Editing Microphone (section)

== Measurement microphones ==
<!--"Measurement microphone" redirects here.-->
[[File:AKG C214 condenser microphone with H85 shock mount.jpg|thumb|upright|An AKG C214 condenser microphone with [[shock mount]]]]

Some microphones are intended for testing speakers, measuring noise levels and otherwise quantifying an acoustic experience. These are calibrated transducers and are usually supplied with a calibration certificate that states absolute sensitivity against frequency. The quality of measurement microphones is often referred to using the designations "Class 1", "Type 2", etc., which are references not to microphone specifications but to [[sound level meter]]s.<ref>IEC Standard 61672 and ANSI S1.4</ref> A more comprehensive standard<ref>IEC 61094</ref> for the description of measurement microphone performance was recently adopted.

Measurement microphones are generally scalar sensors of [[pressure]]; they exhibit an omnidirectional response, limited only by the scattering profile of their physical dimensions. [[Sound intensity]] or sound power measurements require pressure-gradient measurements, which are typically made using arrays of at least two microphones, or with [[Hot-wire anemometry|hot-wire anemometers]].

===Calibration===
{{Main|Measurement microphone calibration}}

To take a scientific measurement with a microphone, its precise sensitivity must be known (in volts per [[Pascal (unit)|pascal]]). Since this may change over the lifetime of the device, it is necessary to regularly [[Calibration|calibrate]] measurement microphones. This service is offered by some microphone manufacturers and by independent certified testing labs. All [[measurement microphone calibration|microphone calibration]] is ultimately traceable to [[primary standard]]s at a national measurement institute such as [[National Physical Laboratory (United Kingdom)|NPL]] in the UK, [[Physikalisch-Technische Bundesanstalt|PTB]] in Germany and [[NIST]] in the United States, which most commonly calibrate using the reciprocity primary standard. Measurement microphones calibrated using this method can then be used to calibrate other microphones using comparison calibration techniques.

Depending on the application, measurement microphones must be tested periodically (every year or several months, typically) and after any potentially damaging event, such as being dropped (most such microphones come in foam-padded cases to reduce this risk) or exposed to sounds beyond the acceptable level.