MadSci Network: Physics

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


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

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 

Kind regards,


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