get R30+sound absorption with 2x12” exposed ceiling joists?

[newstudio2007]

I’m about to build a new studio control room from the ground up. Conventional construction: wood frame, drywall, and a flat, almost horizontal roof One room - about 15 x 25 feet with an 11’ ceiling. The room will be used mostly for mixing, with some overdubbing. (musicians in the same room - headphones for all)

In an effort to keep our costs down, the idea was to have exposed ceiling joists (2x12” beams with 16" centers) ... and have the exposed fiberglass insulation absorb sound, (possibly stapled up by the paper backing) and basically, in a way, make the ceiling 'disappear' - acoustically speaking (more or less)

However I'm very hesitant to have any chance of any exposed fiberglass fibers... due to possible long term health concerns.

The joists will run the short way across the room - so the roof joists will be approx 15' long....

The plan was to NOT seal in the fiberglass behind any fiber, gypsum... so it would be open to absorb sound.

Once we are done - if you look up in the finished room, you'd see the exposed 2" edges of the roof joists... and whatever material is stuffed between the joists to provide the R30 insulation that the city requires...

Any clever ideas about how to achieve the necessary R30 insulation between the exposed 2x12” ceiling joists… and also have that same insulation absorb sound? (and look decent too)

Thanks!

[bpape]

Quite honestly, that's too much absorbtion all in one dimension. It's at least somewhat broadband though. The other drawback is that you'll have just about zero isolation from the outside world and the noise floor of the room will suffer.

Bryan

[jwl]

bpape gives good advice concerning isolation here.

But if you go this route, and if you are concerned about the health risks of fiberglass, then consider using Ultratouch cotton insulation between the joists. It performs well acoustically, and I believe it now comes in R30 (in addition to the R19 and R13 that have been available for a while).

I'd consider a membrane-type approach for much of the room, with just the absorbing material (and cloth or whatever you will cover it with) in strategic locations, ie, above the mix position and above where the drums will be set up when you record. This will reduce the amount by which you deaden the room, while still getting as much bass trapping as possible.

[bpape]

The cotton is an excellent choice for broadband absorbtion in the corners and up in the joists (around the perimeter and as a cloud for the mix position). You can potentially build some tuned panel absorbers like those shown on Ethan's site for the rear wall to deal with specific issues that are common there.

Make sure to consider some 2-4" panels directly behind the monitors to deal with SBIR (speaker/boundary related bass response issues)


For the rest, making all of the other panels more broadband will help keep a smooth response. How much HF absorbtion you can tolerate will depend on how you choose to do the floor.

To liven things up and give a nice lively sense of space, diffusion on the rear half of the side walls would be an excellent addition to the treatment plan.

Bryan

[newstudio2007]

Originally Posted by bpape

Quite honestly, that's too much absorbtion all in one dimension. It's at least somewhat broadband though. The other drawback is that you'll have just about zero isolation from the outside world and the noise floor of the room will suffer.

Bryan

thanks for the thoughts....

however.... i disagree about "too much absorption" - as the hardwood floor is almost parallel...

and... the roof is VERY substantial.... so how is it that i'll have just about zero isolation from the outside world?

[jwl]

"just about zero" isolation may be overstating it. :-)

Bpape does have a good point though, isolation will not be maximized with what you are describing. Perhaps more accurate than "just about zero" would be "tens of dB less isolation across all frequencies than you could get with a two-leaf, room-within-room structure built correctly with adequate mass and airtightness." Or something. :-)

It really depends on the construction of the present roof assembly, how much noise is around your building, and how much noise you are willing to live with.

Of biggest concern will be low end. Trains, trucks, planes, etc etc will be easier to hear in the studio. Similarly, drums and bass amps will be easier to hear outside the studio.

Doing what you are doing now will improve isolation noticeably. Note that a 3dB improvement is noticeable; whereas the levels bpape is thinking of is more on the order of 20-30dB. Not sure how much you'll get with this design; measure before and after and see.

Another thing you can try is put your ear to the ground when something noisy from outside happens, with some low end energy, and see if you can here it through the floor. That'll give you some idea as well.

[newstudio2007]

Originally Posted by jwl

"just about zero" isolation may be overstating it. :-)

Bpape does have a good point though, isolation will not be maximized with what you are describing. Perhaps more accurate than "just about zero" would be "tens of dB less isolation across all frequencies than you could get with a two-leaf, room-within-room structure built correctly with adequate mass and airtightness." Or something. :-)

It really depends on the construction of the present roof assembly, how much noise is around your building, and how much noise you are willing to live with.

Of biggest concern will be low end. Trains, trucks, planes, etc etc will be easier to hear in the studio. Similarly, drums and bass amps will be easier to hear outside the studio.

Doing what you are doing now will improve isolation noticeably. Note that a 3dB improvement is noticeable; whereas the levels bpape is thinking of is more on the order of 20-30dB. Not sure how much you'll get with this design; measure before and after and see.

Another thing you can try is put your ear to the ground when something noisy from outside happens, with some low end energy, and see if you can here it through the floor. That'll give you some idea as well.

I guess you missed the info in the original thread - the studio will be build from the ground up.

[newstudio2007]

So - my question is intentionally limited to room acoustics .... and how to deaden down the ceiling - within the confines of 2 x 12" exposed ceiling joists..... on a 16" center.... for simplicity... and it is the only big problem that I have right now.

Sound isolation is well taken care of.

What about if we use 6 mil poly for a plastic layer below the joists (or maybe Tyvek ?) - with the assembly completely sealed at the perimeter and at all laps - to contain the loose fiberglass insulation.

Then a layer of pegboard nailed up in big sheets

Then completely covered in 2" echo eliminator acoustical cotton material.

Soundproofing Products Walls Ceilings Floors - Echo Eliminator.com

How does that sound?

[dcharrison]

If extraordinary measures are not taken to avoid it, there will be serious sound conduction problems through your roof. That means no open mics when it rains and retakes if a plane flies by.

Lots of project studios are stuck with these limitations. Fixing this requires decoupling the roof from the ceiling--a non-trivial matter.

You can mitigate the problem somewhat by using a heavy membrane barrier underneath the roof and above the sound absorber. Let the material drape down a few inches and you will get a little "limp mass" absorption in addition to the barrier effect. You will still have conduction through the joists.

I agree that covering 100% of your ceiling with broadband absorption might be too much. Consider running 1x2 or 1x4 slats perpendicular to the roof joists every 2 to 6 inches. This will let you keep some mid to hi reflections and it will also give you something to lay your insulation on. Staple some dark colored (Fire retardant) fabric under the slats and it will look like a million bucks.

[bpape]

Agreed.

As to the in-room, I still think it's too much all in one dimension. I have no problem with some perimeter for bottom end control and a 'cloud' where necessary but I really don't think you want the whole ceiling totally and competely dead like that.

That introduces a TON of high frequency absorbtion in the room limiting what you can do in other places where it's also needed without overdamping the high end.

Just my opinion.

Bryan

[newstudio2007]

Originally Posted by bpape

Agreed.

As to the in-room, I still think it's too much all in one dimension. I have no problem with some perimeter for bottom end control and a 'cloud' where necessary but I really don't think you want the whole ceiling totally and competely dead like that.

That introduces a TON of high frequency absorbtion in the room limiting what you can do in other places where it's also needed without overdamping the high end.

Just my opinion.

Bryan

Thanks for the thoughts....

There will be a lot of windows and glass in the room, and a wood floor...so I think that plenty of broad band absorption will work out to be a good thing....