The Hows and Whys of Noise Cancelling Headphones

By Lauren Dragan

Headphones provide listeners the rare opportunity to shut out the world and immerse themselves in music. But when the world is a little noisier than usual, that can be tough to accomplish. That’s where noise-cancelling headphones come in. But what’s the difference? How do they work? Let us guide you through the basics.

Most headphones block out external sound either by covering the ear with a solid cup or by plugging the ear canal. This helps to prevent some of the noise around the listener from reaching the eardrum by mechanical means. This method is often referred to as “sound isolating technology.” Depending on the materials used and the fit of the headphones, some models do a better job of blocking out noise than others. But regardless of how well-designed a chassis is, this often adds bulk or still allows some sound to seep through and be heard.

Active noise-cancelling (ANC) headphones work differently. ANC uses a principle of physics called “destructive interference” to remove low frequency noises from around your ear. Sound, as you might remember from school, travels in a pattern much like waves in water. Each frequency has a unique pattern of up and down that flows through the air and bounces off the eardrum. And like water molecules, air molecules are pushed up and down along the sound waveform. But if two equal-frequency sound waves reach the same space at the same time, they cancel themselves out, and the molecules don’t move.

Active noise-cancelling headphones exploit this phenomenon by putting a microphone on the headphones. This microphone processes the sound around the listener, and then creates an exact opposite waveform to the external noise and produces it in the earpieces. This waveform collides with the external sound’s waveform and cancels it out. The result? Silence.

What this means in a practical setting is that instead of being forced to listen to content at high volumes to drown out low frequency noise, you can keep your volume down to safe levels. Not only does this save your hearing, but it also frees you from distractions and keeps your focus where it belongs: on your music. Whether plane engine hum, subway din, or the drone of fans and office HVAC systems, ANC technology helps to remove the distractions to create your own personal sonic oasis.