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.
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