Silence at the touch of a button: how does ANC work?

Dayan Pfammatter

23/11/2025

Translation: Elicia Payne

Active noise cancelling (ANC) is one of those things practically every owner of headphones uses. But how is it that headphones actually dampen noise better than they’re physically capable of doing? How does anti-noise work?

It’s Monday morning, precisely 08:43. I’m on the tram, on my way to work. In front of me a young couple argue loudly, behind me a baby cries just as loudly. Yet I can’t hear a thing – well, barely. Fortunately, I’ve got my active noise cancelling headphones on which reduce the noise around me. All I can hear is Tame Impala’s new album Deadbeat.

Headphones with ANC are everywhere these days. There’s a good chance you’re wearing some on your head or in your ears as you read this.

Active noise cancellation is practically a by-product of new headphones now – and it’s become quite effective, too. It already feels like a bog-standard feature, but the technology behind it is far from dull.

The pioneers of ANC headphones

Before we carefully dissect how the whole thing works, let’s go back to the origins of ANC. As is so often the case with technological developments, noise cancellation initially arose from an industrial need. More specifically, from aviation.

Anyone who’s ever sat in an aeroplane with ANC headphones will already know why. The technology used for sound cancellation is particularly effective for low, constant background noise – such as engine noise from aeroplanes and helicopters. Long before Sony and the like brought the first ANC headphones to the mass market, the technology was developed for pilots. It was an effective way of protecting their ears from the constant noise in their working environment.

But why exactly is the technology so effective?

How anti-noise ensures silence

The theory behind active noise cancelling can be summed up in one word: anti-noise (page in German). Or perhaps «reverse noise» would be more apt.

A simple way of understanding how this acoustic method works is by imagining a sine wave for a simple, constant tone. The higher the waves go, the louder the sound; the more waves there are, the higher the pitch. To get rid of this sound, «destructive interference» is used.

If the wave of the sine note curves upwards, we allow an identical sound from another source – your headphones – to curve downwards and vice versa. The inverted sound cancels out the original source, so that in the best case you don’t hear anything.

However, since noise rarely consists of a consistent sine wave, your headphones must constantly analyse the background noise of your surroundings and adjust the anti-noise accordingly. This is why all ANC headphones are equipped with several microphones and special ANC chips that make noise cancelling possible in the first place. Essentially, this is the Achilles heel of the technology.

What ANC can’t (yet) do

Even if the technology sounds a bit like sorcery, the reality isn’t quite so magical. Let’s think back to the pilots and ANC on a plane. The low hum of the machine is the perfect environment for active noise suppression. It’s a deep, constant sound that doesn’t come towards you from a single direction. This makes it comparatively easy to produce a constant anti-noise.

Things become more difficult with irregular, high-pitched noises. A crying baby in the tram, voices and clinking dishes at the cafe – in these cases your headphones essentially have to react in real time in order to generate suitable counter-sound.

In recent years in particular, however, there have been noticeable improvements thanks to more powerful, faster hardware. This comes in the form of chips: Sony, Bose, Apple and others all have headphones with chips that can even measure, analyse and counteract high-frequency, impulsive noise within milliseconds.

But if you want completely blocked out noise, you also need to consider passive noise suppression. In other words, how well can headphones physically shield your ear canal from the outside world? That is, without any electronic bells and whistles.

Over-ear headphones have pretty much always been a favourite, as they completely enclose your ear. In-ears in the classic wired headphone design are simply placed in your ear in front of the ear canal. And yet (hot take incoming)...

in my opinion, Sony’s current in-ear headphones have by far the best active noise cancelling of all headphones.

Headphones

−7%

EUR208,02 was EUR224,59

Sony WF-1000XM5

ANC, 8 h, Wireless

1010

Sony – alongside Bose – has been at the forefront of ANC for years. The advantage of the Sony WF-1000XM5 is that they also come with foam tips instead of the usual silicone tips. In addition to the high-performance Sony ANC, you have a strong seal in your ear too. They’re like earplugs, but with loudspeakers. And in my opinion, no over-ear headphones have been able to trump these yet.

Loudspeakers are also capable of anti-noise

In fact, active noise cancellation isn’t only used in your AirPods. Active sound suppression can also be used at large events or concerts, for example, to regulate noise pollution for the surrounding area. To do so, large loudspeakers are simply directed towards the stage, reproducing the signal with reversed polarisation.

Harman Kardon also uses this in a similar way with HALOsonic. The interior damping system from Samsung’s audio subsidiary provides a more pleasant driving experience in various vehicles by reducing vibrations with inverted sound waves.

In theory, you can even recreate the effect of destructive interference at home with two old loudspeakers. If you still have a classic stereo system, you can swap the red and black cables on one of the two speakers to create a phase rotation of 180 degrees. If you now point the two speakers towards each other, it should at least become slightly quieter, as the two sound sources will cancel each other out. Or you could simply put your ANC headphones on.

Dayan Pfammatter

Freelance Editor

pf.dayan@gmail.com

I've been fascinated by all things keys, displays and speakers for basically as long as I can remember. As a journalist specialising in technology and society, I strive to create order in the jungle of tech jargon and confusing spec sheets.

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