Soundproofing a wall

Fred Willis

New member
Jan 1, 2023
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washington DC USSA
It's a stud wall, 5 1/2 inch studs between townhouse units, I'm gonna take off the drywall and put 1 1/4, maybe it's 1 3/4 MDF and pieces of 1 3/4 solid core doors between the studs ( I work at a door company). I think the question is I would expect to want to fit the MDF between the studs as good as possible. That might not be what I want to do. I might want to leave an 1/8 or 1/4 gap and fill that with acoustic caulk. Green glue on the side of the MDF facing the other unit. Any other suggestions for improvements? The drywall will go back onto the stud, use green glue there I'd think.
 
Any other suggestions for improvements?
Hire a qualified acoustical consultant to provide construction details.

From your post, it sound like you are trying to increase isolation between spaces. To do this, you need to eliminate paths for sound to travel between those spaces. This is normally done by a combination of eliminating air paths, eliminating vibration paths, and adding attenuation (absorption) to the paths that remain. There's also things like local building codes and fire codes that need to be respected, especially since it appears you're working on the wall between units.

For commercial office buildings, it's pretty common to see interior walls filled with fiberglass insulation to increase the sound isolation between adjacent rooms, but there are certainly other techniques that are also used where high isolation is required.
 
Oct 25, 2018
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Bideford, Devon. UK
Even if you can build an isolating wall, you must consider flanking (structure-borne) noise first as this is very difficult to treat and can negate any wall improvements particularly regarding impact noise. As Rob suggests, it's not as simple as adding a bit of mass and there is very good information online showing attenuation values of different constructions, which can often be counter intuitive! Although thick wood feels like a lot of mass it is trifling compared with masonry construction - my 17C stone walls are up to 200lb/sq.ft - so absorption and depth of lightweight walls becomes a critical design factor.
 

Paul Johnson

Freshman
Oct 27, 2012
113
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18
You've not said what the purpose of the project is? Stopping people next door's voices being recorded, or stopping your drum kit getting through to them, or what? Many architect designed between property solutions are pretty much limited to preventing speech. Depending on the floor and ceiling, a new panel with an air gap on a fairly lightweight stud system could work for some things, but MDF is a favourite of mine because it is pretty effective, string and can be easily fixed. It's heavy though, if that matters? I'm absolutely NOT a green glue fan, and depending on what you are trying to reduce, the sheet material could be thickened to produce a much cheaper reduction in transmission. What are you trying to cure?
 

Fred Willis

New member
Jan 1, 2023
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washington DC USSA
the purpose of the project is sound attenuation. I don't think you can have a one way soundproof wall like a one way mirror. My options are removing the drywall, doing something, and replacing the drywall. I have a ton of MDF.
 

Tim McCulloch

Graduate Student
Jan 11, 2011
3,068
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Wichita KS USA
the purpose of the project is sound attenuation. I don't think you can have a one way soundproof wall like a one way mirror. My options are removing the drywall, doing something, and replacing the drywall. I have a ton of MDF.
Adding mass is only part of vibration isolation and creating STL (sound transmission loss).

If you don't want to spend the $40 on the book, go to your library. SERIOUSLY.

Also adding flammable materials between residence units may be a violation of Code in your city or county, and may violate condo/home owner association rules. Check before you wreck!
 

Fred Willis

New member
Jan 1, 2023
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washington DC USSA
that book looks more suited for someone who owns a company that designs and builds recording studios. not even someone building a recording studio, someone who owns a company and builds studios, plural.
 
Oct 25, 2018
148
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Bideford, Devon. UK
the purpose of the project is sound attenuation. I don't think you can have a one way soundproof wall like a one way mirror. My options are removing the drywall, doing something, and replacing the drywall. I have a ton of MDF.
Mass is better than nothing, but you will be disappointed with simply plugging up the gaps with solid wood. Mass Law states that attenuation is only approximately 5db for every doubling of wall mass for a single skin wall. Any partition wall with a mechanical link (eg. plasterboard nailed each side of common studs) will be difficult to improve, and an entirely separate wall loosely coupled only to the side walls, floor, and ceiling only should be considered a minimum first step. You can then add as many layers of MDF as you like to your new wall (perhaps with the final layer on resilient bar) and partially fill the void with Rockwool - there must be an air gap with between it and the existing wall. Mechanical isolation is paramount! This construction can typically achieve about 55dB overall noise reduction.
 
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that book looks more suited for someone who owns a company that designs and builds recording studios. not even someone building a recording studio, someone who owns a company and builds studios, plural.
There are also reference books more specialized to the topic of reducing sound and vibration transmission - some of the works of Leo Beranek come to mind.
 
Oct 25, 2018
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Bideford, Devon. UK
Jan-reThink-10.jpg
 

Tim McCulloch

Graduate Student
Jan 11, 2011
3,068
57
48
Wichita KS USA
that book looks more suited for someone who owns a company that designs and builds recording studios. not even someone building a recording studio, someone who owns a company and builds studios, plural.
No, it's not. It's big on physics and the why's and how's of acoustics, noise transmission, etc so the principles apply regardless of the trade, craft, or profession of the user. It's a $40 book that will give you a lifetime of knowledge. It's free to check out at your local library. The only loss will be the ignorance you are maintaining.
 
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Chris Hindle

Freshman
Apr 18, 2011
109
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Montreal
that book looks more suited for someone who owns a company that designs and builds recording studios. not even someone building a recording studio, someone who owns a company and builds studios, plural.
I've had that book since the mid 80's, and I still crack it open from time to time....... Looong after the project I bought it for.
Knowledge is power. Studying the book is far cheaper than tearing out screwed up renovations.
 

Paul Johnson

Freshman
Oct 27, 2012
113
11
18
Fred - you still provided no details? What do you wish to do - attenuation is obvious, but what? Can you hear people speaking, or are worried they can hear you, or is it that you are a budding opera singer and don't wish to annoy neighbours, or do you not like the next door neighbours home cinema and you can hear the sub bass, through the wall - or the guy next door is learning the drums? Each of these scenarios requires a different approach. You seem to be reluctant to give us any details - clearly, the comment about the recording studio focus suggests it is not music you wish to attenuate. I did one once where there were benches bolted to a clockwork wall, and they were being used by welders - the benches were where they knocked off the slag. The hammer blows were amazingly loud. Very different from stopping a drum kit being heard.