Soundproofing- Worth Going 3 Layers of 5/8th?

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Ghostnote

Guest
Yeah, I wasn't going to use any green glue or whisper clips, etc, as I am going with a completely decoupled room-in-a-room build and they don't provide any advantage for double wall assembly. The only flanking path would be the concrete slab that both the inner and outer walls would be sitting on. I'm not worried about that however, as I have already pounded directly on the slab with a hammer while my girlfriend went into all parts of the house and the basement suite and she couldn't hear it at all, so I don't think the slab will transmit any sound.

I will be very careful to ensure that all surfaces are airtight and that the airspace between the inner and outer walls and ceilings isn't shorted out anywhere. I'm also going to use double solid core doors that have been bulked up with 3/4 plywood on both sides and ensure that they seal airtight, so I don't forsee a weakness there.

My only real concern was if a 3rd layer of drywall would reduce the sound escaping the room enough to justify the added time, work, and expense.
 

trynberg

Senior Member
There is zero point to using Green Glue or other damping compounds if it is a true double-stud construction. Save your money.

The large air space in a double-stud construction pushes the cavity resonance pretty far down, into the region where only bass drum fundamental and low bass notes produce significant energy. Unlike a single-stud wall, the mass-controlled regime isn't so important.
 

octatonic

Senior Member
You want an air gap, ideally.
And you want to float the floor.

If you are going to layer up gyprock then at least use green glue between the layers.
I can't see any real reason for the 3rd layer though, especially with live drums.
 

WallyY

Platinum Member
1 outside layer and two inside layers with a damper like green glue in between the two inside layers.

But most of the sound will get out through flanking paths, door etc..

You're raising the resonant frequency of the walls so the bass won't go too far.
 

trynberg

Senior Member
If this is wood framing, there will be essentially no improvement in sound isolation by adding the third layer, except for below the resonance of the stud cavity. Most likely not worth it, especially as there are probably numerous flanking paths anyway.

EDIT: Sorry, read too fast. If this is truly a decoupled space with independent stud rows, then yes, adding a 3rd layer to each side would be expected to slight increase performance. However, my point above stands that, given the likelihood of flanking paths, there is little point to adding a 3rd layer.
 

larryace

"Uncle Larry"
It's the air space/decoupling between the 2 rooms within each other that does the soundproofing. That said, 3 layers of 5/8th's couldn't hurt. However, I'm not sure it's necessary.
 
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Ghostnote

Guest
I'm building a room-in-a-room jam space in my garage and was wondering if it's worth the expense to add a third layer of 5/8ths drywall to my inner and outer walls, or is 2 layers of 5/8ths kinda the point of diminishing returns?
 
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