microphone basics and types-dynamic,capacitor,carbon,crystal microphone
This page covers microphone basics and types including dynamic microphone, capacitor microphone, carbon microphone, crystal microphone, wireless microphone are covered here.
As we know our audio frequency range is from 20 Hz to 20 KHz. A good microphone is the device which respond well for this entire range of frequencies equally. Microphone converts audio signal into electrical signal which is amplified before being transmitted over cable. The same is reproduced back to audio form using loudspeaker.
There are various types of microphone based on their construction and application. It includes dynamic microphone, capacitor microphone, carbon microphone, crystal microphone, wireless microphone etc.
It is one of the good quality microphone with omnidirectional properties available at affordable cost. Dynamic microphone consists of small coil wound on a tube(referred as former), which is attached to the light disc (e.g diaphragm).
When person speaks in front of diaphragm, it makes coil and former move in and out. Due to this movement in the circular gap between the poles of permanent magnet, electromagnetic induction occurs. This results into AC voltage across the coil of same frequency as of sound. It will have impedance of the order 200 to 300 Ohms.
Capacitor microphone has two capacitor plates and hence the name. One plate is fixed while another metal foil disc acts as movable diaphragm. Due to application of sound waves, diaphragm vibrates and changes the position of metal disc. This results into change in capacitance. This with the help of battery will produce small varying voltage across the resistor R. This is given as input to the FET amplifier to produce sufficient quality electrical signal. It is used in broadcasting studios and in concerts.
It is used in telephone. In carbon microphone, carbon granules are filled in the front block attached to the diaphragm. Increase in the sound pressure squeezes granules closer and hence decreases the electrical resistance. Reduction in the pressure, increases the resistance. This results into varying current magnitude passing through the microphone.
This microphone will have high output in the order of 10 to 100 mV. The crystal microphone is omnidirectional and is cheaper. The disadvantage of crystal microphone is that it is easily damaged by moisture or heat. This type of microphone is used in cassette recorders. In this type of microphone, alternating voltage is produced when sound makes the diaphragm vibrates. The impedance is very high usually in the order of 1 to 5 MegaOhm. The charge and hence voltage is produced using piezoelectric effect in this crystal. The natural crystals used in this type of microphones are rochelle salt and quartz.