Kyle Brett, Johan Kohler, Josh Tavares

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Active Noise Cancellation

• Kyle Brett, Johan Kohler, Josh Tavares

ELG 4135 Electronics III Dr. Riadh
Habash November 28th, 2006.
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Why Noise Cancellation?
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How It Works

• 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!

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How It Works (continued)
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The Circuit
6
Simulating The Circuit
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Simulation Results
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Problems

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

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Simulation Results
Propagation Delay
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Simulation Results

• Phase shift occurs due to propagation delay
• Amount of noise canceled is frequency dependent
• Propagation delay becomes more significant as the
  frequency increases.
• How can we account for this?

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Potential Solutions

• Potentiometer (variable resistor) in place of
  fixed resistor on the inverting amplifier
• Implements user variable gain, which allows
  controls over how much noise is removed
• Phase and/or Amplitude of noise signal must be
  manipulated
• This can be achieved through filtering

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Discussion of Solutions

• Potentiometer (variable resistor) in place of
  fixed resistor on the inverting amplifier
• Implements user variable gain, which allows
  controls over how much noise is removed
• Phase and/or Amplitude of noise signal must be
  manipulated
• This can be done through filtering
• Placement of microphone relative to speaker

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Discussion (continued)

1. Variable gain will help remove more noise by
   increasing the noise signal amplitude
2. Reducing the amplitude of higher frequency noise
   will lighten the effects of the additive noise

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Discussion (continued)
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Discussion (continued)

• Higher gains lead to higher peak voltages for
  noise
• Solution 1 affects solution 2.
• Filter also has a phase response,
• This could counteract the noise cancellation in a
  similar way as propagation delay.

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Results
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Results (continued)

• Filtering causes a 20 drop in the peak value.
• Peak value also shifts to a lower frequency
• Caused by phase response of the filter
• This only improves the cases where the microphone
  is more distant from the speaker

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Further Improvements

• Filter the external noise before it enters the
  ear.
• Use a foam lining on the earphone.
• Foam acts as a low pass filter
• We will model it as such.

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Simulation
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Discussion of Model

• The peak amplitude is significantly reduced
• Peak amplitude is slightly higher for higher
  frequencies
• Result is still significantly better than a
  system without the lining
• Problem This is only a model
• Out of the scope of our knowledge and we are
  forced to make an approximation

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Combining The Ideas
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Discussion

• Peak value is significantly reduced, especially
  for higher frequencies and larger microphone
  placement distances
• More practical microphone placement positions are
  achievable.

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Applications

• Reducing road noise in a vehicle.
• Help improve concentration on the road
• Increasing the enjoyment or personal music
  devices.
• By reducing the volume, damage to hearing is also
  reduced
• Could be used without a source to dampen the
  ambient noise in an environment

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Future Improvements

• Find a more optimal filter response
• Flat (or approximately flat) phase response over
  the frequencies of interested
• Find a more appropriate way to model the
  filtering action caused by the earphone

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Refrences

• Francesco Piazza, Stefano Squartini, Rolmolo
  Toppi, Massimo Navarri, M. Pontillo, Ferruccio
  Bettarelli, and Ariano Lattanzi,
  Industry-Oriented Software-Based System for
  Quality Evaluation of Vehicle Audio
  Environments, IEEE Transactions on Industrial
  Electronics, June 2006, pp. 855-866.
• S.J. Elliot and P.A. Nelson, Active Noise
  Control, IEEE Signal Processing Magazine,
  October 1993, pp. 12-35
• Jules Ryckebusch, Build These Noise-Canceling
  Headphones, Popular Electronics, September 1997
• Ron Kurtus, Active Noise Cancellation, Succeed
  in Physical Science, January 2006,
  http//www.school-for-champions.com/science/noise_
  cancellation.htm
• Sedra, Adel S. and Kenneth C. Smith,
  Microelectric Circuits Fifth Edition, Oxford
  University Press, New York, 2004
• Rose, Jay, What's the Frequency?,
  1996,http//www.dplay.com/tutorial/freqpaint.html

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Refrences

• Arnaud Duval, Jean-François 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

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THANK YOU!