# Noise Canceling Headphones

By Radim Strnad

Topic: Computing, AI & Electronics

[Open the interactive Jig](https://ask.jig.com/j/iGAGZTOjQFal)

## Guide

### 1. Quiet on demand

These over\-ear headphones can turn a noisy room calm\. They do not just block sound: they fight it with more sound\. Drag anywhere to look around them\.

Noise canceling is often called ANC, short for active noise canceling\.

### 2. Sound is a wave

Every sound is air being pushed and pulled, so its pressure goes up and down again and again\. The red line shows the hum of this fan as a wave: its high points are peaks and its low points are troughs\. Deep hums make long, slow waves\.

Hertz counts how many waves pass each second\. A deep 100\-hertz hum makes waves about 3\.4 metres long\.

### 3. Cushions block the squeaks

Thick, sealed ear cushions stop most high, squeaky sounds on their own\. This is called passive isolation\. The short gold wave dies at the cushion, but the long red rumble still slips through\.

### 4. Tiny microphones listen

Let us cut the ear cup open\. A microphone near the outside hears the noise before it reaches you\. Another one inside, by the speaker, hears what is left near your ear\.

Some headphones use eight microphones in total\. This cutaway is a simplified picture\.

### 5. A chip makes anti\-sound

A tiny computer chip takes the noise and makes its mirror image\. Where the noise pushes, this anti\-sound pulls\. The speaker plays the blue anti\-sound together with your music\.

The chip works in millionths of a second, fast enough to keep up with a hum\.

### 6. Peak meets trough

When a peak of the noise meets a trough of the anti\-sound, they add up to almost nothing\. Turn noise canceling off and on, and watch the white line on the little screen: the sound at your ear\.

Scientists call this destructive interference\.

### 7. Best on steady hums

Canceling works best on steady, low sounds like engines, fans and air conditioners\. Sudden sounds, like a voice or a clattering spoon, change too fast, so a little still gets through\.

It works best on sounds below about 1,000 hertz\.

### 8. Calm in a busy world

Cushions, microphones, a chip, a speaker and a battery work together to calm the roar\. Next time you hear a steady hum, imagine its mirror\-image wave\.

Amar Bose sketched this idea on a noisy flight in 1978\.