Noise-cancelling headphones do not create perfect silence. Instead, active noise cancellation is especially good at reducing steady, low-frequency sounds such as the rumble of an aircraft cabin or a train.
1. Microphones listen to the surroundings
Small microphones measure outside noise. Some headphone designs also use microphones inside the ear cup to check the sound that reaches the listener.
2. Electronics calculate an opposite wave
The headphones process the incoming sound and produce a carefully timed signal with an opposing pressure pattern. When the original and generated sound waves meet, they can partially cancel one another. This is called destructive interference.
3. The speaker plays music and the cancellation signal
The same speaker system may reproduce your music while also producing the anti-noise signal. The electronics must react quickly because sound changes continuously.
Why do voices still get through?
High-frequency and sudden sounds are harder to cancel because they change quickly and may reach the ear through different paths. Passive isolation from the ear cushions or ear tips helps block some of these sounds.
Key takeaway: active noise cancellation uses microphones and precisely timed sound to reduce certain noises, while the physical fit of the headphones provides additional isolation.