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Topic: Active noise control

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	Active Noise Control
		In the case of noise control, the output of the adaptive filter drives the secondary loudspeaker, and the error signal is derived by the microphone only at the end of the secondary path.
		Active noise control is a possibility for efficient noise suppression, even if the spectra of the speech and the noise are overlapped in the frequency domain.
		The noise generated by the combustion chamber of the furnace has different injurious influences: in extreme situations it can destroy the equipment, but even at normal conditions the noise is harmful for the personnel working in the boiler room.
	home.mit.bme.hu /~sujbert/active.html (1409 words)

	Active noise control - Wikipedia, the free encyclopedia
		Active noise control (also known as noise cancellation, active noise reduction (ANR) or antinoise) is a method for reducing unwanted sound.
		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 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.
	en.wikipedia.org /wiki/Active_noise_control (502 words)

	Active Noise Control FAQ v1996-01-11 (Site not responding. Last check: 2007-10-11)
		In control systems parlance, the four major parts of an active control system are: * The plant is the physical system to be controlled; typical examples are a headphone and the air inside it, or air traveling through an air-conditioning duct.
		Active control became a "mainstream" research topic in the 1970s and 1980s, and in recent years research papers have been published at the rate of several hundred per year.
		Reduction of helicopter cabin noise by active vibration isolation of the rotor and gearbox from the cabin.
	web.bilkent.edu.tr /Online/FAQ/tmp/active-noise-control-faq/faq.html (5970 words)

	ANC Status (Site not responding. Last check: 2007-10-11)
		Many people have heard of active noise control, but with the exception of headphones, few people have experienced its benefits.
		The result is that other applications of active noise control have been in industrial situations, where the benefit for active noise control is driven by hearing safety concerns.
		The result is that the pervasive use of active noise control still waits for the "killer-app" that can propel it out of the one-of-a-kind, custom project cycle that best describes how much of active noise control technology is applied today.
	www.signalsystemscorp.com /anc_status.htm (614 words)

	Active Noise control of ducted fan - Sutliff (Site not responding. Last check: 2007-10-11)
		The data show that digital RPM feedforward active noise control {ANC} applied to a ducted propeller is both feasible and serves as a good method for evaluation of the relative importance of those parameters relevant to active noise control.
		By reducing the noise in the duct, the benefits are realized throughout the environment: lowered flyby noise over neighborhoods, reduced acoustic fatigue on aircraft fuselage, and improved passenger comfort may be derived from one system.
		Transformation ANC methods employing an acoustic error sensor have stability and convergence criteria that may not be useful when applied to real sources (i.e., on the order of several minutes or more).
	www.skyaid.org /Skycar/active_noise_control_ducted_fan.htm (517 words)

	Non-linear reduced-phase filters for active noise control - Patent 5828760 (Site not responding. Last check: 2007-10-11)
		Any residual noise which is not canceled by the anti-noise from the speaker 24 is sensed by the error microphone 16 and provided to the controller 20 on the line 18 as the electrical error signal (e).
		The controller 20 adjusts the output signal (U) on the line 22 to the speaker 24 so as to reduce the total acoustic noise at the microphone 16 (and the error signal (e)), and, thus, reduce (or attenuate) the propagating noise in the duct (in a certain frequency range) downstream of the speaker 24.
		In an ideal collocated active duct noise control system, the transfer function from the input disturbance d to the anti-noise signal y seen at the microphone 16 (the closed loop transfer function y/d) is equal to -1, i.e., a magnitude of 1 and a phase of 180.degree..
	www.freepatentsonline.com /5828760.html (3643 words)

	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 the past 70 years.
		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.
		Active noise control was invented by Paul Lueg in Germany in 1932.
	www.acoustics.org /press/147th/active-noise.htm (805 words)

	Noise Control - Soundproofing Manufacturers > Sound Barriers, Soundproofing Materials Manufacturers (Site not responding. Last check: 2007-10-11)
		Noise control products can be anything from earplugs to wall panels, as long as they meet regulatory standards for reducing noise and creating a safer, quieter environment.
		One approach to eliminating or controlling noise is containing noise at its source by using mufflers, engineering controls, etc. Another is identifying, isolating and treating with barriers, absorbers and dampers the many paths along which noise travels.
		They reduce noise by allowing the sound energy to penetrate into the material and be dissipated by its cellular or fibrous nature prior to reaching the reflective surface.
	www.iqsdirectory.com /soundproofing (1983 words)

