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Inner shell ceiling idea
Old 7th October 2019
  #1
Inner shell ceiling idea

Just thought I'd float this idea out there for some feedback. I'm working on a single room design in an existing room with a 9' ceiling. My outer shell is defined by the existing ceiling which is drywall under a larger garage/loft space.

I've been trying to come up with a way to balance soundproofing with acoustic treatment while maintaining the max available height. It will be a room-in-room design, so I know the air gap is important. But because of the low ceiling, I think a full "cloud" will also be appropriate to help provide the illusion of a taller room. This design borrows from the inside out concept, but it's really neither inside out nor outside in. I suppose it's a combination of both.

I wanted a final 8' height but this ended up being a bit less at 7'9". But again it does include treatment. The 5" air gap is not great but I think (based on MAM calculations), it will provide sufficient soundproofing for my situation. The walls will have a larger gap, thus making the ceiling the weakest link.

Of course this is just one small detail. The rest of the design will be important as well. I intend to do plenty of bass trapping in the corners and possibly something similar to this in the walls. In any case, what do you guys think?

Old 10th October 2019
  #2
Maybe a bump will help...
Old 12th October 2019
  #3
Lives for gear
Seems like it should work, from my understanding it really isn't going to matter where the framing is...

My concerns would be in the practicality of building it and maybe more so sealing it up. How do you attach the inner leaf drywall to the 2x3's? And then you would have to cut the drywall, put the GG, add the 2nd sheet, attach the fluffy, hoist all that up and then put the 2x3 up?

It seems it would be really difficult to lap the seams in the drywall doing it that way.

I would probably change the upper sheet of the inner leaf of drywall to OSB, so at least you could suck it down from the bottom with screws.

Not sure what your span is, but what about double 2x8's or 2x6 even joists, put just 1/2"-3/4 below the outer leaf. Then drywall the bottom of those and run some 2x4's perpendicular to them?


From your pics so far though you look like a very accomplished builder...you probably have a better plan.
Old 14th October 2019
  #4
Not really an accomplished builder, but I'm slowly getting there. It's just becoming harder and harder to bounce ideas of of experienced folks on these forums. Sign of the times I suppose.

While most of this DIY studio stuff is based on tried and true ideas repeated verbatim, it's not out of the question for someone to come up with something new-ish. Although this is not 100% original. The Sayers site is where I got some of the concepts to build on here. But generating discussion there is even more difficult than on GS.

Anyway, as the drawing shows, it's a 16' span. 2x8 doesn't seem quite enough but 2x10 is plenty, and the size provides some advantages to the overall assembly.

The idea would be to get all the joists up first with some insulation laying on top.

Then build the ceiling in sections. A 2x3 frame, 2' x 8', sized to fit between the joists with about 1/4" gap.

Place the first piece of drywall (or OSB) over the frame and secure to make it rigid.

Then add the GG and 2nd layer of drywall. At this point it would only weigh slightly more than one whole piece of drywall. But half the size.

Raise it up with a hoist into the gap between joists, then attach to the joists with structural screws through the 2x3 frame and caulk the perimeter.

Repeat for each section and you have a sealed ceiling. From my limited experience it sounds about equally as difficult as a conventional ceiling with 2 layers of drywall. They both bring their own challenges. For example, no mudding/sanding of the drywall required here!

This would be a good time to run electrical in the air gaps below the ceiling.

Now cut the 70x insulation to fit between the joists. The 2x3 will act as a backstop, enforcing the 2 1/2" gap above the insulation. You can also attach the insulation to the 2x3.

Finally finish with fabric and slats if necessary to bring back some live-ness.

