Noise-cancelling headphones, using active noise control, are different from passive noise isolation of general headphones. The principle is:
1. First, detect low-frequency noise (100 ~ 1000Hz) in the environment that can be heard by the ear using the signal microphone installed in the earphone.
2. The noise signal is then sent to the control circuit, and the control circuit performs real-time operations.
3. Play a sound wave with the opposite phase and the same amplitude as the noise through the Hi-Fi speakers to cancel the noise.
4. After superimposing, the noise disappears and cannot be heard.
