever masking he decides on to get it down to 16:9 and (ideally) 4:3:
    Bert says he’s very pleased with the Filmex, which gives a splendid image with no moiré patterning and nothing visible through it (he was slightly concerned about the high-gloss finish on the speakers possibly catching the light and reflecting it back, but it doesn't) and the effect of having the sound come from behind the screen is pleasing too, if not as great a difference from the old speaker placing on top of the units as he was perhaps expecting. As far as Bert can tell, the double layer of Filmex doesn't have any effect on the sound at all.

    Good Job, Bert, very Coules!

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