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Old 08-04-2010, 08:22 AM   #1
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Soundproofing- fact or myth


Everything I read about soundproofing or every time an expert tells me about it it's always the same: Insulation does very little (if anything) to help sound proof.

On the other hand, every person I have ever talked to about insulating their house has always mentioned how much quieter it is afterwards. I see insulation added to interior walls between offices to limit sound on commercial jobs.

So what is it? Does insulation help or not?

I own a condo that used to be an apartment and it has no sound proofing at all, just typical stick built like a house. I was wondering if filling the joist space with blown in cellulose would help limit the noise from coming thru from the downstairs neighbor? I understand that it won't help with deep bass from the stereo or loud knocking, but will it help with talking and television noise?
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Old 08-04-2010, 08:51 AM   #2
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Sound insulation is a different material to thermal insulation.
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Old 08-04-2010, 09:47 AM   #3
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The way they insulate in music studios is to have two walls about 3" apart from each other with an air gap in between. I'm not sure if each wall is insulated, but there is not insulation between the walls.

They also make quietrock drywallthat apparently is like having 7-8 layers of normal sheetrock, and special acoustic insulation.
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Old 08-04-2010, 10:17 AM   #4
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My question is whether insulation does or does not help limit sound transmission.
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Old 08-04-2010, 10:54 AM   #5
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I would say yes. I just remodeled my bathroom, and I decided to put some fiberglass insulation in the interior walls for soundproofing purposes. Johns Manville insulation says "Thermal & acoustic" on it, FWIW.

As soon as I put the insulation up (before drywall) the room sounded dead when you spoke. It got a little more echo-ey when I drywalled, but I've gotta believe the insulation is helping with sound traveling between walls.
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Old 08-04-2010, 10:59 AM   #6
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Quote:
Originally Posted by secutanudu View Post
I would say yes. I just remodeled my bathroom, and I decided to put some fiberglass insulation in the interior walls for soundproofing purposes. Johns Manville insulation says "Thermal & acoustic" on it, FWIW.

As soon as I put the insulation up (before drywall) the room sounded dead when you spoke. It got a little more echo-ey when I drywalled, but I've gotta believe the insulation is helping with sound traveling between walls.
Yup, I hear that a lot. As I mentioned in my first post, insulation is added to the walls between individual offices in commercial work very often. Also, people who had their house insulated (cellulose blown into the outside walls) always say that it's quieter.

However, whenever reading about sound proofing or talking to a professional, they always say that insulation does very little if anything for limiting sound.

I was hoping a sound proofing pro would comment on that.
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Old 08-04-2010, 11:06 AM   #7
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I noticed even regular thermal insulation helps. You can never get 100% sound proof unless you get more complicated, but for general sound dampening it works.

When I was working in my attic and adding insulation, as I layered on, I started to not hear as much what was going on in the house. After 3 layers of R19, you can barely hear talking. I'm sure sound insulation works even better.
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Old 08-04-2010, 11:11 AM   #8
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Quote:
Originally Posted by Proby View Post
My question is whether insulation does or does not help limit sound transmission.
Of course insulation helps...as long as it is the right kind of insulation.

to insulate:

: to place in a detached situation : isolate; especially : to separate from conducting bodies by means of nonconductors so as to prevent transfer of electricity, heat, or sound

anything that prevents the transmission of vibrations (sound waves) will help. You also need to understand there are all sorts of means of transmission of sound through a building. Since there is sheetrock on both sides of a chunk of wood for a typical wall, you will always have sounds transmission but that would typically be in the lower freq's as a high freq would be attenuated by the mass itself. Wall rigidity and adding mass would improve that type of sound attenuation though.

the insulation helps prevent higher freq's as it dampens the air space between the two outside layers of sheetrock.

I have often seen insulation the insulation workers called gorilla hair or some such name. It was miserable to work with. It looked like really dense and dirty yellow fiberglass. Light fiberglass in not going to be as effective because it simply is not designed to prevent sound transmission. It will help but there are better means.

I believe the cellulose would be better for sound attenuation than something such as typical fiberglass insulation simply due to the density of the material. As you said, you will still have the situation with lower freq's but I think the cellulose might actually help some there though as well.
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Old 08-04-2010, 11:35 AM   #9
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I have often seen insulation the insulation workers called gorilla hair or some such name.
We call that stuff Rotten Cotton
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Old 08-04-2010, 10:28 PM   #10
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Sure it helps. Mineral wool is better than fiberglass; don't know about cellulose batts, but I'd bet they are better, too. Best thing? Acoustical insulation, of course. Any reason you can't install that? I just read here, for kicks. Of use?
http://en.wikipedia.org/wiki/Soundproofing
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Old 08-09-2010, 12:08 PM   #11
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Good question about insulation. Here are some general points:
  • Standard insulation is as good as the most expensive "acoustic" insulation.
  • Foam, whether a board or spray foam, is a poor acoustic material.
  • If compressed, insulation will conduct a vibration.
  • In a coupled wall, the insulation offers some assistance, but not a lot. Insulation offers a much bigger payback in a decoupled frame.
So insulation does a little, but not a lot, especially in a coupled wall (common wall). You would see better results adding a second sheet of drywall.
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Old 08-09-2010, 12:12 PM   #12
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Quote:
Originally Posted by secutanudu View Post
They also make quietrock drywallthat apparently is like having 7-8 layers of normal sheetrock.
That is a marketing sell point, as the assertion has never been verified in a lab. Actually in 11 years I have never even heard of an official explanation as to how that might be theoretically true.
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Old 08-09-2010, 12:19 PM   #13
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Quote:
Originally Posted by Ted White View Post
Good question about insulation. Here are some general points:
  • Standard insulation is as good as the most expensive "acoustic" insulation.
  • Foam, whether a board or spray foam, is a poor acoustic material.
  • If compressed, insulation will conduct a vibration.
  • In a coupled wall, the insulation offers some assistance, but not a lot. Insulation offers a much bigger payback in a decoupled frame.
So insulation does a little, but not a lot, especially in a coupled wall (common wall). You would see better results adding a second sheet of drywall.
Excellent I am glad to have a soundproofing professional reply.

What you say makes sense and stands to reason.

Will blown in cellulose insulation be a bit better than typical fiberglass batts?
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Old 08-09-2010, 12:22 PM   #14
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Independent tests done by the Canadian Government show that cheap fiberglass insulation is as good as it gets. However, similar density cellulose or mineral wool is fine also. The key is to not compress it.

If you tested scenario #1, inserting insulation in that wall or scenario #2, leaving the wall hollow and installing a second sheet of $6 drywall, scenerio #2 will win.
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Old 08-09-2010, 01:26 PM   #15
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About 30 years ago, we built a second home, and although we refer to it as "the cabin", it is very well constructed, including 2x6 exterior walls, etc. But, recognizing that all of the rooms were relatively small, and that we would use tile throughout, for ease of maintenance, I wanted to do something in regard to soundproofing. So, since there was less information available then, than there is today, I finally opted to insulate all of the interior walls with fiberglass insulation, and after using this home periodically, for 30 years, I can honsetly say that my firsthand experience is that it provides no advantage in regard to noise transfer. I have, however, noticed what I believe to be a downside, at least in our case, in which this home is not zoned, in that I believe that there are more warm and cold spots within the home, as the temperature is not able to balance as well. On the other hand, I have since seen other houses in which noise transfer is very good, and when I have inquired, it is where they have sonstructed two unattached walls, back-to-back.
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