# 降噪是怎么工作的：用更多的声音对抗噪音

> 降噪耳机并不挡住噪音：它们加上一道正好相反的声波，两者相加几乎归于安静。耳罩外的麦克风听到噪音，芯片把它翻转，扬声器播放出来，只有几十微秒的时间；耳罩内的麦克风再修正剩下的部分。一支 49 秒的科普短片，每个数字都有出处。

- URL: https://oliverz.dev/zh/videos/noise-cancelling
- Author: Oliver Zhang (https://oliverz.dev)
- Language: zh-Hans
- Published: 2026-11-01
- Tags: audio, how-it-works, explainer
- Video: https://www.youtube.com/shorts/aywLhNwXALU

> **一句话总结：** 降噪耳机并不挡住噪音，而是再加上更多的声音。声音是一道高低起伏的压力波；加上和它正好相反的波，在它高的地方变低，两者就会相互抵消，几乎归于安静。耳罩外的麦克风先听到噪音，芯片把它上下翻转，扬声器播放这道镜像波，这一切都要在噪音本身到达耳朵之前的几十微秒内完成。耳罩内的第二个麦克风检查还剩下什么，并加以修正。正是这场赛跑，让降噪对持续的低沉嗡嗡声效果最好，对人声和突然的声音则差得多，这些只能靠耳垫去挡。

## 用声音对抗声音

BBC Science Focus："Noise-cancelling headphones cancel out unwanted sound by creating an opposing sound wave that mimics the noise you want to get rid of, but just 180° out of phase. This means that when one sound wave is at its highest peak, the other is at its lowest, effectively cancelling each other out. This is known as 'destructive interference'."（降噪耳机消除不想要的声音的方法，是制造一道模仿你想去掉的噪音的反向声波，只是相位相差 180°。也就是说，一道声波在最高峰时，另一道正在最低谷，两者实际上相互抵消。这叫作"相消干涉"。）

## 高压遇上低压

The Physics Classroom："Sound is a pressure wave that consists of compressions and rarefactions."（声音是一种由压缩和稀疏组成的压力波。）压缩是 "a high-pressure region"（高压区），稀疏是 "a low-pressure region"（低压区）。当两者正好对上时："The tendency of the compression to push particles together is canceled by the tendency of the rarefactions to pull particles apart; the particles would remain at their rest position as though there wasn't even a disturbance passing through them."（压缩把粒子挤到一起的趋势，被稀疏把粒子拉开的趋势抵消了；粒子会停在静止位置，就好像根本没有扰动经过它们。）于是 "two sound waves would combine to produce no sound."（两道声波合在一起，就不会产生声音。）

## 听到它，翻转它，播放它

还是 The Physics Classroom："Such earphones capture sound from the environment and use computer technology to produce a second sound wave that one-half cycle out of phase."（这种耳机捕捉环境中的声音，再用计算机技术产生第二道相差半个周期的声波。）

BBC Science Focus 讲到其中的部件："First, there is a microphone on the earcup to listen out for annoying external sound."（首先，耳罩上有一个麦克风，用来收听恼人的外部声音。）接着 "the 'out-of-phase' sound is created and then fed into the headphone speakers, along with the music you're playing."（生成"反相"的声音，再和你正在播放的音乐一起送进耳机的扬声器。）

## 几十微秒的赛跑

IEEE Spectrum（2018）："having microphones located so close to the ears means commercial headphones get just tens of microseconds to process incoming sound, calculate an antinoise signal, and play it through their speakers before the sound reaches the ears."（麦克风离耳朵这么近，意味着市售耳机只有短短几十微秒，要在声音到达耳朵之前处理传入的声音、算出反噪声信号，并通过扬声器播放出来。）

在 20 °C 的空气中，声速是 "v = 343 m/s"（The Physics Classroom）。以示意的 2 厘米来算，噪音穿过耳罩大约需要 58 微秒（我们自己算的：2 cm ÷ 343 m/s；没有任何来源给出耳罩的深度）。

