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Physics of Noise-Cancelling Headphones

During the holiday season, many people are frantically travelling across the country to visit friends and family. That means long lines, big crowds and delays—stress abounds. Whether traveling by plane, bus or train, background noise can prevent any relaxing moments. So many travelers turn to noise-cancelling headphones when travelling, and there's some interesting physics behind these high-tech devices.

Noise-cancelling headphones can be broken down into two main groups: passive and active. Passive headphones simply reduce background noise by using insulating materials to prevent external noise from entering the ear. Active headphones, on the other hand, are a little more complex.

Many active headphones have an external microphone that screens incoming sounds. When the microphone detects unwanted noise—such as a humming airplane engine—it sends a sound wave into the headphone speakers that is 180 degrees out of phase with the bothersome sound. Consequently, the two waves cancel each other out, resulting in silence. Unlike traditional earbuds or headphones, noise-cancelers require a rechargeable battery to send out the mirror waves.

So if you're looking for a gift for the music lover in your life, noise-cancelling headphones might be just the thing. Not only do they cancel out background noise, but they also have better sound quality than most earbuds. To learn more about noise-cancelling headphones, you can check out this informational page from Bose or this article from HowStuffWorks.

Headphone image courtesy Gamer112 via Wikipedia.


  1. Noise cancelling headphones are only those that actively cancel the noise by the method you describe.

    "Passive headphones simply reduce background noise by using insulating materials to prevent external noise from entering the ear" are called isolating headphones. They are not noise cancelling.

    "... the two waves cancel each other out, resulting in silence" is perhaps a little optimistic: the process of inverting the sound takes time which is why they become less effective at high frequencies.

  2. Do you have any other suggestions in terms of reputable brands for noise cancelling headphones?


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