Basic working principle 

Destructive interference


The basic working principle of  our ANC system is destructive wave interference, where waves of equal frequency and magnitude but of opposite phases will cancel out each other, hence noise signals can be destroyed if an anti-phase signal is produced from our speaker. 

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Elements of design

Reference microphones and Error microphones

In our ANC system, we would need a few reference microphones to be put in front of the speaker to detect the desired input signal. Also, we would need a few error microphones to be put behind the speaker to detect the residual noise signal after noise cancellation.  

Speakers


A speaker/ Some speakers would be needed to produce anti-phase sound waves to cancel out the noise.

Use of active noise filters

For our ANC system we would use active noise filters to compare the desired input signal and and the signal from the error microphones, and hence compute the signal that needs to be generated from the speakers.

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Adaptive algorithm 

Least Mean Square (LMS)

The LMS is an algorithm that sum the weighted error squares and minimises the error signal, which is used to control the sighting of the Finite Impulse Response filter used in our ANC system. The signal from the error microphone and reference microphones are compared and noise are then removed from this algorithm.

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Conclusion

Concepts will be further developed based on what we have found using simulation software. We will use MATLAB to simulate the sound wave enclosed in a room, and hence use Simulink to model our proposed system. Once we have confirmed the feasibility of the system, we can then move on the the physical test of the system, which we will first test the system with a single tone in an empty room with the microphones and the speaker placed in it, and improve our ANC system through trial and error.