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Active noise control (ANC) (also known as noise cancellation, active noise reduction (ANR) or antinoise) is a method for reducing unwanted sound. Sound is a disturbance of mechanical energy that propagates through matter as a wave. ...
Explanation
Sound is a pressure wave, which consists of a compression phase and a rarefaction phase. A noise-cancellation speaker emits a sound wave with the same amplitude and the opposite polarity (in antiphase) to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out - an effect which is called phase cancellation. Depending on the circumstances and the method used, the resulting soundwave may be so faint as to be inaudible to human ears. A pressure wave in a fluid is a travelling disturbance consisting in a local change of pressure (hence the name). ...
Bold text Wiktionary has related dictionary definitions, such as: compressor, compression inthe wkjhrlfidhb;g/df == Compressor may refer to: Gas compressor, a mechanical device that compresses a gas e. ...
Rarefaction is the reduction of a mediums density, or the opposite of compression. ...
Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ...
The polarity of an object is, in general, its physical alignment of atoms. ...
Phase difference is expressed in degrees from 0° to 360°, or in radians. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
Phase cancellation refers to the effect of two waves that are out of phase with each other being summed. ...
A noise-cancellation speaker may be co-located with the sound source to be attenuated. In this case it must have the same audio power level as the source of the unwanted sound. Alternatively, the transducer emitting the cancellation signal may be located at the location where sound attenuation is wanted (e.g. the user's ear). This requires a much lower power level for cancellation but is effective only for a single user. Noise cancellation at other locations is more difficult as the three dimensional wavefronts of the unwanted sound and the cancellation signal could match and create alternating zones of constructive and destructive interference. In small enclosed spaces (eg the passenger compartment of a car) such global cancellation can be achieved via multiple speakers and feedback microphones, and measurement of the modal responses of the enclosure.
Modern active noise control is achieved through the use of a computer, which analyzes the waveform of the background aural or nonaural noise, then generates a polarisation reversed waveform to cancel it out by interference. This waveform has identical or directly proportional amplitude to the waveform of the original noise, but its polarity is reversed. This creates the destructive interference that reduces the amplitude of the perceived noise. Environmental Noise is unwanted sound, which may cause both nuisance and damage to health. ...
In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. ...
This article treats polarization in electrodynamics. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
In mathematics, two quantities are called proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio. ...
The polarity of an object is, in general, its physical alignment of atoms. ...
This method differs from passive noise control methods (soundproofing) in that a powered system is involved, rather than unpowered methods such as insulation, sound-absorbing ceiling tiles or muffler. Soundproofing is any means of to reducing the intensity of sound with respect to a specified source and receptor. ...
Muffler and exhaust pipe on a Ducati 695 A muffler (or silencer in British English) is a device for reducing the amount of noise emitted by a machine. ...
The advantages of active noise control methods compared to passive ones are that they are generally:
- More effective at low frequencies.
- Less bulky.
- Able to block noise selectively.
The first patent for a noise control system was granted to inventor Paul Lueg in 1934 U.S. Patent 2,043,416 , describing how to cancel sinusoidal tones in ducts by phase-advancing the wave and canceling arbitrary sounds in the region around a loudspeaker by inverting the polarity. By the 1950s, systems were created to cancel the noise in airplane cockpits. In 1986, Dick Rutan and Jeana Yeager used prototype headsets built by Bose in their around-the-world flight.[1][2] Richard “Dick†Rutan (born July 1, 1938) is an aviator who is most famous for flying the Voyager aircraft around the world non-stop with the assistance of Jeana Yeager. ...
Jeana Yeager (born May 18, 1952 in Fort Worth, Texas) is an aviator, most famous for flying with Dick Rutan on a non-stop, non-refueled flight around the world in the Voyager aircraft in 1986 from December 14 to December 23. ...
The Bose Corporation is a privately held American company based in Framingham, Massachusetts that specializes in audio equipment. ...
Applications Applications can be 1-dimensional or 3-dimensional, depending on the type of zone to protect. Cyclic sounds, even complex ones, are easier to cancel than random sounds due to the repetition in the wave form.
Protection of a 1-dimension zone is easier and requires only a couple of microphones and speakers to be effective. Several commercial applications have been successful: noise-cancelling headphones, active mufflers, and the control of noise in air conditioning ducts. Noise-cancelling headphones reduce unwanted ambient sounds (i. ...
Protection of a 3-dimension zone requires many microphones and speakers, making it less cost-effective. Commercial applications include the protection of aircraft cabins and car interiors, but in these situations, protection is mainly limited to the cancellation of repetitive (or periodic) noise such as engine-, propeller- or rotor-induced noise.
Antinoise is used to reduce noise at the working environment with ear plugs. Bigger noise cancellation systems are used for ship engines or tunnels. An engines' cyclic nature makes FFT analysis and the noise canceling easier to apply. An earplug is a piece of protective clothing that is meant to be inserted in the ear canal to protect the wearers hearing from loud noises or the intrusion of water. ...
A disused railway tunnel now converted to pedestrian and bicycle use, near Houyet, Belgium A tunnel is an underground passage. ...
The application of active noise reduction produced by engines has various benefits: An engine in the broadest sense, is something that produces an output effect from a given input. ...
- The operation of the engines is more convenient for personnel.
- Noise reduction eliminates vibrations that cause material wearout and increased fuel consumption.
- Quieting of submarines.
Look up vibration in Wiktionary, the free dictionary. ...
Fuel imports in 2005 Fuel is any material that is capable of releasing energy when its chemical or physical structure is altered. ...
See also Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external vibration. ...
Noise-cancelling headphones reduce unwanted ambient sounds (i. ...
Coherence is the property of wave-like states that enables them to exhibit interference. ...
External links Image File history File links Wikibooks-logo-en. ...
The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization incorporated in the State of New York, United States. ...
Year 1992 (MCMXCII) was a leap year starting on Wednesday (link will display full 1992 Gregorian calendar). ...
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