A noise-canceling microphone is a microphone

Microphone

A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

 designed to filter out ambient noise

Ambient noise level

In atmospheric sounding and noise pollution, ambient noise level is the background sound pressure level at a given location, normally specified as a reference level to study a new intrusive sound source.Ambient sound levels are often measured in order to map sound conditions over a...

 from the desired sound, especially useful in noisy environments.

Technical detail

The development is a special case of the differential microphone topology most commonly used to achieve directionality. All such microphones have at least two ports through which sound enters; a front port normally oriented toward the desired sound and another port that's more distant. The microphone's diaphragm is placed between the two ports; sound arriving from an ambient sound field reaches both ports more or less equally. Sound that's much closer to the front port than to the rear will make more of a pressure gradient between the front and back of the diaphragm, causing it to move more. The microphone's proximity effect

Proximity effect (audio)

The proximity effect in audio is an increase in bass or low frequency response when a sound source is close to a microphone.-Technical explanation:...

 is adjusted so that flat frequency response is achieved for sound sources very close to the front of the mic – typically 1 to 3 cm. Sounds arriving from other angles are subject to steep midrange and bass rolloff. Commercially and militarily useful noise-canceling microphones have been made since the 1940s by Roanwell, Electro-Voice and others.

Alternative technologies

Another technique uses two or more microphones and active or passive circuitry to reduce the noise. The primary microphone is closer to the desired source (like a person's mouth). A second mic receives ambient noise. In a noisy environment, both microphones receive noise at a similar level, but the primary mic receives the desired sounds more strongly. Thus if one signal is subtracted from the other (in the simplest sense, by connecting the microphones out of phase) much of the noise is canceled while the desired sound is retained. Other techniques may be used as well, such as using a directional primary mic, to maximize the difference between the two signals and make the cancellation easier to do.

The internal electronic circuitry of an active noise-canceling mic attempts to subtract noise signal from the primary microphone. The circuit may employ passive or active noise canceling techniques to filter out the noise, producing an output signal that has a lower noise floor

Noise floor

In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where the noise is defined as any signal other than the one being monitored....

 and a higher signal-to-noise ratio

Signal-to-noise ratio

Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...

.

Applications

• Call center headsets
• Helicopter
  Helicopter
  A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
  
   pilot headsets
• Race car driver headsets
• Shipboard communications
• Voxtec's Phraselator
  Phraselator
  The Phraselator is a weatherproof handheld language translation device developed by VoxTec, a former division of the military contractor Marine Acoustics, located in Annapolis, MD.-The device:...