The term tonpilz or "acoustic mushroom" may refer to a certain type of underwater electro-acoustic transducer. By sandwiching active (i.e.

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied Stress (mechanics), mechanical s ...

magnetostrictive Magnetostriction (cf. electrostriction) is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field chan ...

) materials between a light, stiff radiating head mass and a heavy tail mass, the transducer can effectively operate as either a projector (source) or a

hydrophone A hydrophone ( grc, ὕδωρ + φωνή, , water + sound) is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potenti ...

(underwater acoustic receiver). The transducer's size, odd shape, and acoustic projection capabilities have earned it the moniker "tonpilz", from the German words ''Ton'' (tone) and ''Pilz'' (mushroom) and from the figurative similarity. Typically, tonpilz transducers are used in

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect o ...

applications. To maximize efficiency, transducers are often placed in arrays: a grid of sometimes hundreds of transducers. This arrangement also allows

beamforming Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles e ...

and steering. Transducers of this form also lend themselves to compensation against the hydrostatic pressures encountered in sonar, particularly for submarine applications. "Acoustic mushroom" may also refer to a passive ceiling or wall treatment applied to the insides of concert auditoria, such as the

Royal Albert Hall The Royal Albert Hall is a concert hall on the northern edge of South Kensington, London. One of the UK's most treasured and distinctive buildings, it is held in trust for the nation and managed by a registered charity which receives no govern ...

References

Bibliography

{{cite book, first1=D. , last1=Stansfield, title=Underwater Electroacoustic Transducers, publisher=Peninsula Publishing, year= 1991 Sonar