MadSci Network: Physics Query:

### Re: How does one deaden sound through walls?

Date: Fri Jan 19 09:25:16 2001
Posted By: Bruno Putzeys, Staff, Electroacoustics and Analog Electronics, Philips ITCL
Area of science: Physics
ID: 979056279.Ph
Message:
```
Hello,

There are 2 main ways in which sound can make its way from one room into
another:

1. Airborne. Through leaks (around doors, windows, air ducts). This is the
main cause of sound leakage and is often underestimated. Have gaskets
around doors and windows. Air ducts are tougher. Unless you can
periodically close it, the duct should have a padded labyrinth in it - not
something you can do in an existing building

2. Structure-borne. This means sound hitting a wall causing the wall to
vibrate (i.e. a sound wave within the solid structure). Sound waves
propagate much easier through solids than through air, which explains why
sounds inside some buildings can be heard many floors up or down from the
source. What decreases the sound level is the percentage of acoustic
energy that makes it across boundary between media (air and solid). The
larger the difference in mass between the media, the more difficult it
will be for a sound wave to enter from one medium into another. Simply
put: the heavier the wall, the better it will stop sound. As you can also
see from the above reasoning it is more effective to have more than 1
transition, as energy is lost every time. This can be done using a double
wall (optionally with padding in-between). Of course, the walls normally
share a common base (all solid) through which some of the sound will still
penetrate. If you really want this degree of isolation, a "room within a
room" sitting on springs is the ideal solution. A somewhat expensive and
impractical one.

In case of the glass wall, use two or three medium-thickness (0.2") sheets
of glass with air spacing (0.4" to 2")between them. Make sure no humidity
gets in-between there (nothing to do with the sound of course).
Alternatively, use 2 double-glass windows fitted to either side of the
wall.

Kind regards,

Bruno

```

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