Possible idea for 8' truss cieling

RyanC · Post by **RyanC** » Tue Jul 26, 2005 5:10 pm

I have a room with 8' cielings and I am looking for ways to expand at least part of it higher in the main room. It's a truss cieling so cathedraling would be too difficult- and it is only about a 5' rise at the peak so it would be a fiarly obtuse angle anyway.

The joists are on 24" centers and I was looking at a skylight the other day and thinking about somthing like that between the joists- but with no window.

It would not be too difficult to build up ?' x 2' boxes with tops that were slated at various angles, rip out the drywall and insert the boxes between the joists. MDF maybe-

Of course the boxes could all be different depths too making a larger random diffuser/non-parrallel reflector-

My main concern is that if the boxes were parrallel in the direction of the trusses would I be making the room sound worse? The sound would not origionate in the parrallel space, and a mic would not be in there either (unless. . . ) The other thought would be to make some 4' wide that slanted over 1 joist, but this would be more difficult.

any thoughts are appriciated-

knightfly · Post by **knightfly** » Sat Jul 30, 2005 5:33 am

Diffusors with deep and wide wells such as this need really long distances from ears/mics to work; otherwise there are too many focussed, specular reflections (makes things sound worse :=) - also, as you apparently already know, removing trusses from an already built house isn't something to be taken lightly - depending on spans involved, etc, it would likely be dangerous if done wrong. I don't think I'd mess with it at all. Instead probably just do some "clouds" of 2-3" rockwool, spaced 2-3" off the ceiling... Steve

RyanC · Post by **RyanC** » Sat Jul 30, 2005 11:46 am

Interesting-

What if the boxes were pyramid shaped- EG all non parrallel with the floor. I already have some clouds and they work pretty well- but I am considering floating the floor and if I lost inches on the floor then it would start to feel too closed in.

Anyway it makes sense to me what your are saying strictly as a diffuser standpoint, but it seems if they were long (say 10') and sloping angles they wouldn't really act as diffuser wells so much as non parrallel cieling surfaces? Providing a more diffused sound field (or at least a non ringy one), but not an acutal QRD or the like. Especially as the "well" depth is inconsistant (slanted). I want the room to be live- but also not excesivly ringy.

So say 8-12' long x 2' wide slanted on the top so as to provide a non-parrallel reflective surface to the floor. The fundamental mode of the 2' parrallel surface would be about 550 hz so some foam or fabric should be able to attenuate the side to side reflections sufficiently, no?

I just want to make sure that we are on the same page- if its a bad idea that's fine- but I think you are thinking square wells that have parrallel tops which is not what I have in mind.

Oh and I have plenty of construction experience, plus a firend who is a structural engineer and another friend who builds skyscrapers and stadiums (literally) so trust me I won't go and do anything stupid like ripping out the trusses- unless I was going to reframe the whole roof, in which case I would seek appropriate help.

knightfly · Post by **knightfly** » Wed Aug 03, 2005 3:20 am

Pyramid shaped cavities will "focus" sound at different spots in the room; probably even worse idea than square 2' wide wells, which would have a working distance (as a diffusor) of several YARDS - any closer and you'd have no chance for diffusion to "kick in"... Steve