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How Active Noise Cancellation Works

Noisy environments can both distract you and irritate you when you want to work. Headphones with active noise cancellation capabilities can provide respite, but do you know how they work?

SummaryThe Shape of SoundNoise FilteringNoise Cancellation is ComplicatedConclusion

In this article, we discuss how headphones from Bose, Beats, and other brands keep outside noise out of your ears.

The shape of sound

The most important lesson you should learn today is that sound waves follow a regular pattern. A sound wave of any frequency compresses and rarefies (releases compression) molecules as it travels through air. This is comparable to a transverse wave, which looks like the following image.

How Active Noise Cancellation Works

Noise filtering

When unwanted noise occurs, your headphones should use the characteristics of sound waves to start making your world quieter.

Your headphones require a battery to power a built-in microphone that listens for outside noise. The microphone recognizes the different frequencies reaching your ear, then sends that information to its speaker – the same speaker you use to listen to your music.

The speaker then emits additional sound waves to combat the offending noise. It does this by creating destructive interference that uses the peaks and troughs of the waves against them.

In destructive interference, two sound waves of equal intensity and pitch can cancel each other out if they are 180 degrees out of phase. This graph shows what this phase shift looks like.

How Active Noise Cancellation Works

The purple wave is the same wave shown in the first image of this article. The green wave is out of phase with the green wave by 180 degrees.

The two waves now have their crests and troughs aligned, so that their compression and thinning of the air is eliminated. The sum of these two waves is a straight line passing through the center of the chart. Essentially, the combination creates no noise.

Noise-cancellation is complicated

Although calculating the cancellation of a sound wave is easy, the real world is not limited to a single phase annoying noise frequency.

The noise cancellation available in your headphones is a masterpiece of engineering. It should identify all wavelengths, intensities and phases of sound in your environment at all times. Then it must actually generate equal but opposite sound waves in addition to the music or audio you want to hear.

Ultimately, what you receive as noise-canceling audio isn't always perfect. Your headphones should cancel out about seventy percent of outside noise, and they probably won't work well with loud, sudden noises like a baby crying or a door slamming. They will work best when suppressing constant noises such as the murmur of a crowd or the hum of a jet plane.


If you're considering buying a pair of headphones for active noise cancellation, keep their capabilities and limitations in mind.

Now that you know how they work, prepare for less than perfect suppression of unwanted sound, but remain optimistic about how far this amazing technology can actually get you.