Soundproofing 'Inside out wall' compared to single stud wall

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Soundproofing 'Inside out wall' compared to single stud wall

Postby wim » Wed Sep 30, 2009 1:57 am

Hi all,

I've read posts about how single stud walls (ie standard wall, no staggers or anything) basically don't depend on thickness in terms of soundproofing. Doesn't really matter if you use 2x4's, or bigger or smaller, the acoustic shortcut of the studs negates the advantages of a bigger cavity.

Which made me think: what if the studs are only plated on one side? I believe that was called an 'inside out wall'? The question: when building a simple wall with 2x4 studs, is there a difference between studs with one layer of gypsum on both sides, and 2 layers of gypsum on one side with the other side unplated?

Reason I'm asking: adjacent to the music room (finally decided on staggered stud w/ green glue) are two small rooms, a kitchen and an engine room for among others the ventilation unit. The kitchen and the engine room will be separated from eachother by this simple wall. Due to cramped space, it would be nice to use an inside out wall. Feels a bit roomier, but I am worried about keeping the fan noise out of the kitchen.

These are the noise specs from the datasheet of the ventilation unit, in its highest setting:

125Hz - 62 db
250Hz - 62 dB
500Hz - 62dB
1000Hz - 51 dB
2000Hz - 45 dB
4000Hz - 36 dB
8000Hz - 25 dB

Possible to keep this noise out, with such a wall?

Thanks for any advice!
Wim
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Re: Soundproofing 'Inside out wall' compared to single stud wall

Postby Rod Gervais » Wed Sep 30, 2009 7:40 pm

Wim,

you misunderstand the concept of the inside out wall construction.

The construction you refer to is actually a double wall frame - but the drywall is installed on the inside face of the 2nd wall instead of the room side. In this manner the exposed stud cavity is able to become a concealed part of the room treatments as opposed to placing those treatments exposed in the rooom itself.

Asuming equal depth air spaces - a double wall frame would have exactly the same isolation value in either configuration.

Now - to go back to your original question - I do not recall ever seeing tests performed on a wall frame with the face on only one surface..... but I can tell you with some certainty that placing 2 layers of drywall on one face of a wall will not perform as well as placing them on opposite sides of the frame (assuming equal mass in both conditions).

This is due to the fact that the inside of the wall cavity creates an air spring when drywall is applied to both sides - and this adds to the isolation value of the assembly as a whole - you would loose this gain by placing the mass on only one wall side.

Rod
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Re: Soundproofing 'Inside out wall' compared to single stud wall

Postby wim » Sun Oct 04, 2009 12:23 am

Rod,

Thanks for the reply. I indeed goofed up the 'inside out wall' term :D

I'd probably need to put the noise figures for the ventilation box against the threshold of human hearing, and then check if the difference between the two is somewhat close to the wall attenuation, correct?

If that's OK, the problem is that I'm finding conflicting data on the web for the human threshold. When looking at 125 Hz data, one graph I found gives 25 dB threshold, and another 35 dB. The box is mostly LF and produces 62 dB at 125 Hz, thus either 37 or 27 dB attenuation is needed - quite a difference.

From experience, any tips on the simplest way to to keep this noise out?
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Re: Soundproofing 'Inside out wall' compared to single stud wall

Postby Terry Montlick » Sun Oct 04, 2009 12:48 pm

wim wrote:...
If that's OK, the problem is that I'm finding conflicting data on the web for the human threshold. When looking at 125 Hz data, one graph I found gives 25 dB threshold, and another 35 dB. The box is mostly LF and produces 62 dB at 125 Hz, thus either 37 or 27 dB attenuation is needed - quite a difference.

The "bible" of loudness psychoacoustics, Fletcher and Munson's famous paper of 1933, puts the 125 Hz hearing threshold at about 35 dB. More modern measurements, made in 1956, found this to be at around 20 dB. It has remained there right up through the most recent revision of ISO 226, "International Standards for Equal-Loudness Level Contours," in 2003.

- Terry
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Re: Soundproofing 'Inside out wall' compared to single stud wall

Postby wim » Thu Oct 08, 2009 12:10 am

I just tried to calculate the transmission loss of a 20 kg/m2 solid mass, which should be indicative of such a single-plated wall, and ended up with 20dB at 125 Hz. Clearly not enough... A double plated-wall it is then.

However, this does get me worried about another leak: above the ventilation unit is the living room. De floor between the two is 22 kg/m2. It's almost impossible to close the ceiling above the unit (4 big ducts enter the ceiling from the device, in a tight space). So I can't make a double leaf here.

Would it help a bit to stuff the ceiling space (30 cm) with rockwool? Any other ideas?
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Re: Soundproofing 'Inside out wall' compared to single stud wall

Postby jennyfan » Mon Mar 29, 2010 4:12 pm

I'm trying to find out the correct inside out wall construction on my unit. So, that is a good resource for guiding me on starting my project.
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Re: Soundproofing 'Inside out wall' compared to single stud wall

Postby gellergeorge » Mon Jun 28, 2010 8:41 am

I’d recommend QuietRock for anything related to soundproofing!
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