十万个为什么·科学启蒙30篇（4）

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为什么耳机降噪能抵消噪声

Noise-cancelling headphones use built-in microphones to detect incoming ambient sound waves.
A tiny processor then generates an 'anti-noise' wave with the exact opposite phase.
When the original noise and anti-noise meet, they cancel each other through destructive interference.
This works best for steady, low-frequency sounds like airplane engines or AC hums.
Higher-pitched noises like voices are harder to cancel because their wavelengths are shorter.
Some models combine this electronic method with physical sound insulation using earcup padding.
Battery power is needed to run the microphones, processor, and speaker drivers continuously.
The result is quieter surroundings without needing to raise music volume dangerously.
Passive noise isolation alone blocks sound physically, but active cancellation adds smart tech.
Both methods together give users clearer audio and better hearing protection over time.