Geometry.Net - Science: Active Noise Control

Chris Ruckman
Provides answers to common questions about active noise control including a discussion of popular misconceptions about what active noise control can and
http://www.erols.com/ruckman/ancfaq.htm
Active Noise Control - Wikipedia, The Free Encyclopedia
active noise control (ANC) (also known as noise cancellation, active noise reduction (ANR) or antinoise) is a method for reducing unwanted sound.
http://en.wikipedia.org/wiki/Active_noise_control

Extractions: Jump to: navigation search 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 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 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.
Active Noise Control
A site specializing in active noise control, with news, suggested reading, and links brought to you by Signal Systems Corporation.
http://www.signalsystemscorp.com/ancindex.htm

Extractions: Active Noise Control quiets offensive noise by using cancellation techniques, or anti-sound. Signal Systems Corporation's mission is to help quiet irritating noises so you can have a more peaceful life. This web site is designed to give the active noise community a common source for information about this technology, its applications and suppliers. Please use the feedback link at the bottom of each page to let us know how we can improve this site. What is active noise control? Check out the ANC FAQ Where is active noise control technology going ? Read our discussion about commercializing ANC technology
Active Noise Control FAQ V1996-03-14
This FAQ has four purposes * Provide concise, accurate answers to common questions about active noise control. * Dispel popular misconceptions about what
http://faqs.org/faqs/active-noise-control-faq/

Extractions: Help others by sharing your knowledge From: ruckman@xis.com (Dr. Chris Ruckman) Newsgroups: alt.sci.physics.acoustics comp.dsp ruckman@xis.com mail-server@rtfm.mit.edu (send usenet/news.answers/active-noise-control-faq) Like most FAQs, this is a living, evolving document. Please e-mail contributions, comments, praise, and criticisms to the FAQ maintainer (ruckman@oasys.dt.navy.mil) or post to news:alt.sci.physics.acoustics . In particular, please contribute the following: * Companies/universities that teach courses on active control * Companies that sell active control products * Interesting references from the general literature * Comments from readers who do not know much about acoustics To cite this FAQ as a reference, I suggest a citation like this: Ruckman, C.E. (1995) "Frequently Asked Questions: Active Noise Control," Internet FAQ document. Available via anonymous ftp from ftp://rtfm.mit.edu/pub/usenet/news.answers/, or via Usenet in news:news.answers. - - - - - - - - - - - - - - - - - - - - - - - Subject: 1.3. Contributors The following people contributed to the discussions upon which this FAQ is based: * rtm@sabine.acs.psu.edu
ANVC Group Homepage
ANVC The active noise and vibration control group at the School of Mechanical Engineering.
http://www.mecheng.adelaide.edu.au/anvc/home.shtml
Publications On Active Noise And Vibration Control -- Scott C. Douglas
active noise control, and its cousin, active vibration control, attempt to cancel an unwanted ``noise acoustical wave by injecting an equalbut-opposite
http://engr.smu.edu/~douglas/pubanvc.html

Extractions: Active noise control, and its cousin, active vibration control, attempt to cancel an unwanted ``noise'' acoustical wave by injecting an equal-but-opposite ``anti-noise''acoustical wave into the medium, thereby attenuating the wave via destructive interference. The origins of ANVC date back to at least 1936, when P. Leug patented the idea for sound control. It tooks nearly fifty years, however, to obtain what might be called successful ANVC, due to the level of electronic precision required to create an anti-noise signal with any great fidelity. Today, anti-noise headsets abound (I have a very cute set of Sony earbud-style `phones from Japan); these are mostly analog systems. Large-scale quieting requires the use of adaptive digital signal processing technology in all but the simplest acoustic environments. I began my study of ANVC as a summer hire at SRI International, Menlo Park, CA, in 1992. While working in the Acoustics and Radar Technology Laboratory, I helped develop the algorithms and guide software code developers to implement a simple one-input, one-output, one-error active noise control system that illustrated some of the advantages that simple adaptive processing has over more-costly off-line calibration methods. I also developed the multichannel extensions of the algorithms and wrote an internal SRI report that helped others to design a real-time multichannel active noise control system for reverberant room noise control. After joining the University of Utah, I remained as a consultant to SRI, developing normalized LMS algorithms for multichannel active noise control and studying simplified
Active Noise Control FAQ
The FAQ you are now reading discusses active noise control, a way of using basic physics to control noise and/or vibration. What is an FAQ, you say?
http://www.chrisruckman.com/ancfaq.htm

