How Do Noise-Canceling Headphones Work?

October 1, 2015 | Kelly Tatera

Noise cancelling headphones worn by a red head
Photo credit: Jonathan Grado/Flickr/CC BY-SA 2.0

Because tuning out crying babies on airplanes is important.

Whether it’s the roar of an airplane engine or the buzz of people chatting on the subway, ambient noise can be a buzzkill when you’re trying to savor the new album your favorite artist just dropped. Thanks to companies like Bose and Beats by Dre, the annoying cacophony of the world can be tuned out with noise-canceling headphones. But how do the headphones seemingly make noise disappear?

SEE ALSO: Virtual reality turns  your city into a game board

First, it’s the shape of certain earbuds and headphones that helps block out ambient sounds by physically preventing sound waves from reaching your ears. “Noise-isolating” accessories work in one of two ways — creating an external seal around the ears or using sound-absorbing material, like high-density foam. Some earbuds just simply better fit to the shape of the ear canal, but overall, “noise-isolating” products can block up to 20 decibels of sound.

That’s enough to block out some noise in the atmosphere, but it’s certainly not enough to drown out the bloodcurdling roar of unhappy babies. That’s when noise-canceling headphones save the day with active noise control (ANC).

Amar Bose, MIT graduate and founder of the Bose Corporation, laid the groundwork for ANC technology. Instead of simply blocking outside sound waves, ANC actually uses “destructive interference” to cancel out noise — meaning it creates its own sound waves to cancel out the incoming ones.

At first the concept doesn’t seem to add up. How does adding more sounds to the air result in silence? The phenomenon is possible only because sound is a wave with cycles of peaks and valleys. ANC technology detects sound waves in the air and then produces the equal and opposite effect more or less simultaneously — for every peak, it produces a valley, for every valley, it produces a peak. The resulting wave is more or less a flatline: silence. This adds an extra level of noise reduction by erasing the lower-frequency sound waves.

As for blocking sound waves of higher-frequency? The isolating structure of ANC headphones already takes care of that.

On average, noise-canceling headphones can block up to 80 decibels of sound. According to the National Institute on Deafness and Other Communication Disorders (NIDCD), long and frequent exposure to sounds over 85 decibels can cause hearing loss.

No matter what, some peace and quiet is good for the soul. And at the very least, it’s essential to have the ability to alleviate the horrendous combination of public transport and small children.

Hot Topics

Facebook comments