Noise Canceling Headphones

Team MembersDoan Thanh Khiet Tran

Jasmine KhademKalina Guentcheva

IntroductionIn 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.

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.

System Overview

PowerPlant

Non-inverting pre-amp/ high pass filter

Inverting amplifier (unity gain)

Inverting amplifier

Speaker

Main PCB

Switch

Microphones

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.

Construction There are two parts to this project:

Building the electronics

Modifying a pair of headphones

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.

R21k VEE

-12V

R1

33k

C4

0.01uF

Microphone_Input_Signal2mV 20kHz 0Deg

R41.1M

C510uF

3

0

2

0

1

VEE

VSS

12VVSS

0

4

Out put of St age 1( Pr e- amp and hi gh pass fi l t erResponse ~ 30Hz- 20KHz @30dB)

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Bode Plot of High-Pass Filter

Building the electronics Inverting Amplifier (Unity gain)

acts as an isolation barrier between the other stages in order to minimize noise.

R3

10k

R5

10k

VEE-12V

VSS

12V

S1

Key = B

6

VSS

VEE1

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Out put of St age 1( Pr e- amp and hi gh pass fi l t erResponse ~ 30Hz- 20KHz @30dB)

4

0

2

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To I nver t i ng Ampl i fi er( St age 3)

Building the electronics

R8

100k

R6

56

R94.75k

J1

HDR1X2Speaker Connector

R7

1k

VSS

12V

VEE

-12V

R10

100K_LINKey = Space

50%

4

0

2

VEE

VSS

1

0

OffPage2

Fr om Gang DPDT Swi t ch

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To Speaker( mount ed on modi fi edHeadphone)

3

5

Inverting Amplifier At this stage, the microphone signal is inverted by 180

degrees and the background noise is canceled.

Overall circuit

Outputs Amplifying the signal

Canceling the signal

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.

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.

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.

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.

Questions ?

THANK YOU