A microphone, colloquially called a mic or mike),is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, and radio and television broadcasting. They are also used in computers for recording voice, speech recognition, VoIP, and for other purposes such as ultrasonic sensors or knock sensors.
Several types of microphone are used today, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone, which uses a coil of wire suspended in a magnetic field; the condenser microphone, which uses the vibrating diaphragm as a capacitor plate; and the contact microphone, which uses a crystal of piezoelectric material. Microphones typically need to be connected to a preamplifier before the signal can be recorded or reproduced.
How do microphones work?The most common type of microphone, the dynamic microphone, uses a coil suspended in a magnetic field that may be attached to multiple membranes for extended frequency response.
Dynamic microphones use electrical energy in the form of induction to produce the audio signal. These microphones are well suited to stage performance.
The microphone capsule contains a small diaphragm connected to a moving coil. When sound waves hit the diaphragm, it vibrates. This causes the coil to move back and forth in the magnet's field, generating an electrical current.
However, how a microphone works ultimately varies depending on its designed purpose.
One of the main considerations, aside from the type of device, is what is being recorded. The directionality of microphones is another consideration in microphone design.
Other types of microphoneLet's now look at a few different types of microphones based on their intended purpose.
Omnidirectional microphonesOmnidirectional microphones are suited to recording all sounds in an area but are poor for focusing on a single subject among background noise.
An example of an omnidirectional microphone is the lavalier microphone, which is often used in television production.
Directional microphonesDirectional microphones, also referred to as unidirectional, are better at picking up sounds from a particular direction and are useful in situations where there is significant background noise.
Shotgun microphones are a type of directional microphone often used in film and television production to record audio from a distance.
Cardioid microphones are another type of directional microphone that is commonly used for live music recordings and performances.
Bidirectional microphonesBidirectional microphones are designed to pick up sounds from two directions, making them ideal for recording conversations.
An example of a bidirectional microphone would be those used for dictation machines.
Condenser microphonesCondenser microphones use the varied electrical charge of a capacitor with a diaphragm acting as one of the plates of a capacitor. The plate is biased by a fixed charge, often from a battery which also amplifies the signal.
The capacitance varies with the movement of the diaphragm in relation to the other plates providing the means to record the sound in the electrical signal.
For example, electret microphones are used in cellphones and computers as a type of condenser microphone that uses a polarized ferroelectric material.
Laser microphonesLaser microphones use the vibrations of surfaces affected by sound waves to capture sound at distances. The lasers return at different angles due to the vibration and these changes are interpreted and translated into sound waves.
Laser microphones are used in situations where sounds need to be recorded from a distance.
Ribbon microphonesRibbon microphones are made using a thin strip of conductive metal that is suspended in a magnetic field. The ribbon is usually made from aluminum, duralumin or nanofilm.
When sound waves hit the microphone, the ribbon vibrates, which in turn produces an electrical signal.
Ribbon microphones are often used in studios for recording music as they tend to produce a smooth, natural sound.
The most common connectors used by microphones are:
- Male XLR connector on professional microphones
- ¼ inch (sometimes referred to as 6.35 mm) phone connector on less expensive musician's microphones, using an unbalanced 1/4 inch (6.3 mm) TS (tip and sleeve) phone connector. Harmonica microphones commonly use a high impedance 1/4 inch (6.3 mm) TS connection to be run through guitar amplifiers.
- 3.5 mm (sometimes referred to as 1/8 inch mini) TRS (tip, ring and sleeve) stereo (also available as TS mono) mini phone plug on prosumer camera, recorder and computer microphones.
- USB allows direct connection to PCs. Electronics in these microphones powered over the USB connection performs preamplification and ADC before the digital audio data is transferred via the USB interface.