The Internet is full of myths, rumors and legends about many subjects, including soundproofing. Allow me to present three examples of misconceptions how to soundproof a room. Soundproofing a room should not be based on Internet rumors, but on solid scientific evidence.
Soundproofing a door with Styrofoam
The idea of nailing Styrofoam insulation to a light-weight door is complete nonsense. Furthermore, a display of a reputable brand is not a guarantee of reputability. Foam insulation has negligible effect on sound transmission (see reference ) and does not help to soundproof a room. In any case, gaps around the door are major pathway for noise and unless sealed, will negate any improvement made to the door itself .
On the other hand, the video below provides some good advice about installing a soundproof door, thus contributing to soundproofing a room.
Soundproofing a room with foam on walls
I have heard this myth many times. Presumably, you can soundproof a room by putting foam on the walls. The person in the next video presents (with authority!) how to soundproof a room. The problem is, however, that the advice is basically wrong.
The foam will reduce reverberation in the room somewhat, but only at high frequencies, because the layer of the foam is thin . The proposed method of nailing pieces of foam (even foam called “acoustic”) on the wall does not work for soundproofing a room, as explained in .
Soundproof a room with egg cartons
This seems to be a myth widely circulated on the Internet. While I was not able to find a source for the original myth, I found many stories disproving the myths. While some of them are really a myth about a myth, this one is accurate:
Not everyone is interested in a scientific explanation of why egg cartons do not work as soundproofing, or as sound diffusers, but the answer is clear. They do not help to soundproof a room.
As a contrary and mostly accurate example of improving acoustics in a listening room, see this video:
The presentation shows a comprehensive, if not somewhat extreme treatment of a listening room for multi-channel sound reproduction. But even this video propagates a myth. It shows that you can eliminate sound reflections from a coffee table by covering it with a towel. This will have a limited, if any effect on sound reflections, because the towel is thin .
In general, this video is interesting. It discusses many aspects of listening room acoustics that are actually debatable. I will articulate my view on this subject in a future article in this blog.
There is lot of information on the Internet about soundproofing a room, noise control and room acoustics. As demonstrated in the three simple examples above, a lot of the information is inaccurate, incomplete, unsuitable for the intended use, or just plain wrong. Each homeowner or contractor contemplating a soundproofing project should seriously consider hiring a soundproofing consultant. This advice applies particularly to those who think they have figured it out by themselves with the help of the Internet. Small amount of knowledge picked-up from the internet can sometimes lead to expensive errors. For an example of such an errors, see the article "A Case of Botched Office Reno."
 Master Handbook of Acoustics, Sixth Edition (2015) by Everest & Pohlmann (McGraw Hill Education), page 324
 Same, page 339
 Same, page 195
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