	Institute of Noise Control Engineering USA
		The introduction is a summary of the history of active control, and a review of areas in which active control has been applied in the past and will be applied in the future.
		Noise cancellation itself is a minor part of the book - appearing only in one chapter on learning strategies, but many of the techniques in the book should be applicable to the design of active noise control systems.
		Noise is clearly a factor in pump design, but this topic is mentioned only briefly in Chapter 17 which is titled "Effect of Pump Speed on Selection, Design, and Use." The author points out several benefits that will (and will not) occur when pump speed is reduced.
	www.inceusa.org /pubs.booklist.asp (4902 words)

	First Test of Fan Active Noise Control (ANC) Completed (Site not responding. Last check: 2007-10-11)
		The first active noise control test on the low-speed fan test bed was a General Electric Company system designed to control either the exhaust or inlet fan tone.
		The computer then controls the "ring source" to generate waves that have the same spinning structure and amplitude, but 180° out of phase with the fan noise.
		In addition, the far-field noise was measured with a semicircular array of 28 microphones.
	www.lerc.nasa.gov /WWW/RT1995/2000/2770h.htm (381 words)

	Campanella Associates (Acoustics Consultants) - Active Noise Control
		ANC uses the principle of destructive interference, where the noise sound wave is sensed with a microphone.
		Noise cancellation is truly outstanding at low frequencies down to 20 Hz or less (inside the ear cup only - at your ear), depending on the quality of ear cup seal around your ear.
		Inquiries on the feasibility of ANC for noise (by the highway and at house windows) have been received recently.
	www.campanellaacoustics.com /anc.htm (723 words)

	Active Noise Control in Home Environment
		Disturbing noise is nowadays a major problem in the society as a whole.
		The problem is to generate a signal that destructively interfere with the disturbing noise in the vicinity of the ear but don’t affect useful signals.
		In this project a control DSP is used that adaptively manipulates a measured noise reference and feeds the resulting signal to a pair of open headphones.
	www.e.kth.se /~e98_pry (217 words)

	Active Noise & Vibration Control Group
		The Active Noise & Vibration Control Group was established in 1987 with a grant from the Sir Ross and Sir Keith Smith fund for fundamental studies leading to a system to actively control aircraft cabin noise.
		The aim of the group is to undertake fundamental and applied research in active noise and vibration control and to apply the results of research to the development of commercial controllers and to the installation of practical systems in industry.
		Qiu, X. and Hansen, C.H. An adaptive sound intensity control algorithm for active control of transformer noise", Proceedings of the 5th International Congress of Sound and Vibration, 205-212.
	www.mecheng.adelaide.edu.au /anvc/backup (1025 words)

	Design of Active Noise Control for Speech Signal (Site not responding. Last check: 2007-10-11)
		It is well known that to cancel the noise component present in the received signal using adaptive signal processing technique, we need to have a reference signal, which is highly correlated to the noise.
		This generated signal is used to generate correlated noise, using adaptive signal processing techniques, which, again using adaptive signal processing techniques is finally used to the reduce the noise content of the received signal.[2] A technique to generate a signal correlated to the actual signal, which is the crux of this paper, is presented next.
		This estimated signal is used to extract noise from the received signal using the interference cancellation technique of the adaptive signal processing, thus giving us noise which, to a good extent, will be correlated to the noise, present in the received signal.
	www.acadjournal.com /2005/v16/part1/p3 (2494 words)

	Acoust., Vib. & Sig. Proc.: ANC (Site not responding. Last check: 2007-10-11)
		All of the parameters required to optimise an active noise control system can be adjusted through an onboard menu system, which can be accessed from a PC through a serial port connection.
		Typical systems feature a controller, actuators and sensors which work together to eliminate unwanted vibration and noise or to produce precise forces or motions, depending on the application.
		This energy management-based control technology is aimed at smart structures, one of the fastest growing market segments in vibration and noise control systems.
	www.ecgcorp.com /avsite/avdocs/active.html (456 words)

	news.answers/active-noise-control-faq
		The plant is the physical system to be controlled; typical examples are a headphone and the air inside it, or air traveling through an air-conditioning duct.
		The controller is a signal processor (usually digital) that tells the actuators what to do; the controller bases its commands on sensor signals and, usually, on some knowledge of how the plant responds to the actuators.
		Active vibration control is a related technique that resembles active noise control.
	www.ufaqs.com /usenet/active-noise-control-faq.htm (6146 words)