Again the idea was to maximize space and utility as much as possible. I'm feeling pretty good about this approach but I may be missing something...
Old 14th October 2019
  #5
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Jason Foi's Avatar
 

Looks good to me
Old 20th October 2019
  #6
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chrismeraz's Avatar
 

In my experience a 4-inch cloud won’t help very much at all. Mine is 16 inches and it works only because my monitors don’t go below 45Hz. I apologize for bringing the crude reality. I know how disheartening it is.
Old 24th October 2019
  #7
Wow, that's the first I've heard that. I thought the typical application was usually 2" air + 2" absorber or 4" + 4". I'm just doing a hybrid of that due to space constraints.

I'm not expecting the cloud to handle low frequencies, only to help raise the perceived acoustical ceiling. I plan to have a number of bass traps in the room for the lows. Not entirely sure yet but I expect the back wall will have something close to 16" for that purpose. And of course there will be corner traps & possibly a waveguide in front.
Old 24th October 2019
  #8
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Typical recommendation is 4",4" minimum for a first reflection point. The ceiling you are making should be good down to about 150-200hz unless you use those slats to handle your height mode of ~60somethinhz. Dont include slats in a first reflection point though, obviously. None the less, your plan is sound.
Old 8th November 2019
  #9
Moderator
 
Northward's Avatar
Quote:
Originally Posted by thechrisl View Post
Just thought I'd float this idea out there for some feedback. I'm working on a single room design in an existing room with a 9' ceiling. My outer shell is defined by the existing ceiling which is drywall under a larger garage/loft space.

I've been trying to come up with a way to balance soundproofing with acoustic treatment while maintaining the max available height. It will be a room-in-room design, so I know the air gap is important. But because of the low ceiling, I think a full "cloud" will also be appropriate to help provide the illusion of a taller room. This design borrows from the inside out concept, but it's really neither inside out nor outside in. I suppose it's a combination of both.

I wanted a final 8' height but this ended up being a bit less at 7'9". But again it does include treatment. The 5" air gap is not great but I think (based on MAM calculations), it will provide sufficient soundproofing for my situation. The walls will have a larger gap, thus making the ceiling the weakest link.

Of course this is just one small detail. The rest of the design will be important as well. I intend to do plenty of bass trapping in the corners and possibly something similar to this in the walls. In any case, what do you guys think?

- Get rid of all drywall under garage / loft. You'll have to fill the cavity with 2.0-2.5PCF rockwool but only while you build the studio shell's ceiling structure so you can have access with small format tools in the meantime etc.

- Get new studio shell ceiling joists about 2" lower than existing joists and make sure you have perimeter joists all the way sealing the assembly properly. Brace structure well.

- As you install the studios shell joists, cover the top of joists with 2x 3/4" high quality OSB (not plywood), screw and glue to joists. They will hover about 14mm 1/2" under the existing building structure.

- Once done, add more mass in-between the joists with heavy drywall. A lot more than on your drawing. Take in account MAM with floor of garage/loft above.

- Skip green glue. It's a waste of your budget and time.

This should give you maximum usable height.
Old 8th November 2019
  #10
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Quote:
Originally Posted by Northward View Post
high quality OSB (not plywood)
For economical reasons?
Old 8th November 2019
  #11
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Jason Foi's Avatar
 

Quote:
Originally Posted by Northward View Post
- Get rid of all drywall under garage / loft. You'll have to fill the cavity with 2.0-2.5PCF rockwool but only while you build the studio shell's ceiling structure so you can have access with small format tools in the meantime etc.

- Get new studio shell ceiling joists about 2" lower than existing joists and make sure you have perimeter joists all the way sealing the assembly properly. Brace structure well.

- As you install the studios shell joists, cover the top of joists with 2x 3/4" high quality OSB (not plywood), screw and glue to joists. They will hover about 14mm 1/2" under the existing building structure.

- Once done, add more mass in-between the joists with heavy drywall. A lot more than on your drawing. Take in account MAM with floor of garage/loft above.

- Skip green glue. It's a waste of your budget and time.

