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Those things about noise-canceling headphones! Shallow analysis of noise reduction headset technology

2021-03-27 29
Noise-canceling headphones, what are noise-canceling headphones? Undoubtedly, the literal interpretation is headphones that can reduce noise, and noise reduction headphones can be divided into "active noise reduction" and "passive noise reduction" headphones. Noise-canceling earphones can eliminate environmental noise, provide a quiet and peaceful listening environment for earphone users, and can avoid the behavior of having to increase the music volume due to the interference of environmental noise, which protects the hearing of human ears to a certain extent.

 Passive noise reduction:
 
Before talking about active noise reduction, let's talk about passive noise reduction first. Passive noise reduction is a general term for using a combination of plastic, foam, woven mesh and other composite materials to achieve purely physical noise reduction methods, such as the US military headsets we often see on TV, or those used by airport ground crews The headphones with oversized earmuffs are basically passive noise-cancelling headphones.

Passive noise reduction headphones mainly rely on good airtightness and material characteristics to keep noise out, but passive noise reduction generally can only target higher frequency sounds above 500Hz, especially for noises above 1KHz, which are mostly closed Earphones will show a certain degree of passive noise reduction ability, but to obtain better noise reduction effects and to deal with low-frequency noise, it is necessary to pay a great price (the research of materials science is a big project!)

Since passive noise reduction is incapable of many low-frequency noises, this has led to the development of active noise reduction.

Do you need noise-canceling headphones?

If you are a business person, or a friend who often takes airplanes, I believe that you should have a personal experience of airplane noise. The reason why airplane noise is so tired is greatly related to being in a noise environment for a long time. The roar of the engine In addition to causing damage to human hearing, sound will also have a great impact on the entire physiological environment of humans, which will lead to psychological and mental boredom and fatigue. If this is the case for a long time, it will be tired, easy to get tired, and affect Work efficiency, long-term will cause insomnia, tinnitus, dreams, fatigue, memory decline and other symptoms. Therefore, at this time, if there is the emergence of active noise reduction headphones, these situations can be avoided.

Why have noise-canceling headphones been tepid?

As mentioned above, since active noise-cancelling headphones have such great benefits, why have noise-cancelling headphones been so tepid in the market for so many years?

In fact, since the active noise-canceling headphones were designed for civilian use by professionals, they have always been a niche market. First of all, there are not so many people who need to fly for a long time. Although active noise-canceling headphones have entered the general consumer market in recent years, But its main publicity is still tied to the aircraft, and the distance from the general consumer is still relatively large.

However, in recent years, there has been a good trend that in some headset products, the noise reduction function has become standard. For example, brands such as UE, BEATS, and Magic Voice have popularized the noise reduction function in headsets, although these brands It is not the main noise reduction effect, and there is a gap between the noise reduction level of several established headset manufacturers, but maybe this is the beginning of noise reduction technology really starting to enter the homes of ordinary people.


Those things about noise-canceling headphones! Shallow analysis of noise reduction headset technology


Classification of Active Noise Cancelling Headphones

1. Feedforward active noise reduction: expose the microphone to noise and isolate it from the speaker

2. Feedback active noise reduction: Place the microphone as close to the speaker as possible

3. Combination of feedforward and feedback: There are two microphones at the same time, one is isolated from the speaker, and the other is close to the speaker

Active noise reduction working mode:

1. The microphone collects noise signals

2. The function G(w) performs arithmetic processing on the signal, and parallels the signal to the music signal (the designer is required to perform acoustic analysis on the possible noise and noise, according to the frequency, phase and amplitude of the noise that may be transmitted to the ear Change, establish the function G(w))

3. The horn emits music with noisy reverse sound waves (neutralizes external noise while playing music).

1. Feed-forward active noise reduction design: As shown in the figure, the feed-forward design isolates the microphone from the earphone speaker unit (that is, the sound collection point of the microphone is designed on the surface of the earphone cavity) to ensure that the speaker produces The effect of sound waves on the microphone is small. This design is the most direct method of noise collection. After the microphone collects the noise signal, it is processed by the transfer function G(w), and the reverse sound wave is emitted through the horn to neutralize the noise.

2. Feedback type active noise reduction design: As shown in the figure, the feedback type active noise reduction design the noise collection microphone near the speaker. Compared with the feedforward type, the noise collected by the feedback type is closer to that of the human ear. Hearing noise, but a major disadvantage of this design is that the microphone cannot distinguish the difference between the sound emitted by the speaker and the noise. If there is a sound similar to the noise in the music, it will also be recognized as noise and be processed. This has caused the distortion of music to a certain extent. How to avoid this phenomenon is where the design strength of each manufacturer is reflected.

3. Combination of feedforward and feedback: As shown in the figure, this method combines the above two noise reduction designs with two microphones. In addition to increasing the material cost, this design is for the establishment of the function G(w) It is also a big challenge, but there are already many such noise-canceling headset products on the market.

Summary: Although the author's introduction above is relatively concise, the noise reduction technology is really not that simple. Want to make a truly practical noise reduction headset product is a headache for many manufacturers, and this is why One of the reasons why the noise-cancelling headset products you can see on the market are generally more expensive (small sales are also one of the reasons).

Headphone disassembly view noise reduction technology application

In order to give everyone a more intuitive experience, the author found some visible active noise reduction headset products on the market, did a brief disassembly of them, and classified them according to the noise reduction method.
So even simple disassembly is not available, but there is no microphone hole on the outside of the headset, so it can be regarded as a feedback type active noise reduction design.

In addition, in the field of noise reduction headphones, the author has not obtained the actual noise reduction headphones. It can be found from the network pictures that it has a feedforward microphone. As a well-known noise reduction headset product, I guess it should also be feedforward and feedback. Combined noise reduction design.

Through disassembly, it can be found that there are no earphone products that use feedforward active noise reduction technology. This may indicate that the practical value of pure feedforward noise reduction technology is low. As for pure feedback and feedforward and The feedback-combined noise reduction is better or worse. I don’t know. Although the combined method may seem high-quality, its real practical value and whether it can surpass the feedback-based noise reduction at the level of noise reduction. For professional measurement.
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