Active noise control in textiles mill

BY: MRITUNJAY KUMAR M.TECH. 1ST YR.(TTE)

NOISE ?

Generally noise is an unwanted sound, regardless of its intensity or duration. noise is simply unwanted sound, so sound is not really noise unless someone hears it and finds it disturbing.

There are two different kinds of noise 1). Broadband 2). Narrowband. Broadband noise is caused by turbulences and is totally random, which means the energy is distributed equally across all frequency bands . Examples are the lowfrequency sound of a jet plane or the impulse noise of a gunshot. Narrowband noise, most energy is concentrated around specific frequencies . This kind of noise is caused by rotating machinery and is therefore periodic or nearly periodic. An example is the noise caused by a cars combustion engine.

In textile mill minimum and maximum noise level can be achive as ~ 82 dBA to 102 dBA.

Under ideal conditions: External noise is converted to electrical signal by a microphone Noise is inverted with an inverting amplifier. Inverted noise is added to the desired signal. Signal + inverted noise is sent to output. Inverted noise and external noise destructively interfere with each other All that is left is the desired signal!

To control unwanted sounds, two different approaches exist called passive and active noise control . In many cases a combination of both is used. Active noise control (ANC) is using the phenomenon of wave interference , When two waves with the same amplitude and frequency, but phase-reversed, travel in the same direction, they will neutralize each other and by virtue of destructive interference the resulting sound is null, the sound energy is transformed into heat.

A control system drives a speaker to produce a sound field that is the exact mirror-image of the offending sound (the disturbance). The speaker thus cancels the disturbance by means of destructive interference, and the net result is no sound at all.

A signal gets erased by its anti-signal. The result is zero.

Basic ANC components: an ANC system consists of the following four major parts: Plant The physical system to be controlled. A typical example is a headphone and the air inside it. Sensors The vibration sensors, microphones, or other devices that sense the primary disturbance and monitor how well the control system is performing by measuring the remaining error. Actuators The devices that physically do the work of altering the plant response,usually electromechanical devices such as speakers or vibration generators. Controller A signal processor that controls the actuators. It bases its commands on the sensor signals and on some knowledge of the plants response to the actuators.

The fundamental structure of a basic ANC system.

Different kinds of

1 . Global free space cancellation . 2 . Cavity and duct cancellation . 3 . Zone - of - silence cancellation .

ANC (The variety of behavior characteristics of sound waves in different physical surroundings allow categorization of ANC systems into three different groups)

It should be noted that active noise canceling is best suited for low frequencies First of all, for higher frequencies, the spacing requirements for free space and zone-of silence techniques become prohibitive. Second, in acoustic cavity and duct based systems, the number of modes grows rapidly with increasing frequency, which quickly makes active noise control techniques unmanageable. Third, passive treatments become more effective at higher frequencies and often provide an adequate solution without the need for active control.

ACTIVE NOISE CONTROL SYSTEMS

Two type of ANC Adaptive filtering: Feed forward system Feedback system Waveform synthesis (suited only to periodic noise) Eg- ANC use at Noise reduction in aircrafts Noise reduction in automobile industry

Feedforward system

Feedback System

Tachometer reference signal:

A OPAMP USED FOR ANC -------

2V=V0+VinV0

/V

in

= (1 jRWC)

/ (1 + jWRC)

CIRCUIT

SIMULATING THE

SIMULATION RESULTS

The principle of active sound control was first introduced by Lueg(1936) in a patent for the single channel feed-forward control of tonal disturbances propagating in a one-dimensional acoustic waveguide. [Sound and Structural Vibration, F. J. Fahy& P.Gardonio, Elsevier Publishers, 2007]

PROBLEMS1. Microphone doesnt represent noise amplitude appropriately Voltage amplitude might not be enough to cancel noise, or it might be too high.

2.

Propagation delay in the circuit causes a phase shift in the noise signal. Instead of subtracting from noise, we will be adding to it. This is partially controlled by microphone placement

POTENTIAL SOLUTIONS1.Potentiometer (variable resistor) in place of fixed resistor on the inverting amplifier

2.Phase and/or Amplitude of noise signal must be manipulatedThis can be achieved through filtering

Implements user variable gain, which allows controls over how much noise is removed

USE : Noise reduction in aircrafts Noise reduction in automobile industry

BENEFITS OF ACTIVE NOISE CONTROL The primary objective of most active noise control systems is the reduction of noise for personal comfort, reduction of stress and increased concentration. Another major benefit is low-frequency quieting for applications where passive insulation would be too expensive, inconvenient or heavy. Eg., the lead impregnated sheets used to reduce aircraft cabin propeller noise impose a severe weight penalty, but active control can perform just as well at a much smaller weight. Active noise control also reduces the vibrations induced into mechanical structures, thus prolonging lifetime and increasing efficiency. The cost for active noise canceling solutions is of course the additional power consumptionby the ANC sensors, controller and actuators, as well as increased complexity.

REFRENCES . Undersatanding active noise cancellation . By- colin H. Hansen Arnaud Duval, Jean-Franois Rondeau, Romain Bossart, Guillaume Deshayes, Francis Lhuillier, Laurent Gagliardini, Vehicle Acoustic Synthesis Method 2nd Generation: an effective hybrid simulation tool to implement acoustic lightweight strategies, SFA, Novemeber 2005 Koehler, Kenneth R., Circuits, College Physics for Students of Biology and Chemistry, 1996, http://www.rwc.uc.edu/koehler/biophys/4f.html Kreyszig, Erwin, Advanced Engineering Mathematics Eighth Edition, John Wiley & Sons, Inc, Toronto, 1999. Paulo Henrique Trombetta Zannin, and Samir N.Y. Gerges, Effects of Cup, Cushion, Headband Force, and Foam Lining on the Attenuation of an Earmuff, International Journal of Industrial Ergonomics, 2006, pp. 165-170 Weast, Robert C. ed., Handbook of Chemistry and Physics 51st Edition, Jones, The Chemical Rubber Co. Cleveland, 1970. dB Engineering - Noise, Vibration & Thermal Control Materials, 2001, http://www.800nonoise.com/foam.htm

THANK YOU!