How do noise-cancelling headphones work?

Noise-cancelling headphones work by using a process called destructive interference to neutralize unwanted sounds before they reach your ears.

Here is how the process works:

1. Microphones pick up sound: Tiny microphones on the outside of the headphones constantly monitor ambient noise (like the hum of an airplane engine or traffic).
2. Sound waves are analyzed: The headphones' internal electronics analyze the frequency and amplitude of that ambient sound instantly.
3. Anti-noise is created: The headphones generate a "mirror image" of the sound wave—a sound wave that is exactly the opposite of the noise.
4. Cancellation: When the sound wave of the outside noise and the sound wave of the "anti-noise" meet, they collide and effectively cancel each other out. Because the peaks of one wave match the troughs of the other, they turn into silence (or a significantly reduced hum).

A few things to note:

• Active vs. Passive: This process is called Active Noise Cancellation (ANC). "Passive" noise cancellation is simply the physical design of the ear cups—the padding and seal that block sound from entering your ear naturally.
• Best for constant sounds: ANC is most effective against low-frequency, consistent sounds like airplane cabins or air conditioning units. It is less effective at blocking sudden, irregular noises like human voices or a baby crying, because those sounds are harder for the processor to predict and mirror in real time.