What is the principle of noise-cancelling headphones?

At present, there are mainly two types of noise-cancelling headphones, one is active noise-cancelling headphones, and the other is passive noise-cancelling headphones, which are completely different in terms of noise reduction principle and noise reduction effect.

passive noise reduction

Passive noise reduction is also called physical noise reduction. Its principle is very simple and rude. It isolates the ear from the external noise through the physical properties of the noise reduction material. The principle is simple and the cost is low, and the noise reduction effect for high-frequency sound is obvious. To put it bluntly, you plug your ears with your fingers, which is also considered passive noise reduction. Like in-ear headphones and over-ear headphones, these are passive noise reduction effects achieved through earplugs and earmuffs.

Active Noise Cancellation

Active noise reduction actually uses the principle that sound waves can cancel each other out. Therefore, active noise-cancelling headphones will collect external noise signals through the microphone, and then send sound waves opposite to the noise through the headphones in real time, thereby offsetting the noise that falls into the ear. The degree of noise reduction is also determined by the level of the reverse sound wave.