Principle of noise reduction earphones
There are two noise reduction methods for earphones: active noise reduction and passive noise reduction.
The active noise reduction function is to neutralize the noise by generating a reverse sound wave equal to the external noise through the noise reduction system, so as to achieve the effect of noise reduction. Active noise reduction earphones are equipped with noise reduction circuits that can compete with external noise. Most of them adopt a large headworn design, which can block external noise by using earplug cotton and earphone shell and other structures for the first round of sound insulation. At the same time, active noise reduction circuits and power supplies are installed in order to have sufficient space.
Passive noise reduction earphones mainly form a closed space by surrounding the ears, or use sound insulation materials such as silicone earplugs to block external noise. Because the noise is not processed by the noise reduction circuit chip, it can only block high-frequency noise, and the effect of noise reduction for 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 in the process of transmission and noise reduction at the human ear, are passive. In order to actively eliminate noise, people invented the technology of "active noise elimination".
Its principle is that all sounds heard are sound waves, which have a certain spectrum composition. If a sound wave can be found, its frequency spectrum is equal to the noise amplitude to be eliminated, and its phase is just opposite (difference is 180 °), the noise can be completely eliminated by superposition of the two. The key is how to get the noise canceling sound.
Starting from the noise itself, use a microphone to monitor the noise, and then try to generate a reverse sound wave through the electronic circuit and play it out through the loudspeaker.
