Everyday we experience loud sounds, especially those who live in the cities, and without appropriate protection, such as noise cancelling headphones, these loud sounds can damage our sensitive inner ear structure, which causes dangerous disease called noise-induced hearing loss.

Have you ever listened to the music in extremely noisy conditions, e.g. in the plane or in metro? If so, there’s no need to explain you what kind of unpleasant experience it is. It’s impossible to listen to the music, or audiobooks under these conditions. Oh, come on – even to find yourself in such noise is unbearable! No wonder that the noise is considered as one of the negative factors of impact on the human health.

To prevent this, one smart guy, whose name is Amar Bose, began to think about the ear protection from the harmful noise impact. During one flight in 1978 he discovered that enjoying music in the traditional headphones to the accompaniment of the airplane jet engines is absolutely impossible. So he began to think how to solve this problem and came up with idea of what we today call noise cancelling headphones. By the way, Bose once told that almost all his ideas came to him unexpectedly.

In order to understand how noise reduction headphones work, firstly, let’s consider how such headphones work. In general, all the headphones can be divided in 3 types by the style they are performed in.

1. In-ear headphones, which are put into the ears. They are the smallest one, and that makes them comfortable to use with portable devices.
2. Supra-aural headphones, or on-ear headphones, which don’t fully cover the ears, but «sit» on them.
3. Circum-aural headphones, which fully cover the ears.

Depending on the way of noise reduction, headphones can be passive or active. Passive noise reduction is provided by the material, the headphones are made of. It goes without saying that bigger headphones mean better passive isolating capabilities, that’s why circum-aural headphones are the best passive noise cancelling headphones.

So how do active noise cancelling headphones work?

Active noise reduction is based on erasing or deleting unwanted sound signals. The headphones have special additional components, which, working together, create an identical to the incoming signal sound waves, but with a 180-degree phase inversion. The resulting sound wave interferes with intruding one (often a noise) and they cancel each other due to the phase inversion. Notice that the amplitude and the frequency of both sound waves are absolutely the same – the only difference is the phase.

Also worth saying that active noise cancelling headphones provide passive noise isolation as well.

As it was mentioned above that active noise cancelling headphones have additional components including microphone, noise canceling circuitry and the battery. All of them are placed inside of the ear cup.

The microphone is used to determine the waveform of intruding signal, which is can’t be erased using passive isolation.

Then, the electronic noise-canceling microcircuit using the information from microphone creates an identical sound wave with the same amplitude and frequency, but inverted phase.

After this, the designed “killer” waveform is fed into the standard headphones speakers interfering with incoming noise, which results in silence and have no influence on the audio from the speakers.

And the last one component – the rechargeable battery – providing the supply for the noise reduction process.

What effectiveness do the noise cancelling headphones provide?

The majority of models provide the 15-20dB of noise reduction, – that’s almost 70% of external sounds in rather noisy conditions.

Some models can reach the threshold of 30 dB noise reduction. That means if you use them in thoroughfare, or noisy crowded place, e.g. in the city center, almost all the external sounds will be blocked.

On the other hand, extreme noise cancelling values affect sound quality. Noise isolation causes muffling, which makes audio sound a bit unnatural and spaceless. But it’s critical only for musicians and studio work, if you got to use them not for professional purposes – it’s ok.

Besides personal use, noise cancelling headphones are necessary tool in industrial sector. For those who work at the factory, where noise level is really high, this tool is as important as any other tools.