There are two ways to reduce noise for noise cancelling headphones for office, active noise canceling and passive noise canceling.
The noise canceling system generates a reverse sound wave equal to the external noise, neutralizes the noise, and achieves the effect of noise canceling.
Active noise canceling headphones have a noise canceling circuit that counteracts external noise. Most noise canceling headphones for office use a large head-mounted design. The earplug cotton and headphone shell can be used to block external noise and finish the first round of sound insulation. Besides, in order to have enough space, active noise canceling circuits and power supplies are equipped.
Mainly by surrounding the ears to form a closed space, or using silicone earplugs and other sound insulation materials, it can help block external noise. Since the noise has not been processed by the noise canceling circuit chip, it can generally only block high frequency noise, and the noise canceling effect on low frequency noise is not obvious.
The three noise canceling measures commonly used in noise cancelling headphones for office to reduce noise, namely noise canceling at the sound source, noise canceling during transmission, and noise canceling at the human ear, are all passive.
In order to actively eliminate noise, people invented the "active noise canceling" technology. Its principle is: all sounds are composed of a certain frequency spectrum. If you can find a sound whose frequency spectrum is exactly the same as the noise to be eliminated, but the phase position is exactly opposite (a difference of 180°), the noise can be completely balanced out.
The key is how to get the sound that cancels the noise. The actual method used is to start with the noise source itself and try to reverse the phase position of the original noise through the electronic circuit. From this point of view, the technology of active noise canceling of noise cancelling headphones for office is actually "combating poison with poison."