Soundproofing Forum Topics > Soundproofing your single family home from traffic noise and neighbors.

Impossible to soundproof bedroom wall??

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I'm trying to understand why all my efforts to soundproof a wall in our bedroom keep failing.

Here's the situation; Our north wall is 46ft long, 1 and half stories high (half the lower level is in the ground), no windows or doors. All our bedrooms and bathrooms run along the wall. Directly on the other side of this wall is our neighbors deck (about 5-6 feet away). When they're on the deck talking and yelling, we can hear them... all night

Originally, this wall had 5/8 drywall, 2x6 framing, fiberglass insulation, 1/2 osb, 1.5in Styrofoam, vinyl siding.

To start fixing this, I simply added a layer of 5/8 CertainTeed SilentFX drywall in our bedroom. The claim from them is that it "features a viscoelastic polymer between two specially formulated dense gypsum cores significantly improves sound attenuation and is ideal for systems requiring high STC performance." It was super heavy stuff. I installed it over the existing drywall with a gap all around the edges which I filled with acoustic sealant. This helped a little but we can still hear the neighbors talking and yelling.

I found out that the OSB  on this wall had a lot of rot due to the Styrofoam not being sealed. My thought was that the rotten OSB (lack of mass), was letting a lot of noise through, like an open door. Also, it seemed to me that Styrofoam can amplify sound (I can share some youtube video's to show what I mean). I tore down the outside of this wall, replaced all the OSB, sealed all cracks and gaps, then replaced the Styrofoam with Rockwool Comfortboard 80 (suppose to absorb sound). After doing all this... there was NO change in the amount of noise coming in. I was totally shocked.

Am I cursed? Or is there something else I've missed? Based on the STC rating of the drywall alone, I shouldn't be able to hear anyone talking normally. Yelling should be murmurs.

Randy S:
you did not follow Mass Law, and this is why you are not seeing the reduction you anticipated.

The other potential issue is that you do not have complex structure and therefore are stuck in Mass Law.

Give me a call direct and I will be happy to thoroughly explain this so you do not make another mistake.

Randy S.

Thanks for your reply but I'm not sure I follow. I found this

"The most important law in soundproofing is the mass law.The mass law equation says that each time the mass per unit area of a single layer wall is doubled, the transmission loss is increased by about 6 dB."

By adding the second layer of drywall, wouldn't I have been applying the "Mass Law"?

Randy S:
That is correct, unfortunately this is normal.
Standard 5/8" drywall weighs 2.3lbs sqft you have 1/2" OSB 1.7 lbs sqft on the other side plus what ever the siding weight is. = 4 lbs sqft.

you added Silent FX is 2.8 lbs sqft. you did not double the mass.

now, doubling the mass does not always give you desired results depending on the source, most projects I find myself at a minimum 8-9 lbs sqft just for low performing systems.
satisfactory systems are 10-12lbs sqft.

Now any bass or impact will still be able to come through unobstructed due to the single frame construction.

Randy S.

Thanks a lot for the extra information. Looks like I would need at least another 2 sheets of drywall. If I suggest that to the wife she would probably kill me so I'll just have to live with what we have.  :)

Thanks again.


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