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Spray-in insulation and acoustic absorption

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Brian Jojade:
The spray foam should help prevent the metal structure from rattling with sound. However, as others have said, you're replacing one hard surface with another.  While the irregularities will potentially redirect some of the higher frequencies, it's not going to absorb much at all.  And if you cover it with another material, it isn't going to have that much impact in the sound within the room.

Neale Watson:
May I suggest that the term sound 'absorption' is misleading.  I'm being picky, but better to stick with the terms 'reflection' and 'transmission':

Soft or irregular surface will minimize reflection;
Soft or irregular surface on thin backing will minimize reflection and do nothing to stop transmission;
Thick and dense material will stop transmission;
Soft or irregular on top of dense material will minimize reflection and transmission;
Dense material with soft material behind it will minimize transmission, but do nothing to minimize reflection

Foam behind a panel helps if it removes air gaps, but otherwise does not 'absorb' sound.

Caleb Dueck:

--- Quote from: Erik Jerde on June 15, 2021, 12:54:29 AM ---
Lastly, as far as the acoustician.  This is their job to figure out.  Thatís part of what youíre paying them for.  You should just be able to set out what you want the room to perform like and they should be able to figure out how to accomplish that.  Of course getting the budget to properly build the design is another thing entirely.  Hopefully youíve got a good acoustician. 

--- End quote ---

This here.

Chris Hindle:

--- Quote from: John Hiemburg on June 14, 2021, 06:39:42 PM ---
 The metal building mfgr recommends spray-in expanding foam insulation for its insulating properties, but I can't find any information on sound absorption for any of the available products.


--- End quote ---
Is the foam to be used to fill a void between inner wall and outer wall, or just as a covering to the inner side of the only wall?
Is the manufacturer intending for an inner "finish" wall to be applied after erection of the pre-fab components?
Any metal left exposed (ceiling) WILL be an acoustical problem.
Chris.

John Hiemburg:

--- Quote from: Erik Jerde on June 15, 2021, 12:54:29 AM ---Thereís a few questions that need to be addressed.  First, like Bob noted spray foam in occupied spaces usually needs to be covered.  Iím not sure how this rule changes for commercial from residential.  When in doubt check with AHJ and mfgr specs.  Lacking a specific code citation mfgr specs win.

Second, what type of foam and to what thickness?  All my experience has been with closed cell foam but there is also open cell foam used in some situations.

Based on my experiences with closed cell foam Iíd expect it to perform like an irregular hard surface.  Fully cured closed cell is quite hard.  Of course you can dent it but I walk on 6Ē of closed cell in my attic with no worry about punching through or otherwise damaging the finished ceiling below.  Stuff is strong.  Definitely is not an absorptive surface.

Lastly, as far as the acoustician.  This is their job to figure out.  Thatís part of what youíre paying them for.  You should just be able to set out what you want the room to perform like and they should be able to figure out how to accomplish that.  Of course getting the budget to properly build the design is another thing entirely.  Hopefully youíve got a good acoustician.  I worked on a project a couple years ago where the building committee went against my advice on acoustician and now the back wall acoustic panels are reflective instead of absorptive.  Ugh.

--- End quote ---


Erik, et al, good points all around. I will look into the question of leaving the foam exposed - it was suggested by one foam manufacturer that it could be painted (good for me) but no mention of it needing to be covered because of fumes/etc. I'll look into it.


As for the acoustician, right on all counts. We have relationship with an excellent company in Australia that has worked on some recent projects for us, and will consult on this one as well. I would like to know and understand for myself going into it. Also at this point insulation is a sizable budget line-item so choosing spray in vs soft goods is an important decision. Having an idea if it is helping or hurting at this stage will certainly help with the math.


Thank you!

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