Designing a ceiling for home cinema - projectorscreen, speakers, sound insulation, misc?

[Thorfun]

https://www.google.com/search?q=home+cinema+pelmet&tbm=isch&ved=2ahUKEwjW6LONjJbqAhWP0YUKHUWgD8cQ2-cCegQIABAA&oq=home+cinema+pelmet&gs_lcp=CgNpbWcQDFAAWABg8IgBaABwAHgAgAEAiAEAkgEAmAEAqgELZ3dzLXdpei1pbWc&sclient=img&ei=IP7wXtbYJI-jlwTFwL64DA&bih=1056&biw=1890&client=safari

[puntloos]

2 minutes ago, AliG said:

I was thinking of this kind of thing to hide the screen and possibly the ceiling speakers. We have something similar but our screen is fixed.

 

Actually our rear speakers are in the step, but the "above" Atmos speakers couldn't be that far to the edge so they are in the ceiling.

 

 

 

Ah! That makes a lot more sense. And such a ceiling has other benefits as well... (it could look quite pretty with lights installed).

 

Hm.

 

[Reiver]

You're right about not wanting the room too acoustically "dead", but looking at your pic, there wasn't much in the way of anything absorbent knocking about, hence my suggestion of the carpet. In a "normal" room, with some carpet on the floor, some furniture, some curtains and a few random humans there's generally enough to calm things down a bit, but I've been in some places which have gone for a very modern look where there's virtually nothing absorbent and they sound horrendous. One of the main things to avoid in my experience is hard, flat parallel surfaces as the sound will just bounce back and forth for a long time giving a nasty "flutter" echo in many cases. If you have the freedom to do so this can be sorted to some extent by angling walls (or the ceiling) to make the room non-rectangular or by making the walls non-flat.

Now on to isolation.

The best way to isolate sound is to build a "box within a box" structure, with no rigid ties between the inner and outer skins, only some absorbent stuff. Then the generated sound vibrates the inner skin, but that can't be coupled to the outer skin as they're separated, that's sort of the principle of the ceiling diagram you posted above where the plasterboard is resiliently mounted from the existing ceiling. This approach can be taken to ridiculous extremes as in one studio in London where IIRC they poured an inner box of reinforced concrete with 18" walls and a 12" concrete ceiling inside the existing building - all floating on an isolated floor. Coming down to a more practical domestic level the box-within-a-box can still be implemented, particularly if you're building from scratch. At it's most cost effective have 2 stud walls based on wotever x 100mm timber with slightly less than 600mm between the verticals, the 2 walls at least 75mm apart. Fill the gaps between the verticals with 600mm wide (hence the spacing) x 100mm thick mineral wool slabs of a reasonable density (like RW5 or 6), the outside surfaces get covered with double overlapped plasterboard - though I suspect cement bonded particle board  of a decent thickness will do just as well and might be easier to fix sometimes. Similarly for a suspended ceiling, beams THAT ARE ONLY MOUNTED TO THE INNER WALLS OF THE BOX with double plasterboard/CBPB underneath and mineral wool on top - then a gap and if you can stick some more mineral wool slabs in between the joists of the floor above (thin battens to keep it there) so much the better. Obviously the more mass you can put into the outer layer of the walls the better it will work, so if you can do one or both in high density brick or block it'll help, but you need to keep the mineral wool slabs and the air gap. If you wanted to go heavyweight on the ceiling it might mean smallish steel I beams to carry the weight I guess, but I'm not an SE.

Then there's the floor - it has to be solid or you'll have to make it part of the "box-within-a-box" Do all of the above on a suspended timber floor and you'll be wasting your time and your money. Done on a decent concrete slab it ought to be OK, though I've seen some perfectionists advise putting thin foam rubber strips under the outer boarding to isolate them from the floor, might be useful if the surface isn't uber flat..

Lastly you have to mind the gaps. It doesn't take much of a hole or a thin flimsy door to spoil things, likewise if you're going to be going loud and have NIMBY neighbours in close proximity, thick triple glazed windows will likely be needed.

Edited June 22, 2020 by Reiver

[Reiver]

Sorry just spotted a mistake line 13 should be 50mm apart