If you’re a commuter or listen to your music in public, there is no better upgrade you can get than noise cancelling headphones. Many people believe that in order to get better sound quality, they need to spend more, but that’s only half right: you need to also prevent noise that could overpower your music from reaching your ears. Plenty of companies have tried their hand at active noise cancelling (ANC) headphones, and a few have become so good at it that it’s one of the main selling points for their wireless headsets. But how do noise-cancelling headphones work? And why is it so cool?

Editor’s note: this article was updated on August 27, 2020, to include information about noise cancelling technology and dizziness. 

Know thy enemy: noise

how do noise-cancelling headphones work BBC

To understand how to cancel noise, it’s important to first what sound is. If you try to visualize sound, you probably picture it in the form of a wave like the one pictured above. Though this 2D illustration will definitely come in handy later, it isn’t entirely an accurate depiction of what sound actually is. At least not until you fully understand what it implies. This is where physics kicks in.

Sound as you hear it is really just the compression and decompression of the particles in the medium in it flows through—for our purposes, we’re talking about air. It may be a little easier to picture sound as a 3D ripple through air. Those moving particles lead to very slight changes in air pressure. We call the measured power of these changes in air pressure amplitude. Your ears and brain detect and decipher those changes in pressure as sound. If you were to chart the amplitude, over time you end up with the wave pictured above. The louder the sound, the more extreme the amplitude.

How your headphones cancel outside noise

Your headphones cancel outside noise by using a trick of physics called “anti-phase.” The concept is simple, but very difficult to get right, as you’ll read ahead.

If you were to take two identical waves and place them on top of each other matching up the peaks and troughs, the two waves are said to be “in-phase” which results in an even larger wave (louder sound). But what happens if you delay one of the waves by exactly one half wavelength matching up the the troughs with the peaks of the other like in the picture below?

Constructive and Destructive Interference

The two waves are then said to be “out of phase” and subtract from one another as the positive pressures of one wave are acting against the negative pressures of the other, and vice versa. Think of it as trying to add one and subtract one. You’re just left with zero. This is the basic physics behind active noise canceling. But how is that used in your headphones?

Tiny microphones

A photo showing the microphone array of the Bose Noise Canceling Headphones 700.

The microphone array (shown here as the holes in the side) records the noise around you to calculate how to cancel it

Headphones make use of this by way of tiny microphones on the outside of your headphones. They listen to the ambient noise around you, and then the onboard electronics take it from there. The headphones then create sound that is exactly opposite to that sound wave (the anti-phase) to cancel it out so that all you should hear is the music coming from your headphones—and not anything going on outside.

Of course this is all theoretical. In practice, noise cancellation is hard to do, and far from perfect. Consistent noises like the low hums of jet engines on airplanes are easier for headphones to recognize and cancel when compared to sudden, random sounds like people talking.

While the physics remains the same, some companies are better at active noise cancelling than others. But now that you know how it works, you can pick the pair that’s right for you.

Can noise cancelling headphones cause dizziness?

A picture of the Panasonic RZ-S500W noise cancelling earbuds both in the case, showing the LEDs on the buds.

The Panasonic RZ-S500W made Lily feel disoriented, because of the high-intensity hybrid ANC technology.

Yes, listeners have reported feelings of dizziness and disorientation when using noise cancelling headphones—our very own Lily Katz included. In some cases, headaches and nausea are also present.

According to an interview with the Wall Street Journal, New York ear, nose, and throat doctor Sarah Stackpole explained that noise cancelling technology may transmit extremely low-frequency vibrations that stimulate balance receptors connected to our ears’ stereocilia, or hearing hair cells. What then happens is that these receptors falsely communicate to the brain that the head is moving, despite one’s eyes being fixed. Mixed messages like this can trick the brain into thinking its experiencing motion and thus, dizziness.

One solution to this for moderately affected listeners is to decrease the ANC intensity. This can be done in many headset apps, or it can be changed directly with the headset’s controls. Another solution is to buy a pair of noise cancelling headphones that aren’t at the top of the class. The sub-optimal noise cancelling may be frustrating or disappointing to others who don’t suffer from side effects, but could prove just right for you. The final solution is to forgo active noise cancelling altogether, which isn’t the best option for frequent flyers but may be the most comfortable.

Next: Sony WH-1000XM4 vs Sony WH-1000XM3

Frequently Asked Questions

Can you use the noise cancelling headphones to give you silence or do you have to play music?

Most ANC headphones will stay on and allow you to enjoy the silence without any signal being applied.