Ups noise analysis of headphone noise reduction technology

How come you think about this topic? Concerned about the "big player Zhang Lei" public number, his public article mentioned that he took the long-distance flight wearing active noise canceling headphones, can offset the aircraft engine noise, keep the environment quiet, I am very curious, so advanced.

So I found out what is the active noise canceling headphones, just happened, Xiaomi has, but I have not bought. Wait until the next time you have a reason to reward yourself, buy 129, good value for money.

First take the active noise reduction curve of the millet ring iron pro headphones:

What is the first science popular noise reduction:

Active noise reduction is a noise reduction technique and one of the methods used to reduce noise in headphones. The active noise reduction function is to generate a reverse sound wave equal to the external noise through the noise reduction system, and neutralize the noise, thereby achieving 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 principle is the same as the active filter used in the IDC room. Is there a wood? (Those who know the active filter may be less than those who know the active noise canceling headphones...)

Noise reduction effect of headphones = passive noise reduction + active noise reduction

Passive noise reduction, that is, physical noise reduction, for high frequency noise, including acoustic cavity design, earplug material selection and other physical factors; active noise reduction, that is, driven by the power supply, for low and medium frequency, monitoring noise and eventually generating reverse wave cancellation.

Excuse me, there is a bump at the frequency of 7KHz . What is this?

The reason is simple. Our ear canal forms a resonant cavity , which weakens the passive noise reduction capability, ie a bump is formed near the resonant frequency. The sudden drop of the passive noise reduction curve of the millet headphones at around 7 kHz is exactly what it is. Also because this is caused by the self-contained properties of the ear canal, this protrusion is very common and difficult to avoid.

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Is the ear canal resonance frequency around 7KHz?

Wait, what do I seem to think of?

By the way, I used to encounter more than one UPS in the computer room. The noise was loud and loud when I was working. I just pierced my ears and let people want to escape in minutes. . . Yes, it is a model in the high-frequency tower machine. Several major manufacturers have corresponding products, it seems that this feature.

When a unit computer room was relocated, 80KVA 1+1 parallel machine, high-frequency machine, under the copper platoon of the output wiring of two UPS, each mouse died a mouse! !

Have you read something from the eyes above? This little guy is also irritated by high-frequency noise, and he committed suicide, Amitabha. . .

However, it is a mouse, the ear canal structure should be different from people, is it so clever, the ear canal resonance is around 7KHz? Hey, anyway, the voice, I can't stand it, let me stand for about half an hour away from the front of the UPS, it is estimated that my hearing is damaged. Therefore, power electronics engineers, when designing the switching frequency of power devices, try to stay away from the 7KHz frequency.