This should give you maximum usable height.
Isn't that creating just a single leaf partition??
Old 8th November 2019
  #12
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Quote:
Originally Posted by JayPee View Post
For economical reasons?
Osb has high shear strength, its structural i assume, but im curious too.
Old 8th November 2019
  #13
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Northward's Avatar
Quote:
Originally Posted by Jason Foi View Post
Isn't that creating just a single leaf partition??
Not if there is a floor above... Which could also see mass added to further improve numbers.

The way he decided to work initially is a triple leaf.

Most modern studio shells are single but heavy leaf structures. The second leaf not being on the studio shell's floating floor (e.g. it's the existing building's structural wall) or being on another floating floor (adjacent room, like a Live Room).
Old 8th November 2019
  #14
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Quote:
Originally Posted by Northward View Post
Not if there is a floor above... Which could also see mass added to further improve numbers.

The way he decided to work initially is a triple leaf.

Most modern studio shells are single but heavy leaf structures. The second leaf not being on the studio shell's floating floor (e.g. it's the existing building's structural wall) or being on another floating floor (adjacent room, like a Live Room).
Hmmm, i only see a 2 leaf decoupled partition in his drawing, but perhaps you are correct. The word loft does imply a floor would be there.
Old 8th November 2019
  #15
This should give you an idea of the big picture. The loft/garage area is relatively large and has lots of ventilation to the outside (mainly soffit vents). It extends about 25 feet beyond what's shown in the drawing. I only show a couple trusses but of course they extend throughout the entire building, every 24 inches.



I explored the question of whether that would really be considered a leaf in this thread & the conclusion was that it was a weak leaf at best due to the distances involved and lack of air tight boundaries.

That's what led me to conclude that I'm not dealing with a true three leaf situation.

Believe me I would love to raise the ceiling here. It keeps me up at night as I struggle with how far down the rabbit hole I should be going. But as you can see, it would involve a total redesign of the building structure (since these are trusses, not joists). This is an area where I had to reluctantly draw the line and decide to work with what I have. I have a 9' ceiling which is one foot more than the average "bedroom" type studio. So my idea with this thread was to absolutely squeeze the most use out of that foot (OK 14 inches). While certainly not as good as a taller room, it does provide for the inner leaf, air gap and ceiling cloud.

My understanding is that a mostly absorptive ceiling like this can help make it sound taller (psycho-acoustically, not magically). I've read this on several occasions as it refers to recording drums and other instruments. Of course it assumes the rest of the room has decent treatment and adequate bass trapping.

This is a single room studio. I've been exploring best options as far as the optimal design approach in other threads. And I do realize the best option would be to start with a whole new & larger building.

As for Green Glue, I know that is a contentious subject. The conclusion I eventually came to is that when used between larger sheets of material it does little to affect mass law, contains no magical properties, but does assist with damping. I was under the impression that it ultimately helped lower the resonant frequency a bit. I believe I recall reading that it has about the same effect on resonant frequency as an extra layer of drywall. And, for what I refer to as the outer leaf here, I've been told by a structural engineer that I would be OK to add another layer of drywall -- but no more than that!
Attached Thumbnails
Inner shell ceiling idea-built-frame-1.jpg  
Old 8th November 2019
  #16
I should point out that I am always open to learning how this stuff works, especially if I've drawn inaccurate conclusions. And I do appreciate the responses. I guess the question no one can answer definitively is, how much compromise is acceptable on that spectrum between an 8x8x8 room and Blackbird Studio C? I'm still trying to figure that out myself...

So, isolation wise, I ran the numbers on this ceiling through a MAM calculator (sorry I forget who's it is) and came up with this curve in black. The floor is a concrete slab and the walls will all have similar makeup -- probably with a larger gap. This doesn't include any effects associated with Green Glue (or not).



This is OK, but not great. If I add a 3rd layer of drywall to the inner leaf, it only helps the resonant freq by about 3Hz. And as I said before I can't add more mass to the outer leaf.

I'm not concerned with inside noise getting out, only outside noise getting in.

Here is probably the worst case scenario. We get low flying helicopters, perhaps once a week. I took this measurement a couple years ago when I managed to catch one at the right time.



