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PostPosted: Thu Mar 04, 2021 3:49 am 
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Location: Chicago, IL
So if I'm going M-A-M, there'd be drywall attached to the underside of the joists, forming the ceiling of the interior room, and drywall sitting on top of the joists for the external mass? And could interior mass be attached via the hat-channels as well? Combining those ideas, if you will?


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PostPosted: Thu Mar 04, 2021 10:48 am 
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if you're doing M-A-M assembly the "exterior" mass would be either the floor enhancement (larger air gap between mass layers), or the mass on the bottom of the joists with the air between the mass and floor filled with insulation. and then the "interior" mass on the inside of the inner room framing (normal) or on the outside of the inner room framing (for inside out).

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PostPosted: Fri Mar 05, 2021 6:31 am 
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Gotcha, thanks!

Would the hat-channel be better than inside-out for the interior leaf?


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PostPosted: Fri Mar 05, 2021 4:22 pm 
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if you have a separate frame - just go with the frame, the iso-clip/hat channel can actually reduce some of the isolation compared to just the frame and mass. iso-clips and hat channel are, most times, a second choice when it comes to isolation. where you would see a benefit is it you have a lot of structural transfer via the floor or other structure members. the inner framing should be secured using isolation sway bracing. in some locations this may also be a code requirement.

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PostPosted: Thu Mar 11, 2021 7:24 am 
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Hey Glenn,

Could you point me in a direction for fabric for an inside-out ceiling? I'd also use this on the walls. Just not sure what to even Google.

Thanks so much!


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PostPosted: Fri Mar 12, 2021 2:06 am 
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you'll need a fire re-tar-dant cloth - either bulk purchase and treat yourself, or purchase from a known source of fire-safe fabric. it should be acoustically transparent but woven tight enough to contain any loose fibers from the insulation. you can use an upholstery type of insulation like a dacron or equiv sheet to help both contain fibers and even out the surface.

so products like Guilford of Maine are well known (but generally expensive), and there are products like window curtains that generally will be fire-safe and may address your needs (and likely be less expensive) - check fabric shops and also wholesalers in your area.

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PostPosted: Fri Mar 12, 2021 5:40 am 
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Thanks for the tips. So sorry to keep hammering on with more questions, but I keep hitting new ones...

1) I think I need a sanity check on the broad strokes plan: My current plan is for the walls to be conventionally built (AKA NOT inside-out), but the ceiling IS inside-out. That decision was based on inside-out giving a better chance of a good seal, and potentially easier to install for the contractor since it can be done in panels. So, is that combo of conventional wall leaf but inside-out ceiling an alright approach? I think this is what John is suggesting here:http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm, but maybe I'm misinterpreting his diagrams.

2) Following from the above question, I'm realizing that I have this plan to cover the drywalled walls with fabric, and don't remember why :oops: Do I even need this, or should I just mud/paint the drywall for the walls? There will be rugs on the floor, lots of sound-absorption panels in the corners and hanging from walls, and the inside-out ceiling. Perhaps those elements are enough to tame reflections...?

Hoo boy, thanks so much for your responses already, Glenn. I really really appreciate it!!

Ben


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PostPosted: Sat Mar 13, 2021 2:49 am 
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the inside-out approach is good when you need a lot of coverage - for example smaller isolation rooms, control rooms where you'll add some HF support panels later, etc. in a living space, mastering room, etc then normal construction is usually the way to go.

and of course you can use a combination.

at the end of the day, the frame itself is basically the same - some differences in placement of edge nailers - its where you place the mass. so having the ceiling joists "exposed" wouldn't be too different than say a semi-finished basement. in this case the "exposed sub-floor" is your inside-out mass layer on your inner ceiling frame.

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