A noise-canceling microphone is a
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 publ ...
that is designed to filter
ambient noise
Background noise or ambient noise is any sound other than the sound being monitored (primary sound). Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise levels.
Background n ...
.
Technical details
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 may refer to:
* Proximity effect (atomic physics)
* Proximity effect (audio), an increase in bass or low frequency response when a sound source is close to a microphone
* ''Proximity Effect'' (comics), a comic book series written by ...
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
Roll-off is the steepness of a transfer function with frequency, particularly in electrical network analysis, and most especially in connection with filter circuits in the transition between a passband and a stopband. It is most typically app ...
. Commercially and militarily useful noise-canceling microphones have been made since at least 1935 (
Amelia Earhart used one on her 1935 flight from Hawaii to California) and have been made since the 1940s by Roanwell,
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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
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 noise is defined as any signal other than the one being monitored.
In radio com ...
and a higher
signal-to-noise ratio.
Applications
*
Call center headsets
*
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
pilot headsets
*
Race car driver headsets
* Shipboard communications
* Video Gaming Headsets
See also
*
Noise-cancelling headphones Noise-cancelling headphones reduce unwanted ambient sounds using active noise control. This is distinct from passive headphones which, if they reduce ambient sounds at all, use techniques such as soundproofing.
Noise cancellation makes it possible ...
*
Acoustic quieting Acoustic quieting is the process of making machinery quieter by damping vibrations to prevent them from reaching the observer. Machinery vibrates, causing sound waves in air, hydroacoustic waves in water, and mechanical stresses in solid matter. ...
*
Active noise control
Active noise control (ANC), also known as noise cancellation (NC), or active noise reduction (ANR), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. The concept was first develop ...
References
U.S. Patent 7,248,708
Microphones
Noise reduction