Noise Canceling Headphones: What Is It And How Does It Work?

With sound against sound: ANC is better than earplugs
How you can easily imagine sound
The technology of noise-canceling headphones: Wellenberg meets Wellental
What does noise canceling sound like?
Is noise canceling harmful to health?
List: headphones with noise canceling

With sound against sound: active noise canceling (ANC) is better than earplugs

Numerous manufacturers offer actively noise-reducing headphones - both classic on-ear headphones with a strap and compact in-ears for plugging in. The models are usually a bit more expensive than conventional headphones and either additional batteries, a built-in rechargeable battery or a connection via Lightning or USB Type-C are required. So technology obviously uses electricity to create silence. The technical basis for active noise suppression is the counter- noise principle. That means: Sound is actively "fought" with sound. In contrast to earplugs, which are simply inserted into the ear and block the sound by means of insulation - this is a passive process.

What does the sound look like that we can hear as sound, music, speech or noise? A vibrating guitar string is a good example: here we hear the sound generated and also see what it produces. What we hear is the vibrating movement of the string, which is transmitted to the surrounding air and reaches the human ear in the form of the vibration. The brain interprets these fine vibrations as sound again. So we can perceive vibrations - or more precisely, pressure and density fluctuations in the air - as sound.

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Noise canceling explains: how you can easily imagine sound

Unfortunately we don't see the sound when it travels from the instrument through the room to our head - so how can you imagine it? The term "sound wave" gets to the point, it is a wave that is transported by the air and that is constantly increasing. You already know this from somewhere else: If you throw a stone into a pond, you can wonderfully observe how the waves generated spread out. They look like bigger and bigger rings from above and from the side like a regular pattern - an ups and downs of mountains and valleys. A single wave always has a highest and a lowest point.

The technology of noise-canceling headphones: Wellenberg meets Wellental

You throw the stones away from each other in the same pond. What happens when two waves meet? The wave rings spread out, meet in the middle and … - What is taking place cannot be said in general, because it depends on the exact time.

A particularly high wave crest could form if the moment is right and two wave crests add up.
If two wave valleys unite, then a particularly deep valley is formed.
The third case is the basis for active noise reduction: a wave crest meets a wave trough and both cancel each other out. This is known from mathematics: +1 and -1 add up to 0. Transferred to sound, this means that if two uniform sound waves meet at the right moment, they can cancel each other out and there is silence. In this case, natural science, more precisely: physics, speaks of destructive interference.

A wave crest and a wave trough meet and neutralize each other

Noise canceling is all about timing

Noise-reducing headphones work on this principle and are therefore equipped with microphones. These permanently absorb the noises from the environment. The built-in electronics process these signals at lightning speed - the faster, the better: it reverses the sound waves, an opposite-polarity signal is generated and passed on to the headphones and "mixed" with the music, if you are listening to them. If this anti-sound hits the eardrum at the same time as the original signal - i.e. the actual ambient noise - then they cancel each other out and you hear … nothing.

Active Noise Canceling (ANC): The ambient sound (red) is neutralized by an opposite polarity signal (green)

So the noise-canceling headphones not only have to be able to play music, they also have to create an opposite polarity image of the ambient noise and mix it in with millisecond precision. The better it all works, the stronger the noise reduction effect.

Noise canceling: how does that sound?

Active noise canceling is particularly suitable for switching off low frequencies. The technology can show its strengths when it comes to monotonous hum in an airplane. In fact, the principle also comes from aviation, where pilots have the problem that engine noise drowns out radio communications. With active noise cancellation, you can clearly understand the voice of the person you are talking to in the headset and you don't have to turn it up so loud.

In an experiment we recorded for you how strong noise canceling is (it's best to put on headphones when you watch the video):

Test: Noise Canceling is so quiet

At high frequencies, the method is less effective due to interference, and the principle works less well even with very loud noises. Something else helps there: The shielding by a good fit and complete closure of the ear. As with hearing protection on the construction site: the noise of the jackhammer does not get through to the ear, the energy of the sound wave apparently fizzles out at the hearing protection housing. What is physically correct is that it is converted into thermal energy. When good passive shielding and effective active noise canceling are combined, the noise-reducing headphones are particularly good.

Purchasing advice on the topic:

The best noise-canceling headphones: Over- and in-ear models with noise cancellation

But even the best model cannot ensure absolute silence, for this you would have to measure each ear individually and adapt the electronics accordingly. Part of the ambient sound is also picked up by the skull and transported to the eardrum. The headphones cannot intercept and hide them. Anyone who experiences active noise canceling for the first time will still be amazed. You can still perceive your surroundings - but much more quietly, as if you had closed a door behind you. Then add music and the experience is perfect.

Is noise canceling harmful to health?

Can noise-canceling headphones harm health? No, the opposite is the case, as Dr.-Ing. Hannes Seidler (Dresden University of Technology, Medical Faculty Clinic and Polyclinic for Otolaryngology Ear Research Center Dresden) explained on our request. Here is his detailed answer: