Active noise reduction is a kind of noise reduction technology, which is to generate a reverse sound wave equal to the external noise through the noise reduction system, neutralize the noise, and achieve the effect of noise reduction. Its principle is that all sounds are composed of a certain spectrum. If a sound can be found, its spectrum is exactly the same as the noise to be eliminated, but the phase is just the opposite and the noise can be completely cancelled out.
The sound is generated by the vibration of the object, and the form of the vibration in the elastic medium is the sound wave. The sound wave in a certain frequency range (20 to 20000 Hz) acts on the human ear to produce a sound. Noise is usually defined as "unwanted sound" and is an environmental phenomenon. People are exposed to noisy environments throughout their lives, and noise is also an environmental pollutant produced by human activities. Vibrating (vibraTIon) is a reciprocating periodic motion of an object (or a part of an object) along a straight line or curve and passing through an equilibrium position. It is widely found in nature and engineering.
Since vibration is the source of noise, in the practice of vibration reduction and noise reduction, the noise problem can be effectively solved by solving the vibration. In common noise control, the vibration of thin metal plates, such as the wall of aerodynamic machinery, the outer casing of the machine, the body of the car and the hull are generally made of thin metal plates. When the equipment is in operation, these thin plates will vibrate and radiate noise. Noise such as that caused by vibration of a metal plate structure is called structural noise. For the effective control method of radiated noise of the metal plate, one is to reduce the noise radiation area of ​​the metal plate as much as possible, and to remove the unnecessary metal plate surface; the second is to apply a layer of damping paint on the metal structure, and use the damping material to suppress Structural vibration, noise reduction, this method, we call vibration damping (vibraTIon damping), is an active noise reduction technology.
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. However, it is worth noting that this noise reduction method can effectively isolate high-frequency noise from the outside, but the blocking effect of low-frequency noise is not obvious. In order to actively eliminate low frequency noise, the technology of "active noise reduction" was invented. Its principle is: all sounds are composed of a certain spectrum. If a sound can be found, the spectrum is exactly the same as the noise to be eliminated, but the phase is just the opposite (180° difference), which can completely cancel the noise. . The key is how to get the sound that cancels the noise. The actual approach is to start with the noise source itself and try to reverse the phase of the original noise through the electronic circuit. From this point of view, the technology of active noise reduction is actually "to attack with poison."
Active noise reduction
1. Excessive noise reduction effect may cause the user to hear dangerous warnings and bring danger.
2, due to active noise reduction, battery power is required, but the battery power will be used up. And basically all the noise canceling headphones will not work properly after the battery is used up.
3, active noise reduction solves the problem of low frequency noise, but it is not good to get high frequency noise, noise emitted by vocals, airplanes or trains, active noise canceling headphones are difficult to fully cope.
4. If the active noise reduction equipment is not good, it may cause loss of sound quality.
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