Film-Tech Forum ARCHIVE: Film-Tech Screening Room

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Posted by Andrew McCrea (Member # 674) on 01-06-2007, 07:57 PM:

Hey Brad,

I was looking at the warehouse picture of the FTSR and loved the step-by-step construction pictures.

I searched through the archives but couldn't find much on my specific questions.

I was looking at the booth floor construction, and realized (after talking to an architect recently) that they said a booth floor couldn't be made out of wood because the vibrations it would cause would be unacceptable. How did you avoid this in your screening room?

What are the dimensions of the projection booth?

Its a nice room; it must have cost a pretty penny!

Posted by James Westbrook (Member # 3690) on 01-07-2007, 03:33 PM:

The mall cinema I worked at until 94, the original twin side being built in 1972, had a booth floor of 3/4 inch plywood with floor tile on it.(Later it was carpeted with remnants.) The stairways leading up to these booths were also constructed of wood.
It can be done.

Posted by Tristan Lane (Member # 1169) on 01-07-2007, 05:24 PM:

I serviced a few theaters (now closed) that had wooden booth floors. I don't recall any vibration problems, but if you didn't step lightly when walking through the booth, you could actually cause the VIP pedestals to sway a little causing the image on screen to move.

I'm guessing that this problem wasn't strictly due to wood, but more likely due to poor support under the booth floor.

Posted by Brian Guckian (Member # 1678) on 01-07-2007, 05:42 PM:

I worked in a theatre where we had this issue, because the Projection Room had to have a sub-floor that could not place to much weight on the main slab beneath.

So an extremely rigid timber sub-structure was built, using very large cross-sections for the joists and placing these in two layers at right angles to each other, and in close proximity. I think they were only about 18 ins apart if I can remember (I was there when they were building it). On top of that, I think a double layer of thick ply was used for the floor, and then there were some thinner layers of floor covering (with anti-static vinyl on top).

The net result was an extremely solid floor with no movement. The important thing was that it was properly specified at design stage so the guys just built it as directed.

I have been in other projection rooms where the floor was too light and insufficiently-supported, as mentioned above. In fact there was a small chain of cinemas here who did that, so all their Projectionists were expert "tip-toers"!

Posted by Monte L Fullmer (Member # 2797) on 01-07-2007, 09:42 PM:

...like there were cheaply built 3 and 4 screen cinemas built in the mid 70's out of brick and plywood for less than $200k, thus they were named "plywood" palaces.

Even the booth floor was build with plywood flooring. The operators there would have to either work in stocking feet, or very light shoes, for the people down in the lobbies of these palaces can hear all of the footwork up in the booth, the 'humming' and 'whirring' of the machinery and other sounds down in the lobby.

Within a couple of years due to this design, the machines would start to list to the sides due to the weight on those weak floors. They had to be actually lifted up and steel plates had to be placed underneath to get the units back to level.

..It was just a disasterous construction plan in those days..and some of these plywood palaces were left vacant after a dozen years of operation.

Posted by Frank Angel (Member # 248) on 01-07-2007, 10:28 PM:

Sometimes even poured concrete doesn't guarantee a vibration-free base. Our booth is five floors up. When I was young and ambitious, I thought I might pull off an idea I had to move get them to approve installation of 70mm. To do this I thought, what's the point of going to 70mm if we couldn't get rid of that bad 5 story high angle. In my dreams I wanted a near Cinerama-style booth with a throw that was head on, screen-center. Problem was, the screen mid-point for 70mm projection would have been at the back of the mezzanine which was not possible because of a lobby that had entrances at the rear of the mezzanine. That left the balcony in which to build a 70mm booth.

During our exploritory investigation, we had an event booked into the theatre showed me something very scary: eventhough the balcony seemed to be about as structurally "solid" as one could imagine, it wasn't what it seemed.

We had The Beachboys booked into the theatre (back then they could still sing) and they required 5 follow spots for the show. This meant we had to add 3 extras SuperTroupers; they were setup in the balcony.

Imagine my surprise when we found that the entire balcony -- what we thought was a rock-solid foundation for those follow spots -- was shaking so much during the show that the spot images could actually be seen shaking on stage -- enough so it was very noticeable and very annoying to the group's stage manager. Seems that our balcony which was indeed poured concrete, was designed as a "floating" slab and when an audience is moving around, that movement created a shaking that was enough to cause the followspot images to shake on the stage, and more than likely, it would have the same ill effect on any 70mm projector images as well. Good thing we found this out before building a booth and installing projectors.

Then again, the smaller booth in the museum is built entirely in an existing room and everything is wood construction. It's rock-solid -- you can jump right next to the projector without incident. Go figure.

Posted by Andrew McCrea (Member # 674) on 01-08-2007, 12:24 AM:

Thanks for all the info!

I got a quote from an architect that concrete construction is about $125.00 per square foot. Does anyone know what that cost would be for wood?

Posted by Brad Miller (Member # 2) on 01-08-2007, 05:54 AM:

Extremely well braced wood for starters and a thick layer of insulation underneath it. I don't recall what the booth is. Something like 10x30ish. I should have made it bigger. It's cramped.

Go with stadium savers if you need to save money. It is essentially huge pieces of styrofoam cut to size and then a thin layer of concrete poured over it.

Posted by Gordon McLeod (Member # 33) on 01-08-2007, 08:16 AM:

Also check on firecode requriements as in many locations because of the electrical of rectifiers etc sitting on the floor it must be of noncombustable construction
I like steel Q deck on open web joists then filled with concrete as the base floor

Posted by Louis Bornwasser (Member # 3063) on 01-08-2007, 07:23 PM:

Have used wood beams under double plywood. Then covered with 1.5 inches of concrete. Remember the goal is to spread any weight or walking across as many beams as possible. If the crete is solid and not cracked, there should be little or no motion. The motion is a twisting motion. Louis