Answer to Question #49204 in Physics for Trevor

Question

Describe how noise cancelling headphones work.

Answer 1

Answer
When listening to two tuning forks at thesame frequency, you hear enhancement and cancellation of the tones. The
cancellation of the tones is how the noise cancelling headphones work. They
cannot cancel all the noise because of the complexity of the sounds but they
can handle some of it. They start by sampling the outside noise and matching it
in volume and inverting the phase of it producing a canceling effect. This
works great if it were just one sine wave at one frequency. The real word
sounds are complex. The headphones use a computerized sampling of the noise to
produce a complex reversed phase-matched volume noise to block the outside
noise. Examples of this are the Cadillac car exhaust system which samples the
noise exiting the muffler and adds a reverse phase noise to cancel the noise.
At a constant RPM and load, this can bevery effective. During accelerating or decelerating and load changes, the system
is not very effective.