Basement adding insulation behind sheetrock - Superior Walls Foundation

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DarkCide

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I'm building my basement and the foundation walls are Superior Walls. They are precast walls with built in 2" Styrofoam R12 insulation.

The walls are ready for sheetrock. I am considering adding additional foam or fiberglass insulation behind the sheetrock for sound deadening properties. The additional insulation would sit against the built in Styrofoam.

Would adding additional insulation make any difference in sound dampening characteristics in the basement?

If I install the sheetrock without additional insulation there would be a 6" gap between the Styrofoam and the sheetrock.

The basement will be a home recording studio / music room.

Here's what Superior Walls looks like:

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To stop low frequencies you need density, not air. If you put anything in there (other than sand or concrete, say), use rockwool (e.g., Safe'n'Sound) is my $.02. The cost over regular insulation is modest, and it's going to be much more effective, though 6" of R12 is going to be better than styrofoam (pretty good for shipping stuff).
 
You use the phrase "sound dampening" but you're not really being specific in what you want to achieve. There are two purposes for controlling sound in a studio: 1) To prevent sound from entering or escaping a studio. Keeping extraneous noise out of the recordings and keep loud instruments from bothering the neighbors, or; 2) Provide acoustic treatment in the studio to provide for a flat responding room, so instruments sound better and you can accurately hear your mixes.

Which of these purposes would you want to add the additional insulation for? If it is to prevent more sound from entering or leaving the studio, you're in a basement and the ground surrounding the basement should be good enough. Plus the cast concrete walls have a lot of mass, insulation is not going to add benefit.

If it is to acoustically treat the room, then putting it behind the sheetrock would severely limit it's ability to absorb sound. You might be adding a little absorption at some really low freqs, but you would get more bang for the buck if your acoustic treatment was on the people side of the sheetrock.

In either case, my vote is No, don't bother with adding more insulation between the walls and the sheetrock.
 
The only big benefit of any insulation behind the drywall in that basement would be for temp control, if needed, like if you are in a northern area where winter temps get real cold, the cement walls will get cold and pass some of that into the space. Yeah, the insulation will add a bit more dampening, but you really want to decouple the drywall.

For real sound deadening/dampening, you should decouple the drywall from the studs using resilient sound clips and hat channel furring, to which you then attach the drywall.
That also calls for a double drywall...and that will decouple the interior room from the studs, the cement and the ceiling (you do the same there).

If you have the height in the basement, may also want to decouple the floor from the rest of the structure/house by doing a raised floor, frame on rubber isolation bushing, and then put some insulation in there too if you don't want a cold floor, plywood and then whatever you want on top.

The idea is that with the double drywall decoupled from the studs, and the decoupled floor...and you don't connect the floor or the walls or ceiling to each other at their joints, you leave a 1/4" space and then use a flexible acoustic caulk in the joints...the sound in the room is not getting transmitted to the rest of the structure, and vice-versa, sound from the outside and the structure is not getting transmitted into the room.

How much absolute *soundproofing* you really need, will determine how much mass you need...but decoupling will be necessary and give you the best case situation, other than doing a double-wall, double drywall and basically floating an entire room-in-room...which does a great job, but may not be easy or even necessary to do in more typical home studio situation.

So much depends on what it is you are planning to do in that room, which you don't really say the type of use it will have...since it could be full band scenarios, or one person working on beats using synths and sample, each needing more or less treatments and room design considerations.
 
If you put sheetrock over those studs without any dampening you are creating resonant cavities with a diaphragm over them (the sheetrock) and they are going to resonate and create nasty sounds when stimulated at certain frequencies. The metal studs will make this worse as they don't provide the dampening that wood would provide. The thinner the drywall, the bigger the problem. Two layers of different thicknesses of drywall might not resonate much, but you don't need to worry about limiting transmission because these are concrete walls with the earth on the other side, and little sound is going to penetrate that. Also, fiberglass or Rockwool is a lot cheaper than the second layer of drywall. Insulation in the ceiling will also do a lot to even out the low-frequency response of the room, so I would do that at least over the recording and control room area.

The point here is to keep the wall from acting as a resonator, not to block sound transmission through the walls. You'll still need to do sound treatment in the room to control reflections (both absorption and diffusion)
 
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