A vehicle silencer works on the principle of destructive interference of sound waves. Inside the silencer, a set of tubes are designed to deliberately reflect sound waves originating from the engine. These reflected waves, interfere and cancel out each other.

In other parts of the world, i.e. not UK, the silencer is known as the muffler.

See link:

http://www.howstuffworks.com/muffler.htm

Turn down the volume

Turn off volume

silencer for what?, for a auto? for a gun?, for anything else? noise canceling?