A microphone, colloquially named mic or mike (/maɪk/),[1] is a device – a transducer – that
converts sound into an electrical signal. Microphones are used in many applications such
as telephones, hearing aids, public address systems for concert halls and public events, motion
picture production, live and recorded audio engineering, sound recording, two-way
radios, megaphones, radio and television broadcasting, and in computers for recording
voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic sensors or knock
sensors.
Several types of microphone are in use, which employ different methods to convert the air pressure
variations of a sound wave to an electrical signal. The most common are the dynamic microphone,
which uses a coil of wire suspended in a magnetic field; the condenser microphone, which uses the
vibrating diaphragm as a capacitor plate; and the piezoelectric microphone, which uses a crystal
of piezoelectric material. Microphones typically need to be connected to a preamplifier before the
signal can be recorded or reproduced.
Contents
1History
2Components
3Varieties
o 3.1Condenser
3.1.1Electret condenser
o 3.2Dynamic
o 3.3Ribbon
o 3.4Carbon
o 3.5Piezoelectric
o 3.6Fiber-optic
o 3.7Laser
o 3.8Liquid
o 3.9MEMS
o 3.10Speakers as microphones
4Capsule design and directivity
5Polar patterns
o 5.1Omnidirectional
o 5.2Unidirectional
o 5.3Cardioid, hypercardioid, supercardioid, subcardioid
o 5.4Bi-directional
o 5.5Shotgun
o 5.6Boundary or "PZM"
6Application-specific designs
7Stereo microphone techniques
8Powering
9Connectors
o 9.1Impedance-matching
o 9.2Digital microphone interface
10Measurements and specifications
11Measurement microphones
o 11.1Calibration
12Arrays
13Windscreens
14See also
15Further reading
16References
17External links
History[edit]
In order to speak to larger groups of people, a need arose to increase the volume of the human
voice. The earliest devices used to achieve this were acoustic megaphones. Some of the first
examples, from fifth century BC Greece, were theater masks with horn-shaped mouth openings that
acoustically amplified the voice of actors in amphitheatres.[2] In 1665, the English physicist Robert
Hooke was the first to experiment with a medium other than air with the invention of the "lovers'
telephone" made of stretched wire with a cup attached at each end.[3]
In 1861, German inventor Johann Philipp Reis built an early sound transmitter (the "Reis telephone")
that used a metallic strip attached to a vibrating membrane that would produce intermittent current.
Better results were achieved in 1876 with the "liquid transmitter" design in early telephones
from Alexander Graham Bell and Elisha Gray – the diaphragm was attached to a conductive rod in
an acid solution.[4] These systems, however, gave a very poor sound quality.
David Edward Hughes invented a carbon microphone in the 1870s.
The first microphone that enabled proper voice telephony was the (loose-contact) carbon
microphone. This was independently developed by David Edward Hughes in England and Emile
Berliner and Thomas Edison in the US. Although Edison was awarded the first patent (after a long
legal dispute) in mid-1877, Hughes had demonstrated his working device in front of many witnesses
some years earlier, and most historians credit him with its invention.[5][6][7][8] The carbon microphone is
the direct prototype of today's microphones and was critical in the development of telephony,
broadcasting and the recording industries.[9] Thomas Edison refined the carbon microphone into his
carbon-button transmitter of 1886.[7][10] This microphone was employed at the first ever radio
broadcast, a performance at the New York Metropolitan Opera House in 1910.[11][12]
Jack Brown interviews Humphrey Bogart and Lauren Bacall for broadcast to troops overseas during World War
II.
In 1916, E.C. Wente of Western Electric developed the next breakthrough with the first condenser
microphone.[13] In 1923, the first practical moving coil microphone was built. The Marconi-Sykes
magnetophone, developed by Captain H. J. Round, became the standard for BBC studios in
London.[14][15] This was improved in 1930 by Alan Blumlein and Herbert Holman who released the
HB1A and was the best standard of the day.[16]
Also in 1923, the ribbon microphone was introduced, another electromagnetic type, believed to have
been developed by Harry F. Olson, who essentially reverse-engineered a ribbon speaker.[17] Over the
years these microphones were developed by several companies, most notably RCA that made large
advancements in pattern control, to give the microphone directionality. With television and film
technology booming there was demand for high fidelity microphones and greater
directionality. Electro-Voice responded with their Academy Award-winning shotgun microphone in
1963.
During the second half of 20th century development advanced quickly with the Shure Brothers
bringing out the SM58 and SM57.[18] The latest research developments include the use of fibre optics,
lasers and interferometers.
Components[edit]
Electronic symbol for a microphone
The sensitive transducer element of a microphone is called its element or capsule. Sound is first
converted to mechanical motion by means of a diaphragm, the motion of which is then converted to
an electrical signal. A complete microphone also includes a housing, some means of bringing the
signal from the element to other equipment, and often an electronic circuit to adapt the output of the
capsule to the equipment being driven. A wireless microphone contains a radio transmitter.
Varieties[edit]
Microphones are categorized by their transducer principle, such as condenser, dynamic, etc., and by
their directional characteristics. Sometimes other characteristics such as diaphragm size, intended
use or orientation of the principal sound input to the principal axis (end- or side-address) of the
microphone are used to describe the microphone.
