active noise control

Video: active noise control

      Active noise control GudangMovies21 Rebahinxxi LK21

      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 developed in the late 1930s; later developmental work that began in the 1950s eventually resulted in commercial airline headsets with the technology becoming available in the late 1980s. The technology is also used in road vehicles, mobile telephones, earbuds, and headphones.


      Explanation


      Sound is a pressure wave, which consists of alternating periods of compression and rarefaction. A noise-cancellation speaker emits a sound wave with the same amplitude but with an inverted phase (also known as antiphase) relative 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 destructive interference.
      Modern active noise control is generally achieved through the use of analog circuits or digital signal processing. Adaptive algorithms are designed to analyze the waveform of the background aural or nonaural noise, then based on the specific algorithm generate a signal that will either phase shift or invert the polarity of the original signal. This inverted signal (in antiphase) is then amplified and a transducer creates a sound wave directly proportional to the amplitude of the original waveform, creating destructive interference. This effectively reduces the volume of the perceivable noise.
      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 in order to cancel the noise. 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, reducing noise in some spots while doubling noise in others. In small enclosed spaces (e.g. the passenger compartment of a car) global noise reduction can be achieved via multiple speakers and feedback microphones, and measurement of the modal responses of the enclosure.


      Applications


      Applications can be 1-dimensional or 3-dimensional, depending on the type of zone to protect. Periodic sounds, even complex ones, are easier to cancel than random sounds due to the repetition in the waveform.
      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-canceling 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-dimensional 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 their 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. The wavelength in air of sinusoidal noise at approximately 800 Hz is double the distance of the average person's left ear to the right ear; such a noise coming directly from the front will be easily reduced by an active system but coming from the side will tend to cancel at one ear while being reinforced at the other, making the noise louder, not softer. High-frequency sounds above 1000 Hz tend to cancel and reinforce unpredictably from many directions. In sum, 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 analysis and noise cancellation easier to apply.
      Modern mobile phones use a multi-microphone design to cancel out ambient noise from the speech signal. Sound is captured from the microphone(s) furthest from the mouth (the noise signal(s)) and from the one closest to the mouth (the desired signal). The signals are processed to cancel the noise from the desired signal, producing improved voice sound quality.
      In some cases, noise can be controlled by employing active vibration control. This approach is appropriate when the vibration of a structure produces unwanted noise by coupling the vibration into the surrounding air or water.


      Active vis-à-vis passive noise control


      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.


      History



      The first patent for a noise control system—U.S. patent 2,043,416—was granted to inventor Paul Lueg in 1936. The patent described 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. In the 1950s Lawrence J. Fogel patented systems to cancel the noise in helicopter and airplane cockpits. In 1957 Willard Meeker developed a working model of active noise control applied to a circumaural earmuff. This headset had an active attenuation bandwidth of approximately 50–500 Hz, with a maximum attenuation of approximately 20 dB. By the late 1980s the first commercially available active noise reduction headsets became available. They could be powered by NiCad batteries or directly from the aircraft power system.


      See also


      Active sound design
      Adaptive noise cancelling
      Coherence (physics)
      Noise-canceling microphone


      Notes




      References




      External links


      BYU physicists quiet fans in computers, office equipment
      Anti-Noise, Quieting the Environment with Active Noise Cancellation Technology, IEEE Potentials, April 1992
      Christopher E. Ruckman's ANC FAQ (This page was created in 1994 and maintained until approximately 2010, but is no longer active.)
      Waves of Silence: Digisonix, active noise control, and the digital revolution Archived 2016-03-04 at the Wayback Machine

    Kata Kunci Pencarian: active noise control

    active noise control systemactive noise controlactive noise control systems algorithms and dsp implementationsactive noise control ancactive noise control systemsactive noise control hondaactive noise control earbudsactive noise control speakeractive noise control in the new century the role and prospect of signal processingactive noise control room Search Results

    active noise control

    Daftar Isi

    Active Noise Control - Ford Expedition Forum

    Feb 24, 2018 · I feel that there is a ton less wind and road noise that in previous generations as well as my 2015 GL550 even when that had brand new tires. Even my 2007 Navigator had more wind and road noise than my 2018 Expedition. I feel that the Active Noise Control is working very well. This obviously is IMHO.

    Turn noise cancelling on and off? | Ford Expedition Forum

    Aug 11, 2019 · The way I read the order guide, "active noise control" is included on all Limited 302a and above. May 25 ...

    Active noise control - Hyundai Palisade Forum

    Nov 1, 2020 · It is mentioned here: Hyundai Motor’s World’s First Road-Noise Active Noise Control, RANC This is a page that describes RANC, which is the newer system, used on the GV80. But you'll see this quote in there: "As a result, the ANC (Active Noise Control) started to be used in the Hyundai Palisade and Kia K9."

    2018 Platinum -- Active Noise Control on/off? Fuse?

    Mar 28, 2016 · Does anybody know if there's a way to turn on/off the Enhanced Active Noise Control? (I have a 2018 Platinum Max, if it matters.) I'd like to be able to hear the difference between when the system is "working" and when it's not. The vehicle is plenty quiet, but it doesn't seem to be noticeably quieter than my old 2007 EL Limited.

    Active Noise Cancelation (ANC) issue | Ford Expedition Forum

    Mar 16, 2021 · The only symptom is a little extra noise when running the heat/AC at the 2 highest fan settings. The dealership offered to fix it, but that would have required tearing my entire dash out. The odds of them failing to replace some screws, breaking off some clips, overtightening, etc. was extremely high and the reward was low, so I opted to leave ...

    2018 Expy, what is that noise I hear in the cab?

    Aug 1, 2005 · The new expedition has "active noise control": Quote: The 2018 Expedition interior features enhanced active noise control that works like noise-cancelling headphones. It emits sound waves that cancel out unwanted sounds in the cabin such as engine, transmission and wind. That sounds like what you might be hearing!

    2023 ANC - Ford Expedition Forum

    May 23, 2023 · enhanced actv noise ctrl ford co-pilot360tmactive2.0 fordpasstm connect 4gwi-fi hotspot telematics modem ip clstr 12.4" digtl scrn siriusxm® w/360l- na ak&hi sync®4a w/evr & 15.5" scrn wireless charging pad limited functional 4-dr intell access lock/ unlock w/push-button start active noise control b&o sound system, 12 spkr class iv trlr tow ...

    BIZARRE intermittent humming/resonance in Platinum Shorty

    Aug 23, 2010 · It's definitely not coming from the engine or the engine compartment. It's inside the cabin. It sounds like it's coming from the speakers. It also sounds almost exactly like "microphone hum." But, since the stereo is off, this leads me to believe it must be the Active Noise Control. This system generates sound waves that counteract noise in the ...

    High Pitched Whine - Help Please | Ford Expedition Forum

    Jan 7, 2013 · AC and defrost work fine, auto temp control works fine... The really odd thing is that it seems to go AWAY when the A/C or defroster turns on... and none of the noise APPEARS to be at the front of the engine, it is only at the passenger firewall (for lack of a better location)...

    Rough idle after new coil packs & plugs | Ford Expedition Forum

    Feb 8, 2024 · have a 2017 v6 eco boost, replaced all 6 spark plugs & coil packs. Plugs were gapped at .032 It still has a rough idle to it, and has no get up. After hitting 3rd gear it seems to improve significantly. Trouble shooting done so far: -Pulled wires while idling to check if any deceled (change in...