moving coil microphone/ dynamic microphone | working principle |

Moving coil microphone

Basic

The moving coil microphone also called dynamic microphone. Dynamic microphone uses the principle of electromagnetic induction .when sounds pressure variation move a coil places in a magnetic field, there is a change of magnetic flux passing through the coil.

Construction


The main components of a moving coil microphone are a magnet, diaphragm and coil .these are shown in figure a .the magnet is a permanent magnet of pot type with a central pole piece ( south pole) and the peripheral pole piece ( north pole). Moving coil microphone consists of a magnet, and a diaphragm to which a coil is attached. The assembly is held in place by an outer casing and the coil can move freely over the magnet. Diaphragm is non - magnetic material and is light weight. A protective cover is used to save the delicate diaphragm and coil assembly from being mishandled. The electrical equivalent circuit for a moving coil microphone is show in figure b.

Principle of working

When sound waves strike the diaphragm it moves and hence coil moves in and out in the magnetic field. This motion changes the flux through the coil which results in emf being produced in the coil due to electromagnetic induction. The value of emf depends on the rate of change of flux and hence on the motion of the coil. The displacement of the coil depends on the pressure of sound waves on the diaphragm. Thus this microphone induces more voltage. The induced voltage is the faithful replica of the sound pressure variation.
  • Sensitivity- 30 micro-volts ( 90 dB below 1 volt).
  • Signal to noise ratio - s/N = 30 dB .
  • Distortion- less then 5%.

Merits

  • High set microphone .
  • It is microphone  reliable.
  • It does not need any external bias for its working.
  • Very low price.

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