6.3 Can you focus sound ?
Description
This article is from the Acoustics FAQ, by Andrew Silverman with numerous contributions by others.
6.3 Can you focus sound ?
Sound can be focused like light, but in the case of sound the "optics" must be much larger because you are dealing with longer wavelengths. The effect is heard in some domed buildings such as the Capitol in Washington, and St Paul's Cathedral in London providing noise background conditions permit.
Large parabolic reflectors can be used very effectively to send and receive sound over significant distances. Check out your local science museum or exploratorium - there may be a demonstration. It is also possible to refract sound and focus it using a lens. The lens is constructed from a large thin bubble, say 2 metres across, filled with carbon dioxide. The effect is not very pronounced.
Sound can be directed by making use of constructive and destructive interference. This idea is used in column speakers, and commercial systems for reducing noise levels outside the dance floor area of discos.
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