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Microphone

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A microphone, often called a mic, is a transducer. A transducer is a device that converts one form of energy into another. In this case, it converts sound waves into electrical signals. These devices are essential for modern life. They enable telecommunication, sound recording, and broadcasting. You can find them in telephones, hearing aids, and mobile devices.

IEEE MIC
IEEE MIC

Microphones work by responding to air pressure variations. These variations are what we perceive as sound waves. There are several main types of microphones used today. The most common is the dynamic microphone. It uses a coil of wire suspended in a magnetic field. Another common type is the condenser microphone. This uses a vibrating diaphragm as a capacitor plate.

Condenser microphone
Condenser microphone

Finally, contact microphones use a crystal of piezoelectric material to create a signal.

Condenser microphones are highly detailed and popular in recording studios. They are also known as electrostatic or capacitor microphones. The core of the device is the capsule, which contains fixed and movable plates. The diaphragm acts as one of these plates. When sound waves hit the diaphragm, it vibrates. This changes the distance between the plates. In a capacitor, capacitance is inversely proportional to the distance between the plates.

Oktava319-internal
Oktava319-internal

These changes in capacitance allow the device to measure the audio signal.

There are two main ways to extract the signal from a condenser. DC-biased microphones use a fixed charge on the plates. The voltage across the capacitor changes as the capacitance changes due to vibrations. This voltage difference is then amplified. RF condenser microphones use a different method. They use a low-noise oscillator to generate a low RF voltage. The sound waves modulate either the amplitude or the frequency of this signal. This method allows for a looser diaphragm, which provides a wider frequency response.

AKG C451B
AKG C451B

Humans have sought to amplify the voice for thousands of years. In fifth-century-BC Greece, actors used theater masks with horn-shaped openings. These masks acoustically amplified voices in large amphitheaters. In the 1600s, Robert Hooke experimented with a medium other than air. He used stretched wire and cups, similar to a tin-can telephone. In 1856, Antonio Meucci developed a dynamic microphone. He used a vibrating diaphragm and an electrified magnet with a spiral wire.

David Edward Hughes
David Edward Hughes

The 1870s brought the carbon microphone, which was critical for telephony. David Hughes in England and Emile Berliner and Thomas Edison in the US developed it independently. Although Edison received the first patent in 1877, many historians credit Hughes. In 1916, E.C. Wente at Western Electric created the first condenser microphone. Later, the 1949 Neumann U 47 set a new standard for high-fidelity recording. It used a large dual-diaphragm capsule and a vacuum tube amplifier.

Western Electric double button carbon microphone
Western Electric double button carbon microphone

Modern technology relies heavily on the electret condenser microphone. Invented by Gerhard Sessler and James West at Bell Laboratories in 1962, it changed everything. An electret is a ferroelectric material with a permanent electrical charge. This charge is embedded through the alignment of static charges, much like a permanent magnet. This design is easy and inexpensive to manufacture. Because of this, over one billion electret microphones are produced every year.

They are found in almost all cell phones and computers today.

Microphones are categorized by many different characteristics. Engineers group them by their transducer principle, such as dynamic or condenser. They also categorize them by directional characteristics. These include omnidirectional, cardioid, and figure-eight patterns. Some microphones are designed to be end-address, while others are side-address. The development of these patterns allows for better control in complex environments. For example, the shotgun microphone was developed to meet the needs of booming film technology.

Shotgun microphone
Shotgun microphone
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🖼️ Images & Media (27)
File:Shure mikrofon 55S.jpg
Shure mikrofon 55S.jpg
File:David Edward Hughes.jpg
David Edward Hughes.jpg
File:Bogart Bacall AFRS.jpg
Bogart Bacall AFRS.jpg
File:Shure SM57 microphone.jpg
Shure SM57 microphone.jpg
File:Oktava319-internal.jpg
Oktava319-internal.jpg
File:Condenser microphone.svg
Condenser microphone.svg
File:AKG C451B.jpg
AKG C451B.jpg
File:US Patent 3118022 - Gerhard M. Sessler James E. West - Bell labs - electroacustic transducer - foil electret condenser microphone 1962 1964 - pages 1-3.png
US Patent 3118022 - Gerhard M. Sessler...
File:Patti Smith performing in Finland, 2007.jpg
Patti Smith performing in Finland, 2007.jpg
File:Tauchspulenmikrofon-en.svg
Tauchspulenmikrofon-en.svg
File:Edmund Lowe fsa 8b06653.jpg
Edmund Lowe fsa 8b06653.jpg
File:Western Electric double button carbon microphone.jpg
Western Electric double button carbon...

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