Room Acoustics Forum by Rives Audio

RE: Quick question

124.187.9.153

In Reply to: RE: Quick question posted by Toology86@yahoo.com on June 01, 2008 at 16:46:03

It won't affect the quality of sound in your room, but it will affect the passage of sound from your room to the attic if it's in the ceiling cavity between your room and the attic.

To have an effect upon sound in your room, acoustic treatments/insulation have to be "in contact" with sound in the room. They only affect sound that falls upon them, they don't "act at a distance". Effectively once sound passes through your drywall it isn't coming back. When sound strikes the drywall some of it is reflected and remains in the room. The rest passes into the drywall where some of it is absorbed and some of it eventually exits into the space behind the drywall. Theoretically a little of what passes through could be reflected back from the next surface behind the drywall and actually pass back through the drywall again but in practical terms that's ignorable since only a proportion of what passes through the first time (itself only a proportion of the original sound) will be reflected back and some of that back reflection will be reflected into the cavity again, some will be absorbed by the drywall as it passes through, and some will actually get back through the drywall to re-enter the room. As you can see from that description of what happens to sound passing through the drywall, the amount returning is going to be very low in comparison to what managed to pass through in the first place.

So, any insulation in the space behind the drywall will certainly absorb some of the sound passing through the drywall and reduce the possibility of any sound which gets through the drywall being reflected back to pass through the wall again and return into the room, but very little would have returned anyway so the impact of insulation behind the drywall on sound inside your room can basically be ignored as negligible.

David Aiken

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