Extractions: What is an FAQ, you say? It's a "Frequently Asked Questions list." The Internet supports thousands of "newsgroups" - discussion forums covering every imaginable topic. When certain questions tend to get asked over and over again, it's common to assemble the answers into a list for easy reference.
Active Noise Control : Internet Resources
www.hh.se/staff/wolfgang/orpheus/anclinks.html Similar pages The U of U active noise control Web PageThis web page is a compendium of information about on-going research in active noise control at the University of Utah. Included are course descriptions,
http://www.hh.se/staff/wolfgang/orpheus/anclinks.html
Active Noise Cancellation - Succeed In Physical Science: School For Champions
DARPA DSO Defense Sciences Office sponsors research and development in the application of smart materials to active noise control problems.
http://www.school-for-champions.com/science/noise_cancellation.htm

Extractions: The School for Champions is an educational website that shows you how to achieve your dreams. Search site SfC Home Physical Science Active Noise Cancellation - Succeed in Physical Science. Also refer to physics, acoustics, sine waves, compression, phase, ear, earphones, microphone, detector, interference, waveform, Ron Kurtus, School for Champions. by Ron Kurtus (revised 21 February 2007) Noise cancellation is a method to reduce or completely cancel out undesirable sound, such that you can't hear it. It is often call Active Noise Cancellation Questions you may have about such a device are: This lesson will answer these questions. There is a mini-quiz near the end of the lesson. Useful tools: Metric-English Conversion Scientific Calculator Although sound is a compression wave, each tone or frequency can be represented by a sine wave of a given wavelength. Simple sine wave for single sound frequency Suppose another pure sound of the same frequency was emitted, but just a fraction of a second later. That means it is slightly out of phase from the first sound or sine wave. The visual representation of the two waves would be as in the next illustration.
Active Noise Control - IEEE Signal Processing Magazine
Your browser may not have a PDF reader available. Google recommends visiting our text version of this document.
http://ieeexplore.ieee.org/iel4/79/6366/00248551.pdf
ISVR - Institute Of Sound And Vibration Research
active noise control systems have been developed to overcome the active noise control tries to eliminate sound components by adding the exact opposite
http://www.isvr.soton.ac.uk/SPCG/Tutorial/Tutorial/Tutorial_files/Web-further-an

Extractions: UNIVERSITY OF SOUTHAMPTON FURTHER CONCEPTS Active Noise Control in a Room ACTIVE NOISE CONTROL The ISVR has been involved in active control research for many years. Early work was carried out on active headsets, and further studies were undertaken on the active control of enclosed soundfields. Why Active Noise Control ? There are several ways to reduce the noise levels emitted by a sound source in a room. One standard approach consists of passive noise absorption , i.e. covering the walls with absorbing materials like glassfibre coatings. These materials dissipate acoustic energy into heat and so contribute to the noise reduction, but they work best at high frequencies (e.g. above 500 Hz). Active Noise Control systems have been developed to overcome the limitations of passive strategies at low-frequencies (e.g. below 100 Hz). How does it work ?
Science Search > Active Noise Control
Research results and software tools for using smart materials in active noise control. active noise control and noise cancellation solutions for ac
http://www.science-search.org/index/Technology/Acoustics,044_Ultrasound_and_Vibr
Figure 7
Figure 7 active noise control. Adaptive signal processing is also the key technology behind active noise control whereby antiphase noise is introduced to
http://www.eee.strath.ac.uk/r.w.stewart/adaptivejava/docs/active.htm

Extractions: Figure 7: Active Noise Control. Adaptive signal processing is also the key technology behind active noise control whereby anti-phase noise is introduced to destructively interfere with environment noise. In this application the error signal is actually formed by the error microphone and this is fedback to update the LMS adaptive controller.
Wiley::Active Noise Control Systems: Algorithms And DSP Implementations
active noise control (ANC) is rapidly becoming the most effective way to reduce noises that can otherwise be very difficult and expensive to control.
http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471134244.html

