A contact microphone is a form of

microphone 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 publi ...

that senses audio vibrations through contact with solid objects. Unlike normal air microphones, contact microphones are almost completely insensitive to air

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

s but transduce only structure-borne sound. Often used as acoustic leakage probes, they also enjoy wide usage by

electroacoustic music Electroacoustic music is a Music genre, genre of Western art music in which composers use recording technology and audio signal processing to manipulate the timbres of Acoustics, acoustic sounds in the creation of pieces of music. It originated a ...

artists experimenting with sound. Contact microphones can be used to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record

sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...

in challenging environments, such as underwater under high pressure.

Piezoelectric contact microphones

piezoelectric sensor A piezoelectric sensor is a device that uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The prefix ''piezo-'' is Greek for 'press' or 'squeeze ...

is the most commonly available contact microphone. It is made of a thin

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied stress (mechanics), mechanical s ...

ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...

disc glued to a thin

brass Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

or alloy metal disc (see image). The

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

produced from the sound vibrations can be measured across them. Contact microphones based on piezoelectric materials are passive and high-impedance, and they sound tinny without a matching

preamp A preamplifier, also known as a preamp, is an electronic amplifier that converts a weak electrical signal into an output signal strong enough to be noise-tolerant and strong enough for further processing, or for sending to a power amplifier a ...

. Instead of being used as a microphone, they alternatively may be used to produce sound (typically used as the

buzzer A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric (''piezo'' for short). Typical uses of buzzers and beepers include alarm devices, timers, train and confirmation of user input such ...

in computer

motherboards A motherboard, also called a mainboard, a system board, a logic board, and informally a mobo (see "Nomenclature" section), is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It holds and allow ...

) by sending voltages to them.

Coil-based contact microphones

Moving coil microphone contact microphones operate by suspending a coil of wire within a magnetic field or alternatively by suspending a magnet above a fixed coil, to

induce Induce may refer to: * Induced consumption * Induced innovation * Induced character * Induced coma * Induced menopause * Induced metric * Induced path * Induced topology * Induce (musician), American musician * Labor induction Labor indu ...

a signal directly from the object's vibrations.

References

{{Reflist Microphones

Piezoelectric contact microphones

Coil-based contact microphones

See also

References