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ARTICLES IN THE BOOK

  1. Acoustics
  2. AKG Acoustics
  3. Audio feedback
  4. Audio level compression
  5. Audio quality measurement
  6. Audio-Technica
  7. Balanced audio connector
  8. Beyerdynamic
  9. Blumlein Pair
  10. Capacitor
  11. Carbon microphone
  12. Clipping
  13. Contact microphone
  14. Crosstalk measurement
  15. DB
  16. Decibel
  17. Directional microphone
  18. Dynamic range
  19. Earthworks
  20. Electret microphone
  21. Electrical impedance
  22. Electro-Voice
  23. Equal-loudness contour
  24. Frequency response
  25. Georg Neumann
  26. Harmonic distortion
  27. Headroom
  28. ITU-R 468 noise weighting
  29. Jecklin Disk
  30. Laser microphone
  31. Lavalier microphone
  32. Loudspeaker
  33. M-Audio
  34. Microphone
  35. Microphone array
  36. Microphone practice
  37. Microphone stand
  38. Microphonics
  39. Nevaton
  40. Noise
  41. Noise health effects
  42. Nominal impedance
  43. NOS stereo technique
  44. ORTF stereo technique
  45. Parabolic microphone
  46. Peak signal-to-noise ratio
  47. Phantom power
  48. Pop filter
  49. Positive feedback
  50. Rode
  51. Ribbon microphone
  52. Schoeps
  53. Sennheiser
  54. Shock mount
  55. Shure
  56. Shure SM58
  57. Signal-to-noise ratio
  58. Soundfield microphone
  59. Sound level meter
  60. Sound pressure
  61. Sound pressure level
  62. Total harmonic distortion
  63. U 47
  64. Wireless microphone
  65. XLR connector

 

 



MICROPHONES
This article is from:
http://en.wikipedia.org/wiki/Electret_microphone

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Electret microphone

From Wikipedia, the free encyclopedia

 
Electret condenser microphone capsules
Electret condenser microphone capsules
A typical electret microphone preamp circuit uses an FET in a common source configuration.  The two-terminal electret capsule contains an FET which must be externally powered by supply voltage V+.  The resistor sets the gain and output impedance.  The audio signal appears at the output, after a DC-blocking capacitor.
A typical electret microphone preamp circuit uses an FET in a common source configuration. The two-terminal electret capsule contains an FET which must be externally powered by supply voltage V+. The resistor sets the gain and output impedance. The audio signal appears at the output, after a DC-blocking capacitor.

An electret microphone is a relatively new type of condenser microphone, which eliminates the need for a high-voltage bias supply by using a permanently-charged material.

An electret is a stable dielectric material with a permanently-embedded static electric charge (which, due to the high resistance of the material, will not decay for hundreds of years). The name comes from electrostatic and magnet; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron.

Electret materials have existed since the 1920s, and were proposed as condenser microphone elements several times, but were considered impractical until the foil electret type was invented at Bell laboratories in 1962 by Gerhard Sessler and Jim West, using a thin metallized Teflon foil.[1] This became the most common type, used in many applications from high-quality recording and lavalier use to built-in microphones in small sound recording devices and telephones.

Though electret mics were once considered low-cost and low quality, the best ones can now rival capacitor mics in every respect apart from low noise and can even have the long-term stability and ultra-flat response needed for a measuring microphone. There are three major types of microphone, depending on the way the electret material is used:

Foil-type or diaphragm-type 
A film of electret material is used as the diaphragm itself. This is the most common type, but also the lowest quality, since the electret material doesn't make a very good diaphragm.
Back electret 
An electret film is applied to the back plate of the microphone capsule and the diaphragm is made of a superior, uncharged material.
Front electret 
In this newer type, the back plate is eliminated from the design, and the condenser is formed by the diaphragm and the inside surface of the capsule. The electret film is adhered to the inside front cover and the metalized diaphragm is connected to the input of the FET.

Unlike other condenser microphones they require no polarising voltage, but normally contain an integrated preamplifier which does require power (often incorrectly called polarizing power or bias). This preamp is frequently phantom powered in sound reinforcement and studio applications.

While few electret microphones rival the best DC-polarized units in terms of noise level, this is not due to any inherent limitation of the electret. Rather, mass production techniques needed to produce electrets cheaply don't lend themselves to the precision needed to produce the highest quality microphones.

External links

  • Electret condenser Microphone structure and theory introduction
  • Guide for Electret Condenser Microphones
  • Rane schematic
  • Integrated Circuits for High Performance Electret Microphones Audio Engineering Society Convention Paper
  • Foil Electret Microphone: Sessler & West (1960)
  • Modern electret microphones and their applications
Retrieved from "http://en.wikipedia.org/wiki/Electret_microphone"