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I'm in the construction of a home cinema, and the plan is to make a 3-side (2 walls plus ceiling) wood frame construction that I'll line with fabric and fill with sound absorbing material.

Now I'm trying to estimate how thick wood I will need to carry the ceiling. Lo and behold my planning sketch:

enter image description here

The ceiling beams are 6x12 cm solid wood, the smallest ones that I could find in the length that I need (420 cm). They will carry some 2.4 by 4.8 cm cross bars above which I will place styrofoam as a sound absorber (not the best, but the lightest) and then close off the ceiling with fabric. One bar also will carry the projector, and there will be LED light strips and cables, etc.

I worry about the side frames (in light wood in this pic). How thick will they need to be to carry the ceiling construction? How can I calculate this at all? I have no clue about the strength of wood under various stresses. Should I make them more thick, just to be sure or am I worried for no reason?

Additional info:

  1. I want the entire construction to be free-standing, if possible. I would prefer to not drill into the walls or ceiling. But if you can explain me why that's a really stupid idea and I would make my life so much easier if I would hang it from the ceiling, let me know.

  2. In the pic, the side frames are made from 2.4 by 4.8 cm wood.

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  • Just an observation: I think sheets of styrofoam as a sound insulator will just be a waste of styrofoam. Extremely thick sheets, like the 2", might help some, but I doubt thin sheets will provide useful sound absorption. An alternative approach would be to use a suspended ceiling grid with acoustical tiles. If you want to stick with your concept, you would probably get better sound absorption with carpet padding or egg crate foam.
    – fixer1234
    Oct 9 '17 at 20:00
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How long are the 6 x 12cm beams?

With just two sides and a top you are going to have problems with a freestanding unit wanting to parallelogram unless you put some corner bracing in the upper corners that should span down at least 25 to 35% of the height. This of course can be mitigated by fastening into the existing building structure.

It is my feeling that the sides being framed from 2.4 x 4.8cm members is pretty flimsy. I would use something that is much sturdier more like on the order of 4.8 x 9.6cm for the side members.

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  • the top beams will be 420 cm long. They span the entire width of the room.
    – Tom
    Oct 9 '17 at 13:56

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