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Noise Canceling Headphones

Noise Canceling Headphones. Team Members Doan Thanh Khiet Tran Jasmine Khadem Kalina Guentcheva. Introduction.

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Noise Canceling Headphones

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  1. Noise Canceling Headphones Team Members Doan Thanh Khiet Tran Jasmine Khadem Kalina Guentcheva

  2. Introduction In today’s noisy world it is hard to find a peaceful place. This new technology of noise cancellation can block out unwanted noise (signals) around us and achieve that ‘noise free environment’. By picking up ambient sound with a microphone and reproducing it out of phase, we can actively cancel or "null" out background noise.

  3. How it works • The electronics behind this device consists of three op-amp circuits. Each circuit uses an op-amp in a different configuration. • The first circuit is a non-inverting pre-amp. • The second is a unity-gain phase-inverter. • The third is an inverting headphone amplifier.

  4. Power Plant Non-inverting pre-amp/ high pass filter Inverting amplifier Speaker Switch Microphones Inverting amplifier (unity gain) Main PCB System Overview

  5. System Overview • Power Plant used to power the system(± 9V DC). • Microphones  picks up the signal and converted into an electrical signal with a base-band bandwidth (~20 kHz). • Non-Inverting pre-amp/High-pass Filter  blocks the DC component and achieves a significant gain. • Switch directs the signal between two different paths. It can go through a unity gain inverter and/or a controllable inverting amplifier. • Inverting Amplifier (Unity gain)  amplifies the signal. • Inverting Amplifier  cancels the noise. • Speaker  the output from the inverting amplifier goes to the speaker where the user can hear either the amplified signal or have a quiet zone.

  6. Construction • There are two parts to this project: • Building the electronics • Modifying a pair of headphones

  7. Building the electronics • Non-Inverting pre-amp/High-pass Filter • The DC component and low frequency component of the audio signal (0~10 Hz) is blocked off.

  8. Bode Plot of High-Pass Filter

  9. Building the electronics • Inverting Amplifier (Unity gain) • acts as an isolation barrier between the other stages in order to minimize noise.

  10. Building the electronics • Inverting Amplifier • At this stage, the microphone signal is inverted by 180 degrees and the background noise is canceled.

  11. Overall circuit

  12. Outputs Amplifying the signal Canceling the signal

  13. Applications • Headphones that have adaptive noise cancellation are used for pilot’s radio headset in jet aircrafts. • Simply to block unwanted noise from the background.

  14. Drawbacks/Improvements • Drawback: • Consumption of power  the headphones require a battery that needs to be recharged. It also makes the headphones bulky. • Works well only if the signal is continuous  if the signal is changed frequently then the noise will not be cancelled out efficiently. • Only the hardware static filter was implemented (from 20 kHz to 30 Hz). The output is shifted by 45 degrees. • Improvement: • Using a regulator that can generate –9V from 9V battery. • Use a software control dynamic filter to achieve best performance at wide frequency range.

  15. Conclusion • We have designed and successfully implemented a noise cancellation circuit. • Fast response time is a requirement for noise cancellation system. • Power consumption optimization is particularly important for mobile scenarios.

  16. References • LM1575 Datasheet, http://cache.national.com/ds/LM/LM1575.pdf, October 26, 2006. • Head Wire: http://www.headwize.com/projects/noise_prj.html, November 2, 2006. • Active Noise Cancellation: http://www.answers.com/topic/noise-cancelling-headphone, November 21, 2006. • Adaptive Noise Cancellation:http://www.owlnet.rice.edu/~ryanking/elec431/intro.html, November 15, 2006. • Adaptive Noise Cancellation: http://www.ece.rice.edu/~klwang/elec434/elec434.htm#how, November 17, 2006.

  17. Questions ? THANK YOU

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