SPECIAL ASSISTANCE PROGRAMME (SAP) WITH THRUST AREA OF "ACTIVE NOISE CONTROL"

Experts discuss noise control and its applications | Chandigarh News - Times of India

This was a project underway at my undergrad school and sponsored by the Ministry of Human Resource Development, Govt of India.

The goal was to implement an Active Noise Cancellation System for a patient lying inside the ambulance. The sound generated by a siren can go as high as 120 dB. Here’s a scale for reference:

Noise reduction can also be achieved using Passive Noise Control techniques which include using tools such as sound absorption surfaces, ear plugs, headsets, etc. Passive noise reduction alone cannot be used for effectively blocking low-frequency sound waves since they cannot be contained easily (that is the whole point, they need to be heard by drivers inside locked vehicles).

Noise cancellation works, at a very low level, based on phase reversal. Below are two screenshots from the simulations we ran:

A sine wave used as the “Noise” signal

The anti-noise signal generated:

Notice how the signal slowly picks up, and adapts to the noise being read. Eventually (in an ideal scenario), the signal matches a perfect reversed noise signal, thus, when combined, will lead to a zero sound output being heard.

This is exactly how Active Noise Cancellation works in the headphones we wear every day.

Here’s a schematic for a single channel system:

Here’s how our test setup looked like for the above schematic.