There are two methods of noise reduction in headphones, active noise reduction and passive noise reduction.
The active noise reduction function is to generate anti-phase sound waves equal to the external noise through the noise reduction system to neutralize the noise, so as to achieve the effect of noise reduction. Active noise-cancelling headphones have a noise-cancelling circuit that counteracts external noise. Most of them use a larger head-mounted design, which can block external noise by using earplugs and earphone shells to block external noise for the first round of sound insulation. There is ample space to install the active noise cancellation circuit and power supply.
Passive noise-cancelling headphones mainly block external noise by surrounding the ears to form a closed space, or using sound insulation materials such as silicone earplugs. Since the noise is not processed by the noise reduction circuit chip, generally only high frequency noise can be blocked, and the noise reduction effect on low frequency noise is not obvious.
The three noise reduction measures commonly used to reduce noise, namely noise reduction at the sound source, noise reduction during propagation, and noise reduction at the human ear, are passive. In order to actively eliminate noise, the technology of "active noise cancellation" was invented. Its principle is: all the sounds heard are sound waves, which have a certain spectral composition. If you can find a sound wave whose spectrum is equal to the amplitude of the noise to be eliminated, and the phase is just opposite (180° out of phase), the superposition of the two can completely cancel the noise. The key is how to get that noise-cancelling sound. The actual approach is to start with the noise itself, monitor the noise with a microphone, and then try to generate a reverse sound wave through the electronic circuit and play it out through the speaker. From this point of view, the technology of active noise reduction is actually "fighting poison with poison".
When dealing with complex noise environments, the two MEMS microphones of "active noise reduction" will pick up in-ear noise and various external environmental noises, respectively, and are equipped with an independent intelligent high-definition noise reduction processor to perform high-speed operations on the different noises picked up. Precise noise cancellation. And for the noise reduction needs of different scenarios, the headset provides a variety of listening modes: strong and weak active noise reduction modes and an ambient sound mode. It isolates external noise to varying degrees and eliminates the "black hole feeling" when listening to common noise-cancelling headphones.