## 第二个麦克风检查剩下的部分

SoundGuys："With feedforward technology, the noise-capturing microphones are placed on the outside of the headphones."（采用前馈技术时，捕捉噪音的麦克风放在耳机外侧。）以及："With feedback ANC, the microphone is located inside the ear cup"（采用反馈式 ANC 时，麦克风位于耳罩内部），所以 "You can think of feedback ANC as a self-correcting mechanism."（你可以把反馈式 ANC 看作一种自我校正机制。）混合式 ANC 则 "combines both feedforward and feedback microphones and processing"（结合了前馈和反馈两种麦克风及其处理）。

## 对持续的嗡嗡声最有效

时限也就是极限。IEEE Spectrum："Such a tight computing deadline limits the performance of most active noise-cancellation technology, setting an upper limit on the frequencies it can actively cancel. This requires many headphones to shield the wearer's ears with sound-absorbing materials for higher frequencies."（如此紧迫的计算时限限制了大多数主动降噪技术的表现，给它能主动消除的频率设了上限。因此，许多耳机需要用吸音材料为佩戴者的耳朵挡住较高的频率。）在它 2018 年的报道中，一款高端耳机的 "active noise-canceling range of 0 to 1 kHz"（主动降噪范围为 0 到 1 kHz），并依靠 "passive soundproofing material to dampen sounds in the 1- to 4-kHz range"（被动隔音材料来减弱 1 到 4 kHz 范围的声音）。

SoundGuys："Active Noise Cancellation (ANC) systems work best on droning sounds that are constant in frequency and intensity. Because quick, irregular sounds like music sounds and people talking are over with long before your headset can calculate how to cancel them, the only noise attenuation your ANC headset will offer against annoying coworkers/TV noise is simply what sound they can physically block out."（主动降噪（ANC）系统对频率和强度都恒定的嗡嗡声效果最好。由于短促、不规则的声音，比如音乐声和人说话，在耳机算出如何抵消它们之前早就结束了，所以面对恼人的同事或电视噪音，ANC 耳机能提供的降噪，只是它们在物理上能挡住的那部分声音。）

BBC Science Focus："It works best with lower frequencies, like transport noise"（它对较低的频率效果最好，比如交通工具的噪音）。

## 接近安静，而不是完全安静

SoundGuys："you won't ever see 100% cancellation"（你永远看不到 100% 的消除）。BBC Science Focus："while it can't erase unwanted sound entirely"（虽然它无法完全抹去不想要的声音）。

## 结论

1. 降噪是用声音对抗声音：相反的声波相加，几乎归于安静。
2. 这是一场赛跑：在噪音穿过耳罩之前的几十微秒内，听到、翻转、播放；耳罩内的麦克风再修正剩下的部分。
3. 所以它对持续的嗡嗡声很有效，对人声和突然的声音则较弱：这些要靠佩戴的贴合度和耳垫。

## 来源

- BBC Science Focus，[How do noise-cancelling headphones cancel sounds?](https://www.sciencefocus.com/science/how-do-noise-cancelling-headphones-cancel-sounds/)，2020 年 10 月 18 日
- J. Hsu，IEEE Spectrum，[New Wireless Noise-Canceling Tech Is Faster Than the Speed of Sound](https://spectrum.ieee.org/noisecanceling-techs-edge-is-faster-than-the-speed-of-sound)，2018 年 9 月 5 日
- C. Thomas，SoundGuys，[Active noise canceling (ANC) technology types explained](https://www.soundguys.com/noise-canceling-explained-28344/)，2025 年 10 月 16 日更新
- The Physics Classroom：[Interference and Beats](https://www.physicsclassroom.com/class/sound/Lesson-3/Interference-and-Beats)、[The Speed of Sound](https://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound)

视频用代码制作动画，脚本在 AI 辅助下撰写；上面每条引文都对照出处核实过，标注"我们自己算的"的 58 微秒是我们自己的计算，基于示意的 2 厘米。示意部分：波形、耳罩的剖面图和其中的部件、2 厘米，以及耳机。0–1 kHz 和 1–4 kHz 这两个范围来自 2018 年报道的一款高端耳机（IEEE Spectrum），并非所有耳机。视频为英文旁白。视频用 [Shotloop](https://oliverz.dev/zh/products/shotloop) 制作：我做的免费 Mac 应用，用代码做科普短视频，一个镜头一个镜头地改。