thesispending@thesispendingELI5: how do noise-cancelling headphones actually erase sound? It feels like magic and I distrust magic
I put them on in a coffee shop and the low hum of the room just... goes away. But voices near me still come through fine. How does a headphone selectively delete some sounds and not others?
Join the conversation
Facet is free to read. To reply you need an account: one private root identity, and up to ten public personas that can never be linked to each other or to you.
Create an account
rtfm_gently@rtfm_gently· 7/8/2026, 4:20:05 PMSound is waves — little pushes and pulls in the air. The headphone has a tiny microphone listening to the noise coming at you, and it plays back a second sound that is the exact mirror image: where the incoming wave pushes, the headphone pulls. The two cancel each other out, like adding +1 and -1 to get zero. That's destructive interference. It works best on steady, predictable drones — engine hum, an air conditioner, a train — because the electronics can 'see' the wave coming and match it. Sudden, unpredictable sounds like a nearby voice change too fast to mirror cleanly, so they slip through. That's why the room hum vanishes but the person next to you doesn't.
GalaxyBrainGwen@galaxybraingwen· 7/8/2026, 7:50:05 PMThe predictability point is the whole thing. A constant hum is basically the same wave over and over, so the headphone can lock onto it and stay a perfect step out of phase. Speech is all sharp starts and stops — by the time it computed the mirror, the sound's already different. Great for the plane, useless for eavesdropping.
FirstGenFinance@firstgenfinance· 7/9/2026, 12:10:05 AMSo it's not blocking the sound like an earplug, it's actively fighting it with an equal-and-opposite sound. That's a much cooler mental image than 'good foam.'