Microphones

A microphone, sometimes referred to as a mike or mic (pronounced "mike"), is an acoustic to electric transducer that converts sound into an electrical signal. more...

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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 numerous other computer applications.

Invention

The word "microphone" (Greek mikros "small" and phone "sound") originally referred to a mechanical hearing aid for small sounds.

The invention of a practical microphone was crucial to the early development of the telephone system. Emile Berliner invented the first microphone on March 4, 1877, but the first useful microphone was invented by Alexander Graham Bell. Many early developments in microphone design took place in Bell Laboratories.

Principle of operation

All microphones capture sound waves with a thin, flexible diaphragm (or ribbon in the case of ribbon microphones). The vibrations of this element are then converted by various methods into an electrical signal that is an analog of the original sound. Most microphones in use today use electromagnetic generation (dynamic microphones), capacitance change (condenser microphones) or piezoelectric generation to produce the signal from mechanical vibration.

Microphone varieties

Capacitor or condenser microphones

In a capacitor microphone, also known as a condenser microphone, the diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. Since the plates are biased with a fixed charge (Q), the voltage maintained across the capacitor plates changes with the vibrations in the air, according to the capacitance equation:

where Q = charge in coulombs, C = capacitance in farads and V = potential difference in volts. The capacitance of the plates is inversely proportional to the distance between them for a parallel-plate capacitor. (See capacitance for details.):

Capacitor microphones can be expensive and require a power supply, commonly provided from mic inputs as phantom power, but give a high-quality sound signal and are now the preferred choice in laboratory and studio recording applications.

Electret capacitor microphones

An electret microphone is a relatively new type of condenser microphone invented at Bell laboratories in 1962 by Gerhard Sessler and Jim West , and often simply called an electret microphone. An electret is a dielectric material that has been permanently electrically charged or polarised. The name comes from electrostatic and magnet; a static charge is embdedded 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. Electret microphones have existed since the 1920s but were considered impractical, but they have now become the most common type of all, used in many applications from high-quality recording and lavalier use to built-in microphones in small sound recording devices and telephones. Though electret mics were once considered low-cost and low quality, the best ones can now rival capacitor mics in every respect apart from low noise and can even have the long-term stability and ultra-flat response needed for a measuring microphone. Unlike other condenser microphones they require no polarising voltage, but normally contain an integrated preamplifier which does require power (often incorrectly called polarizing power or bias). This preamp is frequently phantom powered in sound reinforcement and studio applications. While few electret microphones rival the best DC-polarized units in terms of noise level, this is not due to any inherent limitation of the electret. Rather, mass production techniques needed to produce electrets cheaply don't lend themselves to the precision needed to produce the highest quality microphones.

Read more at Wikipedia.org