Noise cancelling headphones principle
Noise cancelling headphones methods are two, active noise reduction and passive noise reduction.
Active noise reduction function is through the noise reduction system with the external noise equivalent to the reverse sound waves, the noise and in order to achieve the effect of noise reduction. Active noise canceling headphones with noise suppression with the outside noise of the circuit they use most of the larger headset design, earplugs and Noise cancelling headphones can be used to block the structure of external noise, the first round of noise, but also for the There is sufficient space to install active noise reduction circuit and power supply.
Passive noise canceling headphones mainly through the surrounding ears to form a closed space, or the use of silicone earplugs and other sound insulation materials to block the external noise. As the noise has not been through the noise reduction circuit chip processing, generally only block high frequency noise, low noise noise reduction effect is not obvious.
Noise cancelling headphones were mainly used in the aviation industry, the aircraft engine noise in the human body caused a serious impact, so the national military departments began to develop and use Noise cancelling headphones. With the development of civil aviation, followed by Noise cancelling headphones into the civilian areas. This is why we will find a lot of Noise cancelling headphones box will be printed on the "plane." In the earphone circle, there is a general understanding of when I do not know from the beginning, that is, "Noise cancelling headphones" sound quality is not good.
The noise level of noise cancelling headphones:
1, the earliest noise cancelling headphones is "noise reduction" as the initial purpose, to meet the sound quality can be clear, so the sound quality is not very important;
2, although the noise reduction headphones began to civilian, but the initial research and development purposes have not changed, noise reduction is still the primary goal, so the noise headphones to the people caused the impression of poor sound quality.
Active noise reduction headphones work principle, the more academic argument is that the sound is a kind of pressure wave, composed of compressed part and sparse part, the noise reduction loudspeaker emits the same sound wave with the original acoustic wave amplitude, the opposite wave Interference, superposition of the synthesis of new sound waves, and thus eliminate each other. This is the phase offset.
Modern active control noise headphones are realized by analog circuits or digital signal processing. The appropriate algorithm can analyze the audible and audible noise in the background, and then generate a signal by a specific algorithm, offset from the original signal or vice versa. This phase-reversed acoustic wave is superimposed on the amplitude of the original signal to superimpose, resulting in destructive interference. This effectively reduces the background noise.
Noise cancelling headphones can be placed with noise sources to reduce noise. In this case, the audio power of the noise cancelling headphones must be the same as the noise source. Alternatively, the sensor that emits the noise reduction signal may also be placed in a location where noise is undesirable. This requires a low-power silencer, but it can effectively reduce the noise for a single user. Noise removal is not easy at other locations because the three-dimensional noise wavefront will interfere with the noise reduction signal, and the noise will be reduced in some places, but will be enhanced elsewhere. In a small enclosed environment (such as a small compartment in a train), the overall noise can be measured using multiple loudspeakers, feedback microphones, and dynamic response in confined spaces to achieve noise cancellation.