Editing Parabolic microphone

{{Short description|Microphone that uses a parabolic reflector to collect and focus sound waves onto a transducer}}
{{Use British English|date=August 2024}}

[[File:ParabolicMicrophone.jpg|thumb|right|Parabolic microphone used at an American college football game.]] 

A '''parabolic microphone''' is a [[microphone]] that uses a [[parabolic reflector]] to collect and focus [[sound]] waves onto a [[transducer]], in much the same way that a [[parabolic antenna]] (e.g. [[satellite dish]]) does with [[radio wave]]s.  Though they lack high fidelity, parabolic microphones have great sensitivity to sounds coming from one direction, along the axis of the dish, and can pick up distant sounds.

[[File:Sony parabolic reflector.jpg|thumb|right|A Sony parabolic reflector, without a microphone. The microphone would face the reflector surface and sound captured by the reflector would bounce towards the microphone.]]

==Limitations==
Parabolic microphones are generally not used for [[high-fidelity]] applications because dishes small enough to be portable have poor low-frequency response. This is because, from the [[Angular resolution#The_Rayleigh_criterion|Rayleigh criterion]], parabolic dishes can only focus waves with a wavelength much smaller than the diameter of their aperture. The wavelength of sound waves at the low end of human hearing (20&nbsp;Hz) is about {{convert|17|metres|feet}}; focusing them would require a dish much larger than this. A typical parabolic microphone dish with a diameter of one metre has little [[directivity]] for sound waves longer than 30&nbsp;cm, corresponding to frequencies below 1&nbsp;kHz. For higher frequencies, a gain of about 15&nbsp;[[decibel|dB]] can be expected. But when the wavelength of the sound becomes comparable with the diameter of the parabolic dish, the response falls away.<ref name=S&R>{{cite book|last1=Rumsey|first1=Francis|last2=McCormick|first2=Tim|title=Sound and Recording|url=https://archive.org/details/soundrecording00rums|url-access=limited|date=2009|publisher=Elsevler Ltd.|location=Burlington, MA |isbn=978-0-240-52163-3|page= 60|edition=6}}</ref>

A [[shotgun microphone]], or a [[phased array]] of microphones, may be used as an alternative for applications requiring directional selectivity with high fidelity.

==Applications==
Typical uses of this microphone include nature [[sound recording]] such as recording [[bird call]]s, field audio for sports broadcasting, and [[eavesdropping]] on conversations, for example in [[espionage]] and law enforcement. Parabolic microphones were used in many parts of the world as early as World War II, especially by the Japanese.

Parabolic microphones are also used by [[search and rescue]] teams to locate lost people in wilderness environments. This application is supported by a study comparing parabolic microphones to unaided hearing in detecting and comprehending calling subjects at distances out to 2500 meters.<ref>{{cite journal |last1=Bowditch |first1=Nathaniel L. |last2=Searing |first2=Stanley K. |last3=Thomas |first3=Jeffrey A. |last4=Thompson |first4=Peggy K. |last5=Tubis |first5=Jacqueline N. |last6=Bowditch |first6=Sylvia P. |title=Use of a Parabolic Microphone to Detect Hidden Subjects in Search and Rescue |journal=Wilderness & Environmental Medicine |date=March 2018 |volume=29 |issue=1 |pages=11–17 |doi=10.1016/j.wem.2017.09.002|s2cid=4909984|doi-access=free |pmid=29311004 }}</ref>

==See also==
* [[Acoustic location]]
* [[Acoustic mirror]]

==References==
{{Reflist}}

[[Category:Microphones]]
[[Category:Surveillance]]
[[Category:Covert listening devices]]