Noise Control From Concept to Application
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Periodic 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 one or two microphones and speakers to be effective. Several commercial applications have been successful: noise-cancelling headphones , active mufflers , anti- snoring devices, vocal or center channel extraction for karaoke machines , and the control of noise in air conditioning ducts.
The term "1-dimension" refers to a simple pistonic relationship between the noise and the active speaker mechanical noise reduction or between the active speaker and the listener headphones. Protection of a 3-dimension zone requires many microphones and speakers, making it more expensive. Noise reduction is more easily achieved with a single listener remaining stationary but if there are multiple listeners or if the single listener turns his head or moves throughout the space then the noise reduction challenge is made much more difficult.
High frequency waves are difficult to reduce in three dimensions due to their relatively short audio wavelength in air. In some, the most effective noise reduction in three-dimensional space involves low frequency sounds.
Commercial applications of 3-D noise reduction 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. This is because an engine's cyclic nature makes fast Fourier transform analysis and the noise cancellation easier to apply.
Proceedings of the IEEE. Dynamic noise limiter DNL is an audio noise reduction system originally introduced by Philips in for use on cassette decks. Purchasers of appliances also associate quiet with quality. The analysis of staff noise perception in their workplaces involved the application of a questionnaire, in order to characterize working conditions, comfort, and the main noise sources. It should be noted, that since in Portugal there is no legislation related to NICU design for public institutions, the checklist was based on legal requirements applicable to private healthcare units, which have specific criteria for the design, conception, and equipment that should exist in NICU. Penn State, Noise Control Engineering III: This course covers advanced methods for analyses of noise and vibration and treatments for control of noise and vibration.
Modern mobile phones use a multi-microphone design to cancel out ambient noise from the speech signal. Software is used to subtract the sound captured by the microphone s placed furthest from the mouth, from the microphone closest to the mouth, which produces a much clearer speech quality. Noise control is an active or passive means of reducing sound emissions, often for personal comfort, environmental considerations or legal compliance.
Active noise control is sound reduction using a power source. Passive noise control is sound reduction by noise-isolating materials such as insulation, sound-absorbing tiles, or a muffler rather than a power source.
Active noise canceling is best suited for low frequencies. For higher frequencies, the spacing requirements for free space and zone of silence techniques become prohibitive.
In acoustic cavity and duct based systems, the number of nodes grows rapidly with increasing frequency, which quickly makes active noise control techniques unmanageable. Passive treatments become more effective at higher frequencies and often provide an adequate solution without the need for active control.
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Patent 2,, The patent described how to cancel sinusoidal tones in ducts by phase-advancing the wave and cancelling arbitrary sounds in the region around a loudspeaker by inverting the polarity. Patent 2,, , U.
- Noise control : from concept to application / Colin Hansen - Details - Trove.
- Half a King (Shattered Sea, Book 1);
- From Concept to Application, 1st Edition.
Patent 2,, by Lawrence J. Fogel , systems were created to cancel the noise in helicopter and airplane cockpits. Its effect was limited and it was to be another twenty years before such technology reached wider adoption in automobiles. From Wikipedia, the free encyclopedia.
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May Understanding and crafting the mix: the art of recording. Focal Press. The innovative design provides exceptional noise reduction, thus reducing noise pollution — which allows work to continue on noisy projects, without disturbing the environment. All Noise Reduction Barriers are available in multiple size panels and may be combined for larger configurations.
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