Noise-cancelling headphones

Active noise reduction headphones means active noise control are different from passive sound insulation for general headphones. 

The principle is:

1. Firstly, the signal microphone placed in the earphone detects the low frequency noise (100~1000Hz) 

in the environment that the ear can hear (currently it can reach 3000Hz)

2. Pass the noise signal to the control circuit, and the control circuit performs real-time operations.

3. Acoustic noise is emitted by a Hi-Fi speaker with sound waves of opposite phase and amplitude

4. So the noise disappears and we can’t hear it.

Active noise cancellation headphones are expensive, but generally have excellent results and are comfortable to wear. 

However, independent battery power is required, 

and most passive noise canceling headphones can be used without power consumption (and no active noise reduction)