We know that there are three ways to deal with noise pollution. One is to take noise reduction measures at the sound source, the second is to take noise reduction measures on the transmission route, and the third is to take noise reduction measures at the human ear.
For the third method, the specific measures mainly include the use of
Protective Earmuffs, earplugs and headphones.
The over-ear noise protection earmuffs are made into earmuffs by compounding the sound-absorbing and sealing flexible cushion of the sound-insulating shell to isolate the external noise by surrounding the ears. Since this method is external sound insulation, there is relatively enough space for the design of sound insulation earmuffs to achieve better sound insulation and sealing, and the sound insulation effect is guaranteed. The disadvantage is that it is bulky, not portable, and not suitable for hot weather use.
In-ear sound insulation earplugs are made of sound-absorbing elastic materials to fill the ear canal, so as to achieve the effect of sound insulation. According to the different materials of earplugs, it can be roughly divided into two categories: silicone and polyurethane. Choose the right size earmuffs and earplugs, and when worn correctly, you can achieve a noise reduction effect that significantly blocks external noise. The disadvantage of in-ear earplugs is that due to the penetration into the ear canal, long-term use will cause friction and pain, and the stethoscope effect will occur from time to time.
Whether it is an over-ear earmuff or an in-ear earplug, passive noise reduction technology is used, which reduces noise by blocking and sealing. For medium and high frequency noise, the effect is better, but for medium and low frequency noise, due to its strong penetrability, the effect is relatively poor. The medium and low frequency noise is the most irritating to the human body, which is why the medium and low frequency noise is unacceptable even if the sound is small.
Corresponding to passive noise reduction technology is active noise reduction technology, and active noise reduction headphones are an important application of this technology.
Active noise-cancelling headphones use the built-in electronic noise-cancelling system to achieve better noise-cancelling effects. The electronic noise reduction system is mainly composed of a pickup (mobile phone ambient noise), a processing chip (analyzing noise), a speaker (producing echo sound waves), and a power supply system (providing power). After collecting the ambient noise, it is analyzed by the processing chip, and then the reverse sound wave equal to the external noise is generated to neutralize the noise, so as to achieve the effect of noise reduction. In acoustics, the principle behind this technique is called "destructive interference".
Wearing active noise-cancelling headphones, you will feel that the ambient background sound you hear becomes high-frequency, because the noise-cancelling headphones mainly filter out the middle and low frequency components in the noise. So why is destructive interference mainly aimed at the middle and low frequencies? The reason is that the mid-low frequency waveforms are long and stable, with slow natural decay, while the high-frequency waveforms are relatively short and change rapidly, with fast natural decay. This means that mid- and low-frequency noise can be well picked up by the microphones in the active noise-cancelling headphones and analyzed and calculated in the processing chip. And high-frequency noise may have changed before the active noise-cancelling headphones emit reverse sound waves. The active noise-cancelling headphone market is a mixed bag, with uneven products and large and high price changes, so it is easy to enter the pit. Depending on the quality of the product, there will be different degrees of defects, such as noise floor, wind noise, ear pressure, current pop, etc. In addition, due to the inevitable signal delay and complex changes in the external environment, the noise reduction effect of active noise reduction headphones Nor is it perfect.
In general, all kinds of ear noise protection products and their respective characteristics, in order to exert the best noise reduction effect, still depends on the scene of use. In addition, the price/performance ratio can not be ignored, in short, the most suitable one is the best.
