Drywall/plywood inside stud cavity to add mass?

ScottyMay

New member
Hi y'all
I'm soundproofing what was formerly a garage space. The exterior wall has cedar plank on the outside face, so doing double drywall isn't an option as its outdoors.

What I'm wondering is if I could add a layer of 5/8" drywall or plywood in between the studs inside the cavity? Then I'd put in the insulation and add isolation clips/hat channel, 2 layers of 5/8" drywall with green glue for the wall inside the room.

Is there any reason this would be a bad idea? I'd lose a little bit of the air space in the cavity, but would still have about 4" between the inner and outer drywall layers.

Any other ideas how to add mass on that outside wall? The room isn't really big enough for double stud.

Thanks!
 
I'm very impressed with 18mm MDF. I've just used a couple of layers of 12.5mm drywall (plasterboard here in the UK) and had a similar problem in that the initial idea to use isolation clips and channel ate up too much of the available space. There were also lots of heavier than usual kit to hang on the walls, so I used this extra layer of MDF as the inside surface - it's easy to attach to, and denser than plywood. It has worked extremely well. Walls and ceiling a solid 43mm, and the attenuation is pretty impressive.
 
There is something called a three-leaf system which is bad for sound isolation. I don't remember the details, but the basics is, if there is a 3rd membrane in between two others, it resonates or multiplies the sound, or something like that. You'll have to google it.

I think it would be good if you attach the 5/8 drywall to the inside of the cedar planking. Be sure it is attached solidly. I think that would eliminate the 3rd leaf thing and add mass. Definitely want to use clips for the inside drywall so you don't have sound shorts through the studs.

If you're using regular pink fluffy insulation, you are not really losing the airgap. That stuff is mostly air.

Looks lke you got a decent plan.

Other ideas have more to do with non-sound isolation tricks.

Schedule - If you have to make noise, are you able to do it when it won't bother others. or if you are recording, can you do it at time when there is less noise outside?

In the Box - How much can you get away with by keeping as much in the box as you can? Virtual drums, Virtual guitar amps, etc.

Is sound isolation really necessary? - I personally don't have any real sound isolation. I don't need it. My little studio is kind of detached from the rest of the house. If I get loud, there is only one spot where my family can hear me and that's one of the bathrooms. I don't have any outside noise that leaks in during recording. Heck, I used to have a loud a/c unit and sometimes forgot to turn it off when I was tracking vocals and it never could be heard in the recording.

Do your neighbors really mind? - Went to practice last night. We practice at the guitar players house in his garage. No real sound isolation.... at all. He told us that during the previous practice, the neighbors sat out on their front porch to listen to us while drinking wine.

Anyway... enough rambling....

Good luck with the project.
 
There is something called a three-leaf system which is bad for sound isolation. I don't remember the details, but the basics is, if there is a 3rd membrane in between two others, it resonates or multiplies the sound, or something like that. You'll have to google it.

I think it would be good if you attach the 5/8 drywall to the inside of the cedar planking. Be sure it is attached solidly. I think that would eliminate the 3rd leaf thing and add mass. Definitely want to use clips for the inside drywall so you don't have sound shorts through the studs.

If you're using regular pink fluffy insulation, you are not really losing the airgap. That stuff is mostly air.

Looks lke you got a decent plan.

Other ideas have more to do with non-sound isolation tricks.

Schedule - If you have to make noise, are you able to do it when it won't bother others. or if you are recording, can you do it at time when there is less noise outside?

In the Box - How much can you get away with by keeping as much in the box as you can? Virtual drums, Virtual guitar amps, etc.

Is sound isolation really necessary? - I personally don't have any real sound isolation. I don't need it. My little studio is kind of detached from the rest of the house. If I get loud, there is only one spot where my family can hear me and that's one of the bathrooms. I don't have any outside noise that leaks in during recording. Heck, I used to have a loud a/c unit and sometimes forgot to turn it off when I was tracking vocals and it never could be heard in the recording.

