Microphone Basics and Types Explained

This article covers the basics of microphones and different types, including dynamic, capacitor, carbon, crystal, and wireless microphones.

Our audio frequency range spans from 20 Hz to 20 kHz. A high-quality microphone ideally responds well across this entire range of frequencies with equal sensitivity. A microphone converts audio signals into electrical signals, which are then amplified before being transmitted via cable. These electrical signals are subsequently converted back into audio using a loudspeaker.

Various microphone types exist, categorized by their construction and application. These include dynamic, capacitor, carbon, crystal, and wireless microphones.

Dynamic Microphone

Dynamic Microphone

Dynamic microphones are known for their good quality and omnidirectional properties, all at an affordable price. They consist of a small coil wound on a tube (the former), which is attached to a light disc (the diaphragm). When someone speaks into the microphone, the diaphragm moves, causing the coil and former to move in and out.

This movement occurs within a circular gap between the poles of a permanent magnet, leading to electromagnetic induction. This induction results in an AC voltage across the coil, with the same frequency as the sound. The impedance is typically in the range of 200 to 300 Ohms.

Capacitor Microphone

Capacitor microphones get their name from their use of two capacitor plates. One plate is fixed, while the other, a metal foil disc, serves as a movable diaphragm.

Sound waves cause the diaphragm to vibrate, changing the position of the metal disc. This change in position leads to a change in capacitance. With the help of a battery, this changing capacitance produces a small, varying voltage across a resistor, denoted as R. This voltage is then fed into a FET amplifier to produce a sufficiently high-quality electrical signal.

Capacitor microphones are commonly used in broadcasting studios and at concerts.

Carbon Microphone

Carbon microphones are commonly found in telephones. Inside a carbon microphone, carbon granules are packed into the front block, which is connected to the diaphragm.

Increased sound pressure squeezes the granules closer together, reducing electrical resistance. Conversely, reduced pressure increases the resistance. This varying resistance results in a varying current magnitude passing through the microphone.

Crystal Microphone

Crystal microphones offer a high output, typically in the range of 10 to 100 mV.

These microphones are omnidirectional and relatively inexpensive. However, a significant disadvantage is their susceptibility to damage from moisture or heat.

Crystal microphones are often used in cassette recorders. In this type of microphone, alternating voltage is produced when sound vibrates the diaphragm. The impedance is very high, usually in the order of 1 to 5 MegaOhms.

The charge, and hence voltage, is generated using the piezoelectric effect within a crystal. Common crystals used in these microphones include Rochelle salt and quartz.

Wireless Microphone

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