True Quiet

How Do Active Noise-Canceling Headphones Work?


March 13, 2018 Tech By Photo by Chase Pellerin

We review a lot of active noise-cancellation (ANC) headphones and for good reason. They’re among the most popular types of headphones and they come in over-ear or in-ear models. They block out ambient noise: turn on a pair and you hear almost nothing. It’s serenity at the touch of a button — pretty darn cool, especially if you’re a frequent traveler or work in a noisy office.

Today, there a lot of really excellent wireless ANC headphones, made by companies such as Sony, Sennheiser and Bowers & Wilkins, but the gold standard is still made by Bose. The company’s first QuietComfort series of active noise-canceling headphones first hit shelves and set the bar in 2000; over the years, they have remained top. The company’s latest QuietComfort headphone, the Bose QC35 II, is the QC series’s best in all categories: best noise-cancellation, sound quality and overall comfort. It’s also wireless, like its predecessor, the original QC35 (Series 1), and is integrated with Google Assistant allowing users to make calls, get directions and ask questions (like, “What’s the next meeting on my calendar?”) without taking out a phone.

Back on track — how are active noise-canceling different from other headphones? For starters, “active” implies that the headphones have a built-in battery, which they use to create their own sound waves that counter, and therefore cancel out, the noise outside of the headphone. To accomplish this, all active noise-canceling headphones have miniature microphones that are built into each earpiece. These microphones listen to ambient noises and then electronically generate new sound waves that are the exact opposite to those ambient sound waves — called an antiphase — which in effect “cancels” out both sets of sound. Because of the mechanics behind the technology, if ANC is switched on when you’re wearing the devices, you’ll feel a pressure against your ears similar to driving through a tunnel or reaching a certain in-flight elevation.

If the headphones aren’t playing music and you’re in a noisy environment, the active noise-canceling tech makes it sound like you’re in a quiet, empty room. Quiet. Additionally, ANC makes it easier to listen to music. When wearing passive headphones amidst ambient noise, your brain has to work hard to prevent it from interfering and distracting you from the music. Because ANC actually reduces the amount of sound that you hear, it is, overall, easier on the brain and, in theory, makes listening to headphones a more pleasant experience.

Frequently Asked Questions

Do active noise-canceling headphones block out all sound? The answer is no. Even the best active noise-canceling headphones have trouble blocking out everything. Noises that are consistent, like the engines of cars or airplanes are much easier for ANC headphones to block out than abrupt noises, like somebody talking directly to you or a loud bang. The latter are more difficult for the headphones’ mics to pick up and process quickly.

How does noise cancellation impact sound quality? You might have guessed, but active noise-canceling doesn’t have a positive effect on the overall sound quality. It creates a slight background “hiss” over all your music, meaning songs and podcasts won’t sound as natural. For audiophiles and people who want the best possible audio quality, a high-quality pair of passive over-ear headphones are probably the best bet. This is why, when the ANC is turned off on over-ear headphones, like the Bose QC35 II or the B&W PX, their sound quality improves.

Passive vs active noise cancellation — what’s the difference? Because noise-canceling is a hot trend in the headphone industry, you’ll see headphones marketed as “noise-canceling” headphones that really aren’t at all. Passive noise-canceling or noise-isolating headphones naturally block out ambient sounds because of the shape and fit of their earpads. Active noise-canceling headphones use mics that actively seek and cancel out ambient sound frequencies. There’s a big difference.

In-ear vs over-ear? There are over-ear and in-ear active noise-canceling headphones, but generally, in-ear ANC headphones aren’t as good at noise-canceling. The reason is that over-ear ANC headphones combine active microphones with the natural shape of the headphones that naturally (aka passively) block out ambient sound. In-ear headphones can passively block out sound, too, but the earbuds have to fit really snug in your ear canals to be very effective.

Bose QC35 II Review: The Best Noise-Canceling Headphones Yet

The Bose QC35 IIs offer the same best-in-class active noise-canceling as the QC35s, but add Google Assistant. Read the Story