What is an inner wall?

What the data says is that the introduction of a small air cavity is a liability. See their exhaustive study "Control of Sound Transmission through Gypsum Board Walls." It's online and a good read. http://irc.nrc-cnrc.gc.ca/pubs/ctus/1_e.html

Also here: http://irc.nrc-cnrc.gc.ca/pubs/bsi/85-3_e.html

Some of these findings are perhaps counter-intuitive.

Posted by: JamesW at July 28, 2008 10:08 AM in response to Soundproofing Question

The insulation in the small airspace does not remove the liability. Lab tests confirm this. If you can't have a gap bigger than 2", leave no gap.

Good question about the cement board. In this case, mass is mass, so generally the cheapest source is most practical. That's why 5/8" drywall is so effective. Cheap, easy to use and heavy.

The "proprietary" boards like quiet rock and supress use a damping compound inside two sheets of standard 1/4" drywall or cement board. Build your own with green glue, save the $$ and have a heavier, more thoroughly damped wall as a result.

Posted by: JamesW at July 26, 2008 10:36 AM in response to Soundproofing Question

The NRC in Canada did a lot of great research into many odd areas. One great study involved looking at airspaces. The net of the study was that a small airspace introduced made things a lot worse at some frequencies. If you're going to introduce an airspace, make it big or do none at all.

Posted by: JamesW at July 24, 2008 8:11 PM in response to Soundproofing Question

Closed cell foam on studs is a pretty bad idea. First, as a decoupling material it is far too stiff. Along the lines of soundboard, which isn't saying a lot. Offsetting studs or using resilient clips or channel on the studs is a great idea.

Closed cell foam doesn't decouple well, and by virtue of the closed cell nature, is a poor material choice for sound absorption. This has been well documented by the NRC in Canada.

Posted by: JamesW at July 24, 2008 12:25 PM in response to Party wall soundproofing

When you're beefing up just one wall, you run the distinct risk that sound will find another route around that one wall (or ceiling). This is called flanking.

Flanking varies on a case by case basis based on construction. Sometimes treating one surface works well, and other times if there's too many flanking pathways it just doesn't.

Your situation looks way too open, and I would think treating that one wall would not work as well as you hope.

Regarding some of the other thoughts posted:

Quiet Rock and Supress are tremendously expensive relative to performance.

Green Glue is much less expensive relative to performance. "Guest" has posted that it is 50 year caulk, which is a foolish assertion. Green Glue is in the same family of visco-elastic materials as whant is inside Quiet Rock and Supress Board.

You want to avoid introducing a small air cavity in your efforts. Installing clips and channel as Steve suggested works if applied directly to the stud or joist. If you apply these to the existing dywall surface, you'll trap a small pocket of air that will act as an amplifier. These channels are generally 20,22 or 25 ga, steel. And Steve is right on about the misplaced screw negating much of the benefit.

Posted by: JamesW at July 24, 2008 8:56 AM in response to Soundproofing Question

The air cavity is to decouple one wall from another. The air space works like a shock absorber. The conversion of acoustic energy from structural to airborne and back to structural is one of the things that helps burn its energy. It's the same principle behind a double wall or a recording studio's double/triple glass (as opposed to double glazed) windows.

The inner wall should be relatively heavy because the more mass the energy has to move the more it depletes its energy -- at least one layer of Type X although I've mostly used two layers laminated with construction adhesive.

In any event, it's an impractical solution for an apartment, especially if there's wiring in the existing wall.

Posted by: Steve at July 24, 2008 1:37 PM in response to Soundproofing Question

The NRC in Canada did a lot of great research into many odd areas. One great study involved looking at airspaces. The net of the study was that a small airspace introduced made things a lot worse at some frequencies. If you're going to introduce an airspace, make it big or do none at all.

Posted by: JamesW at July 24, 2008 8:11 PM in response to Soundproofing Question

That's why I suggested stuffing with insulation, not for mass but to reduce the airborne transmission of sound.

As far as massing is considered, I wonder whether 2 layers cement board which is cheap and heavy would be as good as the more expensive proprietary boards. Of course you want structural integrity too, or the entire heavy wall will act as a diaphragm.

Posted by: cmu at July 25, 2008 11:06 AM in response to Soundproofing Question

Some studios line the walls with lead sheets made for the radiology industry. I dunno what the building codes are for that would be though.

Posted by: Steve at July 25, 2008 12:46 PM in response to Soundproofing Question

The insulation in the small airspace does not remove the liability. Lab tests confirm this. If you can't have a gap bigger than 2", leave no gap.

Good question about the cement board. In this case, mass is mass, so generally the cheapest source is most practical. That's why 5/8" drywall is so effective. Cheap, easy to use and heavy.

The "proprietary" boards like quiet rock and supress use a damping compound inside two sheets of standard 1/4" drywall or cement board. Build your own with green glue, save the $$ and have a heavier, more thoroughly damped wall as a result.

Posted by: JamesW at July 26, 2008 10:36 AM in response to Soundproofing Question

In other words, your contention is that no inner wall works as well as one with only a 2" air gap?

Posted by: Steve at July 27, 2008 5:13 PM in response to Soundproofing Question

What is an inner wall?

What the data says is that the introduction of a small air cavity is a liability. See their exhaustive study "Control of Sound Transmission through Gypsum Board Walls." It's online and a good read. http://irc.nrc-cnrc.gc.ca/pubs/ctus/1_e.html

Also here: http://irc.nrc-cnrc.gc.ca/pubs/bsi/85-3_e.html

Some of these findings are perhaps counter-intuitive.

Posted by: JamesW at July 28, 2008 10:08 AM in response to Soundproofing Question

I have a terraced house in London. On one side I have a party wall that joins next door's hall and kitchen.
When they were talking in the kitchen I could hear every word they were saying and when they used pots and banged things down it was as if it was in my house-it was that loud and clear.
The walls are nine inch brick with plaster on top.
I stuck plasterboard with green glue directly onto the wall.
I then stuck another layer of green glue and plastboard onto that.
I then used resilient bars and put another two sheets of plasterboard with green glue between them on top of that.
Now I can hardly hear anything at all except when they bang things down in the kitchen I can hear the impact noise, although it is somewhat muffled.
The green glue took several months to cure-it fact it still seems to be improving over a year later, possibly because the number of layers I've used has stopped it from drying.

Posted by: Herbert Smith at August 18, 2008 4:00 PM in response to Soundproofing Question

Herbert,
It looks to me that you built a triple leaf wall and that is why you think that the Green Glue is taking a year to cure. It probably cured within the first 30 days, but when you added the resilient channel over the first layers and then put more layers on top of that you created a small air pocket and that is why you can still hear some of those sounds. If you could open up your wall and take out those "resilient bars" you would have a better performing wall.

Posted by: SPC at October 21, 2008 3:51 PM in response to Soundproofing Question