This is my train of thought. At 32Hz:
The noise is about 75dB.
Hearing threshold is about 55dB
NR10 is about 62dB
My room would block about 15dB

So I should hear about 60dB. Audible, but still within NR10. And honestly with HVAC and construction imperfections I'll be happy if I can get NR15 or even NR20.

Of course above resonant frequency things get dramatically better.

Is this a reasonable approach or am I missing something? At the very least I'd like to think I have an isolation strategy I can live with, even if I'm still unsure about the acoustic treatment...
Attached Thumbnails
Inner shell ceiling idea-mam1.jpg   Inner shell ceiling idea-helo2.jpg  

Last edited by thechrisl; 8th November 2019 at 07:00 PM.. Reason: more words
Old 4 weeks ago
  #17
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Northward's Avatar
The structure feels particularly weak to me. Maybe add a couple of intermediate posts and a beam in there to reduce span and get load bearing to a higher figure.

Even if the loft space in your case is just a cavity and not a storage or accommodation, so no floor installed, I'd still somehow try and isolate by the top to gain some height and cavity depth. Obviously I have little detail about your project, so can't say how easy it would be to seal the perimeter.

You're being very optimistic with your NR values. It takes a lot of mass and proper floating to actually get to NR15. Don't forget flanking either (solidian noise).

I feel that for studios, the NR curve values should be adapted in the LF... Lowered by at least 9 dB. But that's another subject.
Old 4 weeks ago
  #18
Quote:
Originally Posted by Northward View Post
The structure feels particularly weak to me. Maybe add a couple of intermediate posts and a beam in there to reduce span and get load bearing to a higher figure.
Are you referring to the existing structure or the inner leaf idea I started the thread with?

The existing structure has been checked out by an engineer and approved for the double drywall ceiling. Again in my drawing there is truss every 24 inches.

For the inner leaf, those are 2x8 on a 16' span, 24in spacing. I figured all the materials would add up to around 8psf. With 10/15 live/dead load & L/240, I should be good for a 19' span. Not a structural engineer but this is what the calculator kicks out assuming I used adequate input values.

Quote:
Even if the loft space in your case is just a cavity and not a storage or accommodation, so no floor installed, I'd still somehow try and isolate by the top to gain some height and cavity depth. Obviously I have little detail about your project, so can't say how easy it would be to seal the perimeter.
The trusses are only 2x4. I did think about removing the existing drywall and insulation, then putting it back on the top side. But that would gain me 3.5 inches and yes I'd have to seal around every one of those trusses. Just doesn't seem worth it for such little gain.

I haven't looked into the cost of rebuilding 10 trusses to allow a couple more feet of height (scissors perhaps) but I'd be real surprised if wasn't a $25k job, which to be honest, isn't that far from my total budget.


Quote:
You're being very optimistic with your NR values. It takes a lot of mass and proper floating to actually get to NR15. Don't forget flanking either (solidian noise).

I feel that for studios, the NR curve values should be adapted in the LF... Lowered by at least 9 dB. But that's another subject.
This sounds about right. I figured a standard concrete slab is the next best thing to an engineered slab which is the next best thing to a floating floor. The good news is that I have decent control over what goes on in this building and the acreage it sits on. My primary concern is the environment beyond that. Maybe there is more potential for flanking airborne noise via the slab than I realized.

But outside the slab, I would think the MAM calculator is telling me what to expect, right? Though I understand this is perfect world calculation.
Old 4 weeks ago
  #19
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I wonder for that size space if you could close up all the roof vents, and use a fan with an isolator box on both gables to cycle in outside air?

I know my current place has a fan like that and very similar construction, after some hailstorms roofers have added vents- because I guess that is what they do no matter what anymore, but there were none originally and no sign of condensation issues. That said Denver is a pretty arid climate...

If so, one idea I had was to put inner framing joists directly below outer and build boxes that go up into the attic space above, fill mostly with insulation.
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