Acoustic Anechoic Chambers
Anechoic chambers are commonly used in acoustics to conduct experiments in nominally "free field" conditions. All sound energy will be traveling away from the source with almost none reflected back. Common anechoic chamber experiments include measuring the transfer function of a loudspeaker or the directivity of noise radiation from industrial machinery. In general, the interior of an anechoic chamber is very quiet, with typical noise levels in the 10–20 dBA range. According to Guinness World Records, 2005, Orfield Laboratory's NIST certified Eckel Industries-designed anechoic chamber is "The quietest place on earth" measured at −9.4 dBA. The human ear can typically detect sounds above 0 dBA, so a human in such a chamber would perceive the surroundings as devoid of sound.
The University of Salford has a number of Anechoic chambers, of which one is unofficially the quietest in the world with a measurement of −12.4 dBA.
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