Do your neighbors really mind? - Went to practice last night. We practice at the guitar players house in his garage. No real sound isolation.... at all. He told us that during the previous practice, the neighbors sat out on their front porch to listen to us while drinking wine.

Anyway... enough rambling....

Good luck with the project.

Thanks Chili. I'm in Austin as well and in one of those neighborhoods where they're knocking down and rebuilding a lot. So....I'm trying to future proof against any new highfalutin neighbors that might move in and be less enthusiastic about a rock band next door :P
 
Thanks Chili. I'm in Austin as well and in one of those neighborhoods where they're knocking down and rebuilding a lot. So....I'm trying to future proof against any new highfalutin neighbors that might move in and be less enthusiastic about a rock band next door :P

Sounds like you're east of 35. :thumbs up: Yeah, I think it's good on ya to be proactive now rather than after the complaints start rolling in.

Cool man.
 
There is something called a three-leaf system which is bad for sound isolation.

Correct.

You don't want more than a 2-leaf wall, unless the space between them is quite substantial...IOW, large cavity in-between with 3-leaf may be OK, but generally 2-leaf is the better way to go....especially with smaller cavities in-between.

Here's some pictures:

Understanding the Triple Leaf Effect and air cavity depth | Soundproofing Company

The question I have...is just how much *soundproofing* do you really think you need?
Are you in a noisy area...pissy neighbors...etc....?

Unless you're planning to track Death Metal late into the night with drums banging and guitars raging...you probably don't need as much soundproofing as you think...and instead, focus on making the room sound good if you plan to use it for mixing.
 
Thanks. I am aware of the triple leaf effect. My thought was to snug the layer of drywall/mdf right up against the exterior cedar plank so it wouldn't really be a third leaf. Since I can't add the mass on the exterior, I thought about adding it on the interior.

Death metal, perhaps some day....but it will be a rehearsal space for a full rock band. My neighbors house is about 10 feet away and I really don't know yet how he'll react to the music. I'm less concerned about keeping outside noise out as keeping sound from escaping the room.

This is my first endeavor with trying to build a room "right" so I don't really know what to expect from the clips/hat channel, double 5/8" drywall and green glue. Maybe that's totally fine and I'm just over thinking it?

Any thoughts?
 
... it will be a rehearsal space for a full rock band. My neighbors house is about 10 feet away and I really don't know yet how he'll react to the music.


When you're finished, test the room out...see how well it's working with keeping noise in. If you're a bit concerned after that...try some goodwill...have some pizza delivered to him, and then mention it up-front, tell him to let you know if it's bothersome etc.
I mean...no point in waiting for him to bang on your door...'cuz once that starts, you know he's not going to suddenly be OK with it...but up front, you may be able to head off any issues before they arise, and try and keep it friendly with the neighbor.
 
It's all about the air control. Well sorta lol... No air gaps as well as,,, An air space between two mass loaded walls also helps. No exterioir holes in the walls (WIndows, Air conditioners etc,,,) I'd suggest an indoor unit for humidity control, that is also labelled as an Air conditioner. Or heater depending on climate.
Otherwise,,, Check this out, it will help... STC Ratings
Here's a quick slide show explanation of sorts. www.acoustics.com/tutorial01/slide1.html

If funds available, massloaded vinyl might be considered.
Soundproofing Materials For Effective Noise Control
  • Mass-Loaded Vinyl Sound Barrier. expensive
  • Acoustic Mineral Wool Insulation.
  • Green Glue Soundproofing Compound.
  • Resilient Sound Channels.
  • Soundproof Drywall.
  • Acoustic Caulk/Sealant.
  • Soundproof Foam Panels.
  • Soundproof Blankets.

Maybe note,

- a Drum Room for the drums, (Even Bass if enough room) That'll help with lowend, which is your main focus of control (or it will be lol)
- What db levels are you considering playing at ? Hopefully you don't want 120db live room, lol. Headphones would help a lot if everyone can use them.
- Are you planning on recording / mixing or just live practice ?
- Is there one non-exterior wall ? (Could be the heat/Cooling intake, consider the sound through the ducts)

Just some things off the top of my head...
 
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