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The term tonpilz or "acoustic mushroom" may refer to a certain type of underwater electro-acoustic transducer. By sandwiching active (i.e. piezoelectric or magnetostrictive) 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 (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. [1]

Typically, tonpilz transducers are used in sonar applications. To maximize efficiency, transducers are often placed in arrays: a grid of sometimes hundreds of transducers. This arrangement also allows beamforming and steering.

Transducers of this form also lend themselves to compensation against the hydrostatic pressures encountered in sonar, particularly for submarine applications. [2]

"Acoustic mushroom" may also refer to a passive ceiling or wall treatment applied to the insides of concert auditoria, including the Royal Albert Hall.

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Acoustics Branch of physics involving mechanical waves

Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Sonar Technique that uses sound propagation

Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used for robot navigation, and SODAR is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.

Ultrasound Sound waves with frequencies above the human hearing range

Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz in healthy young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.

A hydrophone 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 potential when subjected to a pressure change, such as a sound wave. Some piezoelectric transducers can also serve as a sound projector, but not all have this capability, and some may be destroyed if used in such a manner.

Echo sounding Measuring the depth of water by transmitting sound waves into water and timing the return

Echo sounding is a type of sonar used to determine the depth of water by transmitting sound waves into water. The time interval between emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time. This information is then typically used for navigation purposes or in order to obtain depths for charting purposes. Echo sounding can also refer to hydroacoustic "echo sounders" defined as active sound in water (sonar) used to study fish. Hydroacoustic assessments have traditionally employed mobile surveys from boats to evaluate fish biomass and spatial distributions. Conversely, fixed-location techniques use stationary transducers to monitor passing fish.

A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.

Bulbous bow part of a ship

A bulbous bow is a protruding bulb at the bow of a ship just below the waterline. The bulb modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency, and stability. Large ships with bulbous bows generally have twelve to fifteen percent better fuel efficiency than similar vessels without them. A bulbous bow also increases the buoyancy of the forward part and hence reduces the pitching of the ship to a small degree.

A scientific echosounder is a device which uses sonar technology for the measurement of underwater physical and biological components—this device is also known as scientific sonar. Applications include bathymetry, substrate classification, studies of aquatic vegetation, fish, and plankton, and differentation of water masses.

Sound from ultrasound is the name given here to the generation of audible sound from modulated ultrasound without using an active receiver. This happens when the modulated ultrasound passes through a nonlinear medium which acts, intentionally or unintentionally, as a demodulator.

Underwater acoustics The study of the propagation of sound in water and the interaction of sound waves with the water and its boundaries

Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly. Underwater acoustics is sometimes known as hydroacoustics.

Ultrasonic transducer Acoustic sensor

Ultrasonic transducers and ultrasonic sensors are devices that generate or sense ultrasound energy. They can be divided into three broad categories: transmitters, receivers and transceivers. Transmitters convert electrical signals into ultrasound, receivers convert ultrasound into electrical signals, and transceivers can both transmit and receive ultrasound.

Frederick Vinton Hunt Accoustical engineer

Frederick Vinton Hunt was an inventor, a scientist and a professor at Harvard University who worked in the field of acoustic engineering.

Salvage diving is the diving work associated with the recovery of all or part of ships, their cargoes, aircraft, and other vehicles and structures which have sunk or fallen into water. In the case of ships it may also refer to repair work done to make an abandoned or distressed but still floating vessel more suitable for towing or propulsion under its own power. The recreational/technical activity known as wreck diving is generally not considered salvage work, though some recovery of artifacts may be done by recreational divers.

Marine mammals and sonar

Active sonar, the transmission equipment used on some ships to assist with navigation, is detrimental to the health and livelihood of some marine animals. Research has recently shown that beaked and blue whales are sensitive to mid-frequency active sonar and move rapidly away from the source of the sonar, a response that disrupts their feeding and can cause mass strandings. Some marine animals, such as whales and dolphins, use echolocation or "biosonar" systems to locate predators and prey. It is conjectured that active sonar transmitters could confuse these animals and interfere with basic biological functions such as feeding and mating. The study has shown whales experience decompression sickness, a disease that forces nitrogen into gas bubbles in the tissues and is caused by rapid and prolonged surfacing. Although whales were originally thought to be immune to this disease, sonar has been implicated in causing behavioral changes that can lead to decompression sickness.

An underwater acoustic positioning system is a system for the tracking and navigation of underwater vehicles or divers by means of acoustic distance and/or direction measurements, and subsequent position triangulation. Underwater acoustic positioning systems are commonly used in a wide variety of underwater work, including oil and gas exploration, ocean sciences, salvage operations, marine archaeology, law enforcement and military activities.

Short baseline acoustic positioning system A class of underwater acoustic positioning systems used to track underwater vehicles and divers

A short baseline (SBL) acoustic positioning system is one of three broad classes of underwater acoustic positioning systems that are used to track underwater vehicles and divers. The other two classes are ultra short baseline systems (USBL) and long baseline systems (LBL). Like USBL systems, SBL systems do not require any seafloor mounted transponders or equipment and are thus suitable for tracking underwater targets from boats or ships that are either anchored or under way. However, unlike USBL systems, which offer a fixed accuracy, SBL positioning accuracy improves with transducer spacing. Thus, where space permits, such as when operating from larger vessels or a dock, the SBL system can achieve a precision and position robustness that is similar to that of sea floor mounted LBL systems, making the system suitable for high-accuracy survey work. When operating from a smaller vessel where transducer spacing is limited, the SBL system will exhibit reduced precision.

A Fessenden oscillator is an electro-acoustic transducer invented by Reginald Fessenden, with development starting in 1912 at the Submarine Signal Company of Boston. It was the first successful acoustical echo ranging device. Similar in operating principle to a dynamic voice coil loudspeaker, it was an early kind of transducer, capable of creating underwater sounds and of picking up their echoes.

Note: This page refers to the device used to measure the speed of sound in water for use in hydrography

Frank Massa American engineer

Frank Massa (1906–1990) was an American engineer who contributed greatly to the development of the field of acoustical engineering. He is perhaps best known for the development of recorded sound technology for the motion picture industry and, during World War II, the development of the first towed sonar transducers and hydrophones used by the U.S. Navy to detect and defeat German U-boat submarines.

Gordon Eugene Martin American physicist

Gordon Eugene Martin is a physicist and author in the field of piezoelectric materials for underwater sound transducers. He wrote early computer software automating iterative evaluation of direct computer models through a Jacobian matrix of complex numbers. His software enabled the Navy Electronics Laboratory (NEL) to accelerate design of sonar arrays for tracking Soviet Navy submarines during the Cold War.


  1. Wilson, O. B. (1988). Introduction to Theory and Design of Sonar Transducers. Peninsula Publishing.
  2. EP 0473480,"Electroacoustic transducer for use under water and comprising a system for automatically compensating the hydrostatic pressure"


Stansfield, D. (1991). Underwater Electroacoustic Transducers. Peninsula Publishing.