How Do Noise-Cancelling Headphones Work?

Demystifying the magic of ANC

If you’ve spent any time researching modern consumer headphones, you’ve likely come across the concept of noise cancellation. Most consumers understand these kinds of headphones will provide more silence from your surroundings than not wearing headphones, but how does it all work? In this guide, we’ll cover the different ways headphones blot out sound, how the technology works, and how it fits in with your music listening.

How Sound Works

Before getting into the inner workings of noise-canceling headphones, it’s essential to understand how sound works. In essence, any sound you hear is the vibration of air particles that trigger your hearing.

A photograph of a soundwave depicted on a screen in an audio production program

These vibrations are often measured on a graph as a waveform, with frequency denoting the pitch of the sound and amplitude denoting how loud this sound is. This waveform above is a stylized version of a sound, but it will help you to understand how noise-canceling works in a later section.

What Are the Two Different Kinds of Noise-Cancelling Headphones?

One of the most critical distinctions when choosing your pair of headphones is determining whether those headphones offer what’s called active noise cancellation or passive noise isolation. The passive version means the headphones provide a solid seal around or in your ears, and therefore physically block out a degree of outside sound. It can be an effective way to create a pleasant sound stage for your music, but it is not a very efficient method of reducing noise, especially in louder environments like airplanes and train stations,

On the other hand, active noise cancellation uses actual power (typically in the form of an onboard battery) and dedicated microphones to read the sound of your environment and “cancel” that sound out. The headphones use technical intelligence to provide an adaptive amount of noise cancellation and the optimal level of silence, depending on your surroundings.

How Does Active Noise Cancellation Work?

Active noise cancellation uses the natural laws of physics and sound to reduce noise. Remember that waveform from above? If your headphones used their microphones to read that waveform as noise, noise-canceling headphones would produce a small amount of noise at precisely the same amplitude and frequency as the waveform. They would play it “out of phase” (a fancy term for two sounds that are the same but slightly earlier or later than each other). These waveforms then add together and cancel out, much like a positive number and a negative number. This process leaves you with a vacuum-like silence.

Do Noise-Cancelling Block Out All Voices?

Many manufacturers have gotten very good at creating effective noise cancelation, particularly flagship headphones from Apple, Sony, and Bose. While these headphones effectively cancel sustained environmental noises (like the hum of an HVAC system or the rumble of a plane), it’s nearly impossible to suppress irregular sounds like the human voice or loud, sudden thumps.

Because ANC headphones use microphones to read and adjust noise levels, you’ll hear a noted decrease in all sounds around your room (with voices sounding muffled and distant). Still, as the technology stands right now, no headphones offer 100% silence.

Can You Listen to Music With Noise-Cancelling Headphones?

If you’re using active noise-canceling headphones, you may wonder if the minor “out of phase” noise will affect your music. The short answer is “yes,” but there are some practical things to consider. Most audiophiles will tell you using ANC headphones will be detrimental to the purity of your audio.

It's technically accurate, but most consumers won’t notice this, and many premium ANC headphones account for this using clever processing and software on the headphones. In short, your music will sound fine unless you’re extra picky about your headphones, and in most cases, it will sound better because it isn’t competing with outside interruptions.

Is Noise Canceling Bad for Your Ears?

The last point to consider is this concern about whether ANC is “good” for your ears. You may notice an unpleasant sensation with ANC headphones, like when your ears are blocked (on a plane or underwater).

This sensation comes about because your ears are used to hearing a small amount of room noise, and when it’s not there, your brain assumes the air pressure has changed and will likely try to compensate with eardrum regulation. It's why it sometimes feels like noise-canceling headphones are messing with your ear pressure.

Some people find this uncomfortable, and it is true it isn’t ideal for those with sensitive inner ears. But for the most part, this discomfort is all mental, and it is perfectly safe to use ANC headphones.

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