Noise-Canceling Headphones: What They Are and How They Work
Jhett Thompson
Noise-canceling headphones come in handy often: on a long flight, when you need to focus at work or school, when you're listening to tunes, or any time you need the background noise dialed to zero.
The feature has truly changed the headphone experience, and many brands are utilizing the technology and their own versions of the product in a variety of colors, sizes and styles.
But how exactly does this technology work to silence the outside world while playing your favorite music or podcast? John Rule, Ph.D., a research and development scientist for systems and controls at Bose, tells PEOPLE that these headphones use a combination of microphones, mini-computers and competing vibrations to block out ambient noise.
Want to learn more? Ahead, Rule explains what noise-canceling means, how noise-canceling headphones work and if the technology is actually safe to use.
What Noise-Canceling Means
Jhett Thompson
Despite their name, noise-canceling headphones don't actually cancel out outside sound completely. "Noise, both wanted and unwanted, is just a bunch of pressure vibrations that travel through the air from the source — someone talking, a stereo speaker, a car engine — to our ears. But because of physics, we typically can't just block the vibrations," Rule explains
So, how do these headphones keep outside noise out if they're not blocking the sound? "We measure the incoming vibrations before they reach your eardrum, and produce a second set of vibrations from a tiny speaker that are equal and opposite to the incoming sound," he tells PEOPLE. "When you add these two vibrations together, they cancel each other out, leaving behind almost no vibration at all. It's difficult to make this cancellation perfect, so your eardrum will still hear a very small signal, which your brain will interpret as the world being much quieter."
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Types of Noise Cancellation
According to Rule, there are two types of noise cancellation: passive noise cancellation and active noise cancellation.
"Passive noise cancellation simply refers to having something physically blocking your ears to muffle sound," he says, like, for example, your headphones or earbuds.
Active noise cancellation uses another sound (rather than a physical object) to block out noise. The two sounds essentially cancel each other out, making the background noise seem quieter than it actually is.
How Noise-Canceling Headphones Work
Jhett Thompson
As described above, the basic principle is that two opposing vibrations cancel each other out, practically eliminating noise from the outside world. And when it comes to noise-canceling headphones, a microphone is actually used to limit the noise.
"Noise-canceling headphones work by measuring the incoming noise with one or more microphones, calculating the best 'anti-noise' signal, then playing that signal through a little speaker into your ear," he describes.
According to Rule, headphones with two microphones in each ear work the best. "Between the mics and the speaker is a tiny computer that does a bunch of math very quickly — faster than the speed of sound or it wouldn't work — to figure out the anti-noise signal."
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There's a lot more going on behind the scenes to cancel the noise than you might think. It's interesting to note that the speaker in your headphones is actually doing two jobs at once: "The same speaker that is used to cancel the unwanted noise is also used to play music or podcasts, and it does both these jobs at the same time," he adds. "So your noise-canceling headphones cancel the outside world while at the same time playing your favorite songs."
Are Noise-Canceling Headphones Safe?
There is a little bit of controversy as to whether or not noise-canceling headphones are actually safe to use. There have been reports of some people experiencing "eardrum suck" — a phenomenon that feels like pressure in the eardrum. There's no scientific evidence around what may cause this because there's no change in pressure in noise-canceling headphones. Many believe this effect is actually psychosomatic.
Dr. Benjamin Asher, an ear, nose, and throat doctor, tells PEOPLE he's had patients complaining of headaches from their headphones. As far as we know, there aren't any long-term effects from headphones, they just may cause discomfort for certain people.
