Noise Canceling Headphones Team Members Doan Thanh Khiet Tran Jasmine Khadem Kalina Guentcheva.
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Transcript of Noise Canceling Headphones Team Members Doan Thanh Khiet Tran Jasmine Khadem Kalina Guentcheva.
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
OffPage1Off Page1
Out put of St age 1( Pr e- amp and hi gh pass fi l t erResponse ~ 30Hz- 20KHz @30dB)
4
0
2
OffPage2
Off Page2
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
Off Page2
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