MICROPHONES AND HOW IT WORKS


TYPES OF MICROPHONES

The simplest type of modern microphone is the CARBON microphone,used in telephones.This microphone consists of a metallic cup filled with carbon granules.A movable metallic diaphragm mounted in contact with the granules covers the open end of the cup. Wires attached to the cup and diaphragm are connected to an electrical circuit so that a current flows through the carbon granules. Sound waves vibrate the diaphragm,varying the pressure on the carbon granules.The electrical resistance of the carbon granules changes with the varying pressure,causing the current in the circuit to change according to the vibrations of the diaphragm. The varying current may either actuate a nearby telephone receiver or may be amplified and transmitted to a distant receiver.If the current variation is suitable amplified,it may also be used to modulate a radio transmitter.

You need a bias voltage for audio signal output from 1,5 V TO 6 V DC.

The CRYSTAL microphone,utilizes piezoelectric crystals,in which a voltage develops between two faces of the crystal when pressure is applied to the crystal.In this microphone sound waves vibrate a diaphragm,which in turn varies the pressure on a piezoelectric crystal.This generates a small voltage,which is then amplified.

Impedance: 1 Meg ohm or more.This unit could be destroyed with a bit of humidity !

RIBBON microphones:A thin metallic ribbon is attached in a magnetic field.When sound waves strike the diaphragm and vibrate the ribbon,a small voltage is generated in the ribbon by electromagnetic induction.

This unit needs a signal matching transformer like a moving coil microphone. Don't breath through this unit,because you could destroy it with your breath.


!!!! MORE INFORMATION ABOUT THE RIBBON MICROPHONE

A MOVING COIL microphone:Operates on essentially the same principle but has a coil of light wire,instead of a ribbon,attached to the diaphragm.

Impedance: 10 ohm - 200 ohm
10 K ohm - 50 K ohm for taperecorder (hi. imp.)
30 ohm - 600 ohm for mic preamp (low imp.)

CONDENSOR microphones:It has two thin metallic plates placed close to each other that serve as a capacitor.The back plate of the capacitor is fixed,and the front plate serves as the diaphragm.Sound waves alter the spacing between the plates,changing the electrical capacitance between them.Condensor microphones can be very small.A common type of condensor microphone,the electret condensor microphone,is used in hearing aids.

Needs a power supply for high D.C. voltage circuit.


MICROPHONES SCHEMATICS DESIGNED BY TOSHIO SATO,
RECORDING ENGINEER :RECORDING STUDIO "ST.TROPEZ" TOKYO JAPAN



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