A sound source radiates sound by causing local displacements to the surrounding medium. The amplitude of the radiated sound is related to the volume of air displaced by the source. For a simple sound source such as a moving piston or diaphragm, this volume is formed by the area of the radiating surface together with the extent of its displacement.

Sound sources are usually based on a vibrating surface that radiates sound energy into the surrounding medium. The type of sound field produced by the source depends on the source geometry, i.e. the shape and dimensions of the source, as well as possible surrounding structures. Following are typical three sources of sound.

Plane wave source

An ideal plane wave source consists of a pulsating rigid surface that is infinitesimally thin and has infinite length and width. The surface radiates sound energy equally to its front and back directions. A plane wave source produces a plane wave, which (in the ideal case) does not exhibit geometric attenuation with increasing distance from the source.

Line source

An ideal line source can be considered as a pulsating cylinder that is infinitesimally thin and has an infinite length. The cylinder emits sound energy equally to all radial directions. A line source produces a cylindrical sound field, where the sound pressure level attenuates by 3 dB for each doubling of distance from the source. A line source may be approximated by a line array of multiple point sources, such as dynamic loudspeaker elements.

Point source

An ideal point source can be considered as a pulsating sphere that is infinitesimally small in size. The sphere is omni-directional, i.e. sound energy is emitted equally to all directions. Due to geometrical attenuation, the sound pressure level is reduced by 6 dB for every doubled distance from the source.

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