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Active Noise
Cancellation
Kyle Brett, Johan Kohler, Josh Tavares
ELG 4135 – Electronics III
Dr. Riadh Habash
November 28th, 2006.
Why Noise
Cancellation?
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!
How It Works (continued)
The Circuit
Simulating The Circuit
Simulation Results
Problems
1. Microphone doesn’t 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
Simulation Results
Propagation Delay
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?
Potential Solutions
1. 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
2. Phase and/or Amplitude of noise signal
must be manipulated
•
This can be achieved through filtering
Discussion of Solutions
1. 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
2. Phase and/or Amplitude of noise signal
must be manipulated
•
This can be done through filtering
3. Placement of microphone relative to
speaker
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
Discussion (continued)
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.
Results
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
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.
Simulation
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
Combining The Ideas
Discussion
• Peak value is significantly reduced, especially
for higher frequencies and larger microphone
placement distances
– More practical microphone placement positions are
achievable.
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
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
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-forchampions.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
Refrences
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•
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•
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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
THANK YOU!