	Active vibration control - Wikipedia, the free encyclopedia
		Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external vibration.
		Active Vibration Control is now also commercially available for reducing vibration in helicopters, offering better comfort with less weight than traditional passive technologies.
		If the vibration is periodic, the control system may adapt to the ongoing vibration, thereby providing better cancellation than would have been provided simply by reacting to each new acceleration without referring to past accelerations.
	en.wikipedia.org /wiki/Active_vibration_control (284 words)

	Acousti Products - Active Noise Control 'Anti-Noise' in Silencing Hardware Noise
		This noise can cause significant problems, for example, a stack of several blade servers can produce noise in excess of 85dB(A) which can be extremely difficult and stressful to work next to, and will require action by law once the European Directive is implemented in April 2006.
		A standard Active Noise Cancellation System uses a sensor/microphone near the sound source, a processor to compute the exact mirror of the original sound, a speaker to emit the sound and error microphones to detect when the system is not working and to correct it via the processor.
		Active Noise Control can be particularly effective for low-frequency sound waves.
	www.acoustiproducts.com /en/cebit2006.asp (592 words)

	Amazon.com: Active Noise Control Primer: Books: Scott D. Snyder (Site not responding. Last check: 2007-10-11)
		Active noise control - the reduction of noise by generating an acoustic signal that actively interferes with the noise - has become an active area of basic research and engineering applications.
		The aim of this book is to present all of the basic knowledge one needs for assessing how useful active noise control will be for a given problem and then to provide some guidance for designing, setting up, and tuning an active noise-control system.
		Written for students who have no prior knowledge of acoustics, signal processing, or noise control but who do have a reasonable grasp of basic physics and mathematics, the book is short and descriptive.
	www.amazon.com /Active-Noise-Control-Primer-Snyder/dp/038798951X (907 words)

	Active Noise and Vibration Control
		In the last decade, active control of sound and vibration (at audio frequencies) has emerged as a viable technology to bridge the low-frequency technology gap.
		We are investigating Active Structural Acoustic Control (ASAC) on the enclosure, and Active Noise Control (ANC) in the enclosed space.
		For ANC we propose to look at the three-dimensional problem with special emphasis on hitherto neglected aspects of feedback control.
	control.ee.ethz.ch /~anc (283 words)

	Active Noise Control (Site not responding. Last check: 2007-10-11)
		Noise protection of sensitive equipment in aerospace structures has become more and more important during the last years.
		Noise attenuation can be achieved either by passive or active damping methods.
		Active methods for noise reduction (ANR) have been investigated during the last years.
	www.isd.uni-stuttgart.de /~deuble/structural_acoustics.html (381 words)

	Active Noise Control FAQ v1996-03-14 FAQ (Site not responding. Last check: 2007-10-11)
		SUMMARY: The FAQ you are now reading discusses active noise control, a novel way of using basic physics to control noise and/or vibration.
		For example, many active mufflers include a low-back- pressure "glass-pack" muffler for mid and high frequencies, with active control used only for the lowest frequencies.
		Easier still is controlling low-frequency noise in a duct, where two dimensions of the enclosed space are small with respect to wavelength.
	www.non.com /news.answers/active-noise-control-faq.html (5564 words)

	4aSA10 An active noise control stethoscope. (Site not responding. Last check: 2007-10-11)
		Using a conventional stethoscope to detect lung noises and blood pressure is difficult in many emergency medical environments, such as helicopters.
		Acoustical noise and vibrations that are detected by the stethoscope are digitally subtracted out of the stethoscope signal.
		Unwanted noise penetrating the shell of the earcup is eliminated by broadcasting counteracting ``antinoise'' in addition to the amplified stethoscope signal.
	www.auditory.org /asamtgs/asa92nwo/4aSA/4aSA10.html (127 words)

	Active Noise Control (Site not responding. Last check: 2007-10-11)
		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.
	www.signalsystemscorp.com /ancindex.htm (82 words)

	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 equal-but-opposite ``anti-noise''acoustical wave into the medium, thereby attenuating the wave via destructive interference.
		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 partial-update schemes for the task.
		While at the University of Utah, Marc Bodson and I jointly oversaw the design and construction of a six-input, six-output active noise control system that continues to be a testbed for algorithm development.
	engr.smu.edu /~douglas/pubanvc.html (1263 words)

	Active Noise Control FAQ
		The FAQ you are now reading discusses active noise control, a novel way of using basic physics to control noise and/or vibration.
		Provide concise, accurate answers to common questions about active noise control.
		Dispel popular misconceptions about what active noise control can and cannot do.
	stason.org /TULARC/physics/noise-control-faq/index.html (176 words)

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