This was a semester long team course project as part of the Electronics Design Lab (the dreaded “EDL”) course at IITB. The aim of this project was to build an affordable pair of noise cancelling headphones.
We developed an analogue feedback based controller as a disturbance rejection control system; which had the added benefit of improving the sound quality of our relatively cheap $10 headphones. The main challenges in this project were to characterise the headphone-ear system (the “plant”) to get the frequency magnitude and phase response; as the system changes characteristics based on a number of factors, including the shape of the ear cavity, the way the headphones are worn, and the placement of the microphones inside the headphone cavity.
Our control system resulted in a successful attenuation of noise, with a peak cancellation of 17 db at 100 Hz. We aimed for maximum cancellation at 100 Hz, as that’s the frequency of noise from appliances in an office setting, like fans and airconditioning; when the AC mains supplies power at 50 Hz.
Our system was designed to work at 3 V, that is two dry cells. However, we did not optimise the power consumption to maximise battery life, given the limited time on the project; and because that would mean micro-optimisation before macro-optimisation.