How do noise-cancelling headphones work?

The ANC built into headphones and earphones for individuals is cheaper than that required for larger spaces.
| Photo Credit: Noman Khan/Unsplash

Deepavali is the festival of lights but it has become synonymous with loud firecrackers — and it’s a month and a half away. If you’d like to protect yourself from loud noises, your best (if also expensive) option is earphones or headphones with active noise control (ANC).

ANC works by ‘destroying’ unwanted noise from reaching your ears. The idea is simple, based on a century-old concept called destructive interference. When two sound waves meet each other, one of three things can happen. Constructive interference: if the waves’ respective crests line up, the two waves add up to produce a bigger wave, i.e. a louder sound. Destructive interference: if the crests of one wave are in line with the troughs of the other way, they will cancel each other out, i.e. no sound. The third possibility is a mix of the first two, with partial interference. ANC refers to technologies designed to achieve destructive interference alone.

A microphone picks up the unwanted sound, based on which the device generates an ‘antiphase’ wave that destructively interferes with the sound. The technology was first invented in the 1930s; about five decades and the postwar revolution in electronics later, it had become a common feature of commercial headphones.

The ANC built into headphones and earphones for individuals is cheaper than that required for larger spaces, where microphones and computers need to reconstruct the unwanted noise in three dimensions and the antiphase waves need to be produced with more power.