Reflector/Absorber Sandwich?

Voltron

Active Member
I am considering upgrading the sound properties of a common wall between my listening space and exterior noise sources.

Without invasive demolition, I am expecting standard 2X4 framing with 1/2 inch drywall on both surfaces.

I am considering using adhesive to attach 3/8" tempered hardboard (perforated or not) to the back of the noisy side panel. Next, Roxul 3 1/2" Safe n Sound mineral wool bats between the hard board and the listening side panel.

What are your opinions/experience with this proposal? Hardboard, perforated or not? Would acoustiwall panels be preferable over re drywalling?
 
Hi Voltron,

If your main goal is to prevent the outside noise from entering your listening space, the best (really, only..) solution is more mass. The easiest and cheapest way to do this is by doubling the drywall, just glue another sheet of drywall directly to the existing. Stagger the joints so the "cracks" between the drywall sheets don't line up. You can't really "reflect" outside noise away - but mass will stop it. Then you can treat the inside if needed or desired to optimize your listening space.
 
Just don't use any mayonaise, it goes bad quick and starts to stink the place up within a few hours.

Dave
 
Hi Voltron,

If your main goal is to prevent the outside noise from entering your listening space, the best (really, only..) solution is more mass.
Easiest solution, but far from only. Widening the wall helps keep low frequencies from going through. Adding a furring or changing the wall to something decoupled would have a very big effect.

You could even do better than just adding a layer of gyp without changing the structure at all. You can add a layer of gyp over green glue or the like. Or, instead of a layer of plain gyp, you could add a layer of QuietRock (or similar) for a pretty big improvement.

The easiest and cheapest way to do this is by doubling the drywall, just glue another sheet of drywall directly to the existing. Stagger the joints so the "cracks" between the drywall sheets don't line up.
It is the easiest and the cheapest, but I don't know if it'd be a lot more to add green glue.

You can't really "reflect" outside noise away - but mass will stop it.
That's actually what happens to most of the sound that doesn't get through your wall, it bounces away. Higher mass means bigger impedance change between air and wall, so there's a less efficient energy transfer between the two mediums. What doesn't get transferred to the wall gets bounced away. This happens in all mediums, not just air. Most of the vibration traveling through a board will bounce back when it reaches the end of the board for the same reason, because there's a big impedance change where the board meets air. Some sound is absorbed as heat into the wall panels, and some of it is trapped in insulation (becoming heat).

Without invasive demolition, I am expecting standard 2X4 framing with 1/2 inch drywall on both surfaces.
That would be pretty flimsy for an exterior partition. There's at least going to be insulation, and I don't think you can get type X in any size other than 5/8. Type X is the stuff with fiberglass infused and it's required for walls with a fire rating, as the fiberglass holds the gypsum together after the paper burns off. Anyway, you'd expect to find 5/8 on at least one side, and usually exterior studs are bigger than 2x4.

Putting perforated board over the insulation will basically mean it won't help reduce sound transmission through the wall, but it will help with absorption because it lets the sound through to the insulation where it gets sucked up.

Non-perforated will mean it's acting like an insulated furring. That will increase transmission loss, but it won't do anything for absorption, except at low frequencies where the board will act like a panel resonator.
 
Without invasive demolition, I am expecting standard 2X4 framing with 1/2 inch drywall on both surfaces.

You're going to add another interior wall to your existing exterior wall? If so, you are going to add the 1/2" drywall before you stand the walls up?

I am considering using adhesive to attach 3/8" tempered hardboard (perforated or not) to the back of the noisy side panel.
I've never seen 3/8" hardboard, only 1/4" or less.

And yes, they make 1/2" type-X gyp board. What's green glue and how do you use it?
 
Green Glue is goop that you use to glue two pieces of drywall together. It adds a dampening layer that absorbs some sound energy. It's not a magic bullet, but it's a step up from just screwing on another layer of gyp.
 
I haven't read every word of this thread, but wonder if you've considered sound deadening wall board. I find nothing works quite as well at controlling acoustics than something engineered specifically to do it.

