Katana VentraIP

Microphone

A microphone, colloquially called a mic (/mk/),[1] or mike,[a] 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 and other electronic devices, such as mobile phones, for recording sounds, speech recognition, VoIP, and other purposes, such as ultrasonic sensors or knock sensors.

For other uses, see Microphone (disambiguation).

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.

Capsule design and directivity[edit]

The inner elements of a microphone are the primary source of differences in directivity. A pressure microphone uses a diaphragm between a fixed internal volume of air and the environment and responds uniformly to pressure from all directions, so it is said to be omnidirectional. A pressure-gradient microphone uses a diaphragm that is at least partially open on both sides. The pressure difference between the two sides produces its directional characteristics. Other elements such as the external shape of the microphone and external devices such as interference tubes can also alter a microphone's directional response. A pure pressure-gradient microphone is equally sensitive to sounds arriving from front or back but insensitive to sounds arriving from the side because sound arriving at the front and back at the same time creates no gradient between the two. The characteristic directional pattern of a pure pressure-gradient microphone is like a figure-8. Other polar patterns are derived by creating a capsule that combines these two effects in different ways. The cardioid, for instance, features a partially closed backside, so its response is a combination of pressure and pressure-gradient characteristics.[44]

Microphone polar sensitivity. Microphone is parallel to the page facing upwards in each diagram.

[45]

Omnidirectional

Omnidirectional

Subcardioid

Subcardioid

Supercardioid

Supercardioid

Hypercardioid

Hypercardioid

Bi-directional or Figure-8

Bi-directional or Figure-8

Lobar

Lobar

Powering[edit]

Microphones containing active circuitry, such as most condenser microphones, require power to operate the active components. The first of these used vacuum-tube circuits with a separate power supply unit, using a multi-pin cable and connector. With the advent of solid-state amplification, the power requirements were greatly reduced and it became practical to use the same cable conductors and connector for audio and power. During the 1960s several powering methods were developed, mainly in Europe. The two dominant methods were initially defined in German DIN 45595 as de:Tonaderspeisung or T-power and DIN 45596 for phantom power. Since the 1980s, phantom power has become much more common, because the same input may be used for both powered and unpowered microphones. In consumer electronics such as DSLRs and camcorders, "plug-in power" is more common, for microphones using a 3.5 mm phone plug connector. Phantom, T-power and plug-in power are described in international standard IEC 61938.[59]

Male on professional microphones

XLR connector

14 inch (sometimes referred to as 6.35 mm) on less expensive musician's microphones, using an unbalanced 14 in (6.35 mm) TS (tip and sleeve) phone connector. Harmonica microphones commonly use a high impedance 14 inch TS connection to be run through guitar amplifiers.

phone connector

(sometimes referred to as 18 inch mini) TRS (tip, ring and sleeve) stereo (also available as TS mono) mini phone plug on prosumer camera, recorder and computer microphones.

3.5 mm

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.

USB

Systems for extracting voice input from (notably telephones, speech recognition systems, hearing aids)

ambient noise

and related technologies

Surround sound

Locating objects by sound: (e.g. military use to locate the source(s) of artillery fire). Aircraft location and tracking.

acoustic source localization

original recordings

High fidelity

3D spatial for localized acoustic detection of subcutaneous sounds

beamforming

A microphone array is any number of microphones operating in tandem. There are many applications:


Typically, an array is made up of omnidirectional microphones distributed about the perimeter of a space, linked to a computer that records and interprets the results into a coherent form.

Various microphone covers

Various microphone covers

Two recordings being made—a blimp is being used on the left. An open-cell foam windscreen is being used on the right.

Two recordings being made—a blimp is being used on the left. An open-cell foam windscreen is being used on the right.

"Dead cat" and a "dead kitten" windscreens. The dead kitten covers a stereo microphone for a DSLR camera. The difference in name is due to the size of the enclosure.

"Dead cat" and a "dead kitten" windscreens. The dead kitten covers a stereo microphone for a DSLR camera. The difference in name is due to the size of the enclosure.

Windscreens (or windshields – the terms are interchangeable) provide a method of reducing the effect of wind on microphones. While pop-screens give protection from unidirectional blasts, foam "hats" shield wind into the grille from all directions, and blimps, zeppelins, and baskets entirely enclose the microphone and protect its body as well. The latter is important because, given the extreme low-frequency content of wind noise, vibration induced in the housing of the microphone can contribute substantially to the noise output.


The shielding material used – wire gauze, fabric or foam – is designed to have a significant acoustic impedance. The relatively low particle-velocity air pressure changes that constitute sound waves can pass through with minimal attenuation, but higher particle-velocity wind is impeded to a far greater extent. Increasing the thickness of the material improves wind attenuation but also begins to compromise high-frequency audio content. This limits the practical size of simple foam screens. While foams and wire meshes can be partly or wholly self-supporting, soft fabrics and gauzes require stretching on frames or laminating with coarser structural elements.


Since all wind noise is generated at the first surface the air hits, the greater the spacing between the shield periphery and microphone capsule, the greater the noise attenuation. For an approximately spherical shield, attenuation increases by (approximately) the cube of that distance. With full basket windshields there is an additional pressure chamber effect, first explained by Joerg Wuttke,[66] which, for two-port (pressure gradient) microphones, allows the shield and microphone combination to act as a high-pass acoustic filter.


Since turbulence at a surface is the source of wind noise, reducing gross turbulence can add to noise reduction. Both aerodynamically smooth surfaces, and ones that prevent powerful vortices being generated, have been used successfully. Historically, artificial fur has proved very useful for this purpose since the fibers produce micro-turbulence and absorb energy silently. If not matted by wind and rain, the fur fibers are very transparent acoustically, but the woven or knitted backing can give significant attenuation. As a material, it suffers from being difficult to manufacture with consistency and is hard to keep in pristine condition on location. Thus there is an interest in moving away from its use.[67]

– transducer for sound within the earth

Geophone

– transducer for sound in water

Hydrophone

– plasma-based microphone

Ionophone

– computer accessory for disabling internal microphone.

Microphone blocker

Microphone connector

Nominal impedance

Corbett, Ian. Mic It!: Microphones, Microphone Techniques, and Their Impact on the Final Mix. CRC Press, 2014.

Eargle, John. The Microphone Book. Taylor & Francis, 2004.

"", historical perspective, Scientific American, July 13, 1878, p. 16

The Invention of the Microphone

Info, Pictures and Soundbytes from vintage microphones

Microphone sensitivity conversion—dB re 1 V/Pa and transfer factor mV/Pa

Searchable database of specs and component info from 1000+ microphones