Extractions: United States Change Location Join an Engineering Mailing List . Exclusive offers, news and more. Related Titles More By These Authors Embedded Signal Processing with the Micro Signal Architecture Real-Time Digital Signal Processing: Implementations and Applications, 2nd Edition Signal Processing A Course in Digital Signal Processing by Boaz Porat A Simple Approach to Digital Signal Processing by Craig Marven, Gillian Ewers The STÆDT Program by John D. Baker, Floyd M. Gardner DSP Applications Using C and the TMS320C6x DSK by Rulph Chassaing Biomedical Signal Analysis: A Case-Study Approach by Rangaraj M. Rangayyan Click to Close
Experiment
With this shareware, you can test and experiment with a very simple active noise control system at home. The purpose of this experiment is to demonstrate
http://www.val.me.vt.edu/Experiment/experiments.html

Extractions: With this shareware, you can test and experiment with a very simple active noise control system at home. The purpose of this experiment is to demonstrate active noise control. The basic principle of active noise control is to cancel a sound wave (noise) by emitting a secondary opposite (out-of-phase) sound wave (control wave). The active noise control principle is illustrated in the figure below. In the real world, the implementation of active noise control is much more complex due to phase and spatial matching, efficient transducers, system identification, etc., as explained in the paper " Active Control of Sound and Vibration ," by C. R. Fuller and A. H. Flotow. The shareware that you can download, sends a single frequency wave (sine wave at 1000 Hz) to your right speaker. This sound wave represents the noise to be cancelled. By activating the control (pushing on the control button in the program), sound wave of equal amplitude and opposite phase is sent to the left speaker to cancel the noise. Note that for an effective demonstration, the two speakers should face each other and be close to one another (see picture above). If desired, the speakers can then be moved apart and the resulting effect on the sound cancellation observed. This share was tested using "Labtec LCS-800" speakers; the sound cancellation obtained was large and appreciable. Note that the control results depends highly on the quality of speakers used. Please make sure that the volume of each speaker is set to be identical. Also notice that this experiment is more impressive at medium-high volume (please be careful not to overdrive your speakers and ears!).
ScienceDirect - Journal Of Sound And Vibration : ACTIVE NOISE CONTROL ALGORITHM
Your browser may not have a PDF reader available. Google recommends visiting our text version of this document.
http://linkinghub.elsevier.com/retrieve/pii/S0022460X9993047X
Active Noise Control Products Information On GlobalSpec
Active noise and vibration control systems are products such as controllers, sensors and actuators that monitor and cancel noise and/or vibration.
http://sensors-transducers.globalspec.com/LearnMore/Sensors_Transducers_Detector

Extractions: Show all Active Noise Control Products companies Active noise control products use electro-acoustical sound field modification or cancellation to attenuate or eliminate unwanted sound. By contrast, passive noise control products use materials to absorb sound. Active noise control products include controllers, sensors, actuators, and other electro-acoustical products for limiting or canceling noise or vibration. In a typical active noise control system, sensors are used to detect unwanted sound when it occurs. A controller and speaker are then used to create a sound field that is a twin of the unwanted sound, but inverted, so that it is a mirror image of the sound to be eliminated an anti-sound.
Cookies Required
Electronic delay has been a critical problem in active noise control (ANC) systems. This is true whether a feedforward structure or a feedback structure is
http://link.aip.org/link/?JASMAN/111/916/1
Active Noise Control Equipment On ThomasNet.com
Company Profile Manufacturer distributor of active noise control equipment. Noise control, vibration control, acoustical, soundproofing fire retardant
http://www.thomasnet.com/products/noise-control-equipment-active-53824801-1.html

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ASA 147th Meeting Lay Language Papers -Active Noise Control
active noise control, the suppression of an undesired sound by the action of another sound, has had a long and not entirely painless development arc over
http://www.acoustics.org/press/147th/active-noise.htm

Extractions: May 2004 Active noise control, the suppression of an undesired sound by the action of another sound, has had a long and not entirely painless development arc over the past 70 years. From its genesis in the 1930s, to the current state with consumer products on the market, the development of active noise control has closely paralleled and depended upon the advancement of low-cost electronics. The basic elements of an active noise control system include one or more microphones to sense the noise over some location of interest and a means to produce an appropriately tailored sound field that acts as a "control field." The control field is usually created through the action of a control system connected to loudspeakers. Applications of the concept have included control of noise produced by industrial fans, suppression of noise in heating, ventilation, and air conditioning ducts, reduction of vehicle exhaust sounds, creation of "quiet zones" within vehicle interiors, reduction of the noise levels inside aircraft and spacecraft launch fairings, and the now almost commonplace active noise control headsets in aviation and consumer use.

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