How Noise-Canceling Headphones Work: The Physics of Silence

The best invention since online shopping for introverts and perfect for tuning out the relentless yappers at the library, noise-cancelling headphones are the main cause for increasing deafness in the new generation and with good reason. Using them as I write this while I blast One Direction, this blog will go over the basic physics principles that explain Active Noise Cancellation (ANC) and the technology that enables it.

Sound Waves

If you also got extreme satisfaction from the viral clip of the crowd at the Grammys singing with a perfect pitch in unison to “Pink Pony Club”, then you understand how different sound sources can interfere. Sound travels in waves; different oscillations represent different sounds. When two or more of these oscillations meet, they combine and form a new wave pattern. Depending on whether the waves are out or in phase, this resultant wave can have a lower or higher sound intensity. Constructive interference is the reason the crowd of singers at the Grammys form a lovely and louder final sound wave.

Noise-cancelling headphones use this core concept for their technology. They identify the incoming sound waves from the background to create exact out-of-phase waves that cancel them out.

Image: https://www.zdnet.com/article/how-do-noise-canceling-headphones-work/

ANC Technology

Active Noise Cancellation (ANC) aims to minimize external and unwanted sound. It uses small microphones to pick up background noise and Digital Signal Processing (DSP) units to analyze them, determining exact properties like amplitude and frequency. The DSP generates artificial sounds with opposite phase waves of the incoming noise [1]. The inverse wave is played through the headphones’ speakers, where it meets the original external noise and cancels it out through destructive interference, significantly reducing the sound level perceived by the listener.

Image: https://www.soundguys.com/noise-canceling-anc-explained-28344/

References:

[1] SoundGuys. (2023). Noise-Canceling ANC Explained. Retrieved from https://www.soundguys.com/noise-canceling-anc-explained-28344/