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How do noise-canceling headphones work?

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📓 The short answer

Noise-canceling headphones work by using microphones to pick up ambient noise and then producing sound waves that are the exact inverse, effectively canceling out the unwanted noise.

📚 The long answer

Whether or not you own a pair yourself, you've probably heard of noise-canceling headphones.

While it may seem magical how noise fades away, the technology behind noise-canceling headphones has to do with the physics of sound waves.

All the sounds we hear — from a train screeching to birds singing to the cracks of your knuckles — travel through the air as sound waves. The shape of a sound wave depends on its pitch and volume. Higher pitched sounds have higher wave frequencies and louder sounds have taller waves, and vice versa.

Things get interesting when sound waves overlap. Now imagine you're at a choir concert and the choir starts singing the same note. The result is a louder sound. This phenomenon is called constructive interference.

Here's a diagram of two sounds of the same pitch, with aligned peaks and valleys. The result is a taller wave, or a louder sound of the same frequency.

But what if you flipped the other sound wave upside down? That would mean Sound #1's peaks would align with Sound #2's valleys. This is what is known as destructive interference.

When you combine Sound #1 with its exact inverse wave, the result is no sound at all. Active noise cancelation, the core technology behind noise-canceling headphones, relies on this principle of destructive interference.

Here is the step-by-step process of how noise-canceling headphones work:

Step 1: Ambient noise is picked up by the headphones' microphone.

When turned on, your noise-canceling headphones are always listening. Its microphone is picking up on the frequency and amplitude of any noise in your surrounding area, otherwise known as ambient noise. Noises like your neighbor's lawnmower, your fellow airplane passenger's snoring, or the espresso machine at your favorite cafe are all being captured on the mic.

Step 2: A digital signal processor calculates the inverse sound wave of the ambient noise.

Next, the digital signal processor takes the data provided by the microphone and calculates the exact inverse frequency and amplitude of the ambient sound waves.

The "anti-noise" determined by the signal processor is 180° "out of phase" of the incoming sounds. In other words, the inverse sound waves have valleys where the ambient sound waves have peaks.

Step 3: The headphones produce sound waves that "cancel" out the ambient noise.

The "anti-noise" sound wave determined by the signal processor then feeds this into the headphone speakers, along with any music you have playing. The opposing sound waves create destructive interference, canceling out the ambient noise.

When does noise cancelation not work?

Noise cancelation can reduce noise by up to 80 decibels, but it isn't perfect. Sudden, high-frequency, or loud sounds can make it challenging for your noise-canceling headphones' to keep up with producing the inverse sound waves. That's why noise cancelation is best for low frequency, predictable sounds, like the cabin of an airplane.

🧠 Bonus brain points

What is the difference between "noise canceling," "noise blocking," and "noise masking"?

Noise canceling uses destructive interference to eliminate ambient noise by generating opposing sound waves. Noise blocking relies on the physical design and materials of the headphones to muffle sounds. Noise masking produces white noise to drown out ambient noise.

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

📖 Book of the week

​Gratitude by Oliver Sacks​

I haven't read other books by Oliver Sacks, but this one definitely convinced me to add them to my list. Oliver Sacks, a clinician and author, wrote a series of essays close to and during the final months of his life. You get to know an author if they write with honesty and vulnerability – like having a conversation with them. Reading this book was like having a conversation with Oliver who showed profound gratitude and peace with the imminent end of his life. A great reset if life has thrown more than a few challenges your way.

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​Check out the full list of books I've recommended here.

👀 Catch up on other curious questions

• ​Do elevator “Close Door” buttons really work?​​
• ​Why are instruments in different keys?​​
• ​How should you charge your devices to maximize battery life?​​

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