Varieties of Different Types of Microphones

All microphones convert sound energy into electrical energy, but there are many different ways of doing the job, using electrostatics, electromagnetism, piezo electric effects or even the change in resistance of carbon granules. Microphones are used in many applications such as telephones, tape recorders, hearing aids, motion picture production, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, VoIP, and for non-acoustic purposes such as ultrasonic checking.

When it comes to microphones used in music recording or live performance the vast majority of microphones used are either capacitor or electrostatic or dynamic or electromagnetic models. Both types employ a moving diaphragm to capture the sound, but make use of a different electrical principle for converting the mechanical energy into an electrical signal. The efficiency of this conversion is very important, because the amounts of acoustic energy produced by the voices and the musical instruments are so small.

Dynamic Microphones
Dynamic microphones work via electromagnetic induction. They are robust, relatively inexpensive and resistant to moisture, and for this reason they are widely used on stage by singers. There are two basic types. The moving coil microphone and the ribbon microphone.

Dynamic microphones have the advantages of being relatively inexpensive and hard wearing, and they do not need a power supply or batteries to make them operate. A lightweight diaphragm, usually made of plastic film, is attached to a very small coil of wire suspended in the field of a permanent magnet. When a sound causes the diaphragm to vibrate, the whole assembly works as a miniature electricity generator, and a minute electric current is produced. Because the electrical output is so very small, it has to be amplified using a microphone preamp. Dynamic microphones are most effective when working with relatively loud sound sources that do not contain a lot of very high frequency details.

Capacitor Microphones
Capacitor microphones have been around for several decades, and although modern ones do incorporate a few small technical improvements, the sound character has actually changed very little. Some of the best sounding capacitor ones were designed over 20 years ago. The main part of the capacitor microphone contains a pair of conducting plates, one fixed and the other in the form of a moving diaphragm. When the spacing between the plates changes the capacitance varies, and if a fixed electrical charge is applied to the capacitor, an electrical signal is produced, which faithfully represents the diaphragm vibration.

Capacitors are more expensive than their dynamic counterparts, but they are also much more sensitive, and can capture high frequency detail much more accurately. Furthermore, the capacitor principle, unlike the dynamic principle, lends itself easily to the production of microphones with switchable pickup patterns, although the cheaper models tend to offer just a fixed Cardioid pattern.

Electret Microphones
An electret is a ferroelectric material that has been permanently electrically charged or polarized. An electret microphone is a relatively new type of capacitor microphone invented at Bell laboratories in 1962. A static charge is embedded in an electret by alignment of the static charges in the material, much the way a magnet is made by aligning the magnetic domains in a piece of iron. They are used in many applications, from high quality recording and lavalier use to built in microphones in small sound recording devices and telephones.