There's GP Hushboard (which I think goes behind regular drywall):
http://www.gp.com/build/product.aspx?pid=1071

There's Quiet Rock drywall:
http://www.quietrock.com/

There's Noise Stop that goes behind drywall:
http://www.acousticalsurfaces.com/acousti_board/acousti_board.htm

I know there are others, and some are quite inexpensive. I'll try to remeber more brand names.....

EDIT TO ADD:

The product i was trying to remember is Soundstop by Knight Celotex. It also gets installed as a backer to regular drywall:
http://greensounddeadening.wordpress.com/
 
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I haven't read every word of this thread, but wonder if you've considered sound deadening wall board. I find nothing works quite as well at controlling acoustics than something engineered specifically to do it.
I did mention it, and it is good stuff, but a properly built wall is better. Of course, it's not always possible to go back and add a furring or a second stud row, so add-on dampened drywall products like QuietRock become the next best option (although they are very expensive).
 
Hard to find those fancy products down at Home Depot, but your plain Jane wall sheathing fiberboard is the same thing, used to be called Buffalo Board.

Doesn't the drywall screws transfer sound threw to the studs and thus threw the wall? Maybe your drywall/fiber board/drywall sandwich needs to be glued together? We used to have to glue fabric covered prefinished drywall to steel studs with PL 400 adhesive and wedge them to the studs with temporary wood cross bracing
 
Just to make sure there's no confusion, QuietRock is a sandwich made of multiple thin layers of drywall, an inner layer (sometimes metal), and a resilient glue/resin. It's not at all similar to fiberboard and definitely not available at Home Depot. It's something like $50 a sheet and you have to get it from a QuietRock distributor. It works great and it's easy to install, it just costs a lot.
 
Wow.......I've been a wall and ceiling mechanic for 32yrs....and I'm confused.

Layering would be the cheapest easiest solution, although when I built my dedicated 2ch room I just built a room inside a room, braced the studs back to the existing wall and filled the cavity with Roxul batt......works well.....I did put sill gasket under the top and bottom plates, and used type X 5/8" D/W. Buffalo board (Tentest) isnt always easy to find, you could use acoustic ceilingtile.....look in your local buy sell for used, theyre cheap. I wouldnt worry about the screws transferring much if you isolate the plates with a gasket. Keep the drywall off the floor 1/2", you could caulk this space if you like with non hardening material.
Sometimes its better not to over think.....
 
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This site has tons of info [sure they are trying to sell things, but they have test results for most of the materials and sound proofing treatments]. http://www.acousticalsurfaces.com/

Several companies that do soundproofing use the equivalent of Dynamat on the studs anywhere they contact the drywall as well as between the drywall and hardboard. I wonder if self adhesive rubber edpm tape and rolls [roofing] would be similarly effective? I would also consider using silicone calk to seal every crack, every joint, and surface that could allow air movement. I would put it on the studs itself before screwing the drywall in place on the noise side of your new wall. OSI SC-175 Acoustical Sound Latex Sealant and some lead tape could help too. Using different thicknesses of drywall was recommended to prevent increasing the possible amount of resonance.

Take care,

Rob
 
I would also consider using silicone calk to seal every crack, every joint, and surface that could allow air movement. I would put it on the studs itself before screwing the drywall in place on the noise side of your new wall.
Sealing is very important, but it's really not necessary to caulk the gaps between wallboards. Regular mud and tape does just fine for that. Do use acoustical sealant around electrical boxes and pipe/wiring penetrations, though.
 
RevMen,
Do you know how these methods compare to mounting the GWB on a resilient channel that isolates it from the framing? I had read in a trade mag some time ago this was supposedly the simplest method to prevent sound transmission, and very effective.
 
RevMen,
Do you know how these methods compare to mounting the GWB on a resilient channel that isolates it from the framing? I had read in a trade mag some time ago this was supposedly the simplest method to prevent sound transmission, and very effective.
RC works well and is fairly inexpensive. It has to be installed before you mount drywall, though, so it's not a very good retrofit option.

And it must be installed correctly. We usually don't recommend RC because installers mess it up all the time. Sometimes they send screws right through the drywall into the studs, which defeats the entire purpose of having RC. Sometimes they install it upside down. Sometimes they allow it to become too compressed. And sometimes, the worst of all, they put the RC between layers of gypboard, which turns a wall into a big speaker with less TL than if the RC wasn't there.
 
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