Kyle Brett, Johan Kohler, Josh Tavares

1. Active Noise Cancellation ELG 4135 – Electronics III Dr. Riadh Habash November 28th, 2006. Kyle Brett, Johan Kohler, Josh Tavares

2. Why Noise Cancellation?

3. 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

4. How It Works (continued)

5. The Circuit

6. Simulating The Circuit

7. Simulation Results

8. Problems • Microphone doesn’t 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

9. Simulation Results Propagation Delay

10. 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?

11. 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

12. 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

13. Discussion (continued) • Variable gain will help remove more noise by increasing the noise signal amplitude • Reducing the amplitude of higher frequency noise will lighten the effects of the additive noise

14. Discussion (continued)

15. 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.

16. Results

17. 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

18. 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.

19. Simulation

20. 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

21. Combining The Ideas

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

23. 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

24. 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

25. 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 • JulesRyckebusch, “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

26. 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

27. THANK YOU!