Physics Form 5: Chapter 1 - Application of Destructive Interference

Noise Cancellation

• Noise cancellation is a method to reduce or completely cancel out undesirable sound.
• A noise-cancellation speaker emits a sound wave with the same amplitude, frequency but anti-phase with the original sound.
• The waves will combine each other in a process called destructive interference, eventually the waves will cancel each other and there would be no sound.
• The sum of the waves is equal to zero.

 

Application of noise cancellation:

1.  Headphone - people working near aircraft or in noisy factories can now wear these electronic noise cancellation headsets to protect their hearing.
2. Cars - The way it works is that a microphone connected to the car stereo system picks up all the sound inside the car, including music or such from the stereo. Then the noise-cancellation system subtracts the sound of the music coming from the stereo and produces noise-canceling sound waves that match the frequency of unwanted sound.
3. Aircraft - The system uses microphones to pick up the vibrations due to jet's engine in the cabin walls. It then analyzes the signals and generates counter vibrations in the walls to produce a net result of zero vibrations.