How Does The Noise Cancelling Technology Work?



When wearing headphones, we usually want to listen to our audio materials and nothing more than that. Headsets and earphones provide some sort of noise isolation, to some extent, but if you want to isolate outside noises completely, you will have to look for a pair of noise reduction headphones. However, this problem is approached by headphone manufacturers from two possible angles, as there are headsets with active noise cancelling technology and/or passive noise control.

When wearing headphones, we usually want to listen to our audio materials and nothing more than that. Headsets and earphones provide some sort of noise isolation, to some extent, but if you want to isolate outside noises completely, you will have to look for a pair of noise reduction headphones. However, this problem is approached by headphone manufacturers from two possible angles, as there are headsets with active noise cancelling technology and/or passive noise control.

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Active noise control implies the use of paired speakers that emit sound with the same amplitude, but with inverted phases, so as to cancel each other. The wave that results in the process called interference is double the initial signal, but has no noise. As headphones are much smaller than regular speakers, active noise reduction is achieved differently in their case. A feedback microphone is used for picking up ambient noise within range of your ears. An inverted sound is then emitted in order to cancel the noise.

Noise-cancelling headphones do have some inconveniences, though.  First of all, they might cause nausea, vertigo and headaches, as a result of making you motion sick. When the sound waves cancel each other, the remaining very low frequency vibrations start stimulating the balance receptors from the inner ear. While it sounds very serious, it seldom happens, and you should worry about this aspect only if you have a very sensitive inner ear. Secondly, active noise control requires power from a battery and when this runs out, the headphones either work as a regular pair, or stop functioning altogether. Besides lower frequency vibrations, noise reduction headphones may also produce high-frequency hiss that along with the noise-cancelling circuitry may deteriorate the sound quality.  On top of the added bulkiness, noise cancelling headsets also cost more than their regular counterparts, so you should take this aspect into consideration, too. Of course, respected audio equipment manufacturers implement new technologies in their products all the time, in order to cut down as many of these drawbacks as possible.

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Passive noise cancellation is achieved by attenuating the noise that gets into your ear. In-ear monitors, as well as circumaural and supra aural headphones provide the best results, while open-back and earbud headphones isolate ambient noise only partially. Closed headphones are able to block 8 to 12 dB, while in-ear monitors close out 10 to 15 dB, depending on the model. If the surrounding environment is not very loud, headphones with passive noise control are probably a better option than the ones featuring active noise cancellation.

Moreover, if you want to make sure that people can't hear what you are listening to, you should opt for headphones with a closed design. Mind you, there are slight differences between open and closed headphones, so you should check both designs before making a purchase.

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The physics principle behind acoustic noise cancelling headphones might be applied in other fields, too. As explained by researchers on Nature Photonics, the speed and reliability of Internet connection could become much better if the signal transmitted via optic fiber is inverted and then added to the original signal, so as to cancel any interference. This technology could open the way for a lot of innovations, even outside the world of audio equipment.