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How noise-cancelling technology works for headphones

  

Bose pioneered the concept of noise-cancelling headphones way back in 1989 after more than 10 years of research. ET explains how this fascinating technology works.

Noise cancellation in the car

You may have experienced that some cars are quieter than others - this is because of the special attention paid to insulating materials (special laminated glass for example).

However, there's only so much that passive noise isolation can accomplish inside the complicated acoustics of the car.

That's why luxury carmakers have been implementing active noise cancellation for a quieter cabin. The same active noise cancelling technologies used in headphones can be easily implemented in a car. See image for details.

How it works Simply put, active noise cancellation works by 'listening' to unwanted ambient sounds, and then producing a sound that is exactlyit but with an inverted phase - the two sounds then cancel each other out.

Refer to the diagram for a more detailed explanation. Sound travels in waves, with crests and troughs. Active noise cancellation uses microphones that monitor the sound comingoutside - the internal circuitry then creates a sound that is exactly opposite and pipes it into the speaker drivers along with the music.

No noise cancellation headphones can claim to completely eliminateunwanted sounds - but a good pair can significantly reduce ambient sounds by as much as 80%.

Limitations

Active noise cancelling tech is usually better at blocking out lower frequency sounds. Higher pitched sounds will usually be let through, so active noise cancelling headphones usually employ sound isolation as well.

Noise cancelling headphones/earphones can block out unwanted sounds, but they can also block out sounds that you should be hearing - such as someone calling out to you or traffic headed your way.

That's why you shouldn't wear them and walk around. Or choose somethingBose's QC20 that has an 'aware' mode that lets you hear what's around you while still cancelling out continuous noise.

Pitfalls

Most active noise cancelling headphones give you a 'pressurised' feeling - you'll feel it in your ears - a feeling quite similar to what you feel in an airplane cabin at high altitudes. For some people, the eerie silence is too much to take.

Batteries are required for the tech to work - some headphones stop working altogether if the batteries die out. Plus, since there's a lot of circuitry, there's more that can go wrong.