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A hydrophone (Ancient Greek: ὕδωρ + φωνή, lit. 'water + sound') is a microphone designed for underwater use, for recording or listening to underwater sound. Most hydrophones contains a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a sound wave.
The Android software app, AquaApp, from University of Washington uses the microphones and speakers on existing smartphones and smart watches to enable underwater acoustic communication. [31] It had been tested to send digital messages using smartphones between divers at distances of up to 100 m.
A water microphone or water transmitter is based on Ohm's law that current in a wire varies inversely with the resistance of the circuit. The sound waves from a human voice cause a diaphragm to vibrate which causes a needle or rod to vibrate up and down in water that has been made conductive by a small amount of acid.
The first experimental array was a six-element test array laid at Eleuthera in the Bahamas in 1951, followed, after successful experiments with a target submarine, in 1952 by a fully-functional 1,000 ft (304.8 m), forty-hydrophone array. At that time the order for stations was increased from six to nine.
Astatic also manufactured bullet style microphones, which are extremely popular among harmonica players. The original Astatic model JT-30 was introduced in late 1939. There were many variations in different colors such as the JT-30-C, W-30, 31, JT-31, JT-40, JT-50, W40, W80 and Model A.
Shure Brothers microphone, model 55S, multi-impedance "Small Unidyne" dynamic from 1951. A microphone, colloquially called a mic (/ m aɪ k /), [1] or mike, [a] is a transducer that converts sound into an electrical signal.
The sensitivity of a microphone is usually expressed as the sound field strength in decibels (dB) relative to 1 V/Pa (Pa = N/m 2) or as the transfer factor in millivolts per pascal (mV/Pa) into an open circuit or into a 1 kiloohm load. [citation needed] The sensitivity of a hydrophone is usually expressed as dB relative to 1 V/μPa. [7]
Sound in water is measured using a hydrophone, which is the underwater equivalent of a microphone. A hydrophone measures pressure fluctuations, and these are usually converted to sound pressure level (SPL), which is a logarithmic measure of the mean square acoustic pressure. Measurements are usually reported in one of two forms:
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