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您的位置: 首页 ->  常见问题 PROBLEN -> 汽车主动降噪系统会不会造成安全隐患?
  目前业界较好的车内主动降噪系统,其最高工作频率也只能达到200到240赫兹左右(某些系统的主动降噪频率可以达到700甚至1000Hz),上面提到的环境噪音几乎都不在这个范围。一般的交谈声波频率都在200赫兹以上,警车及喇叭就更高了。这要从主动降噪的原理说起。简单点说,主动降噪原理是通过测量进入接受者耳部的环境噪音的波型,通过计算,使用有源声源在接受者耳部产生一个幅度相同但相位相反的声波,从而使合成声波的振幅降低,达到降噪的目的。这是理想的情况,在现实中几乎不可能实现,因为以上每个环节(测量,计算,广播)都会产生误差。比如说,以汽车为例,如何准确的测量进入驾驶者耳部的噪音波形?目前的解决办法是将麦克风置于顶棚或头枕中。置于头枕还好一点,如果置于顶棚,控制系统如何知道麦克风距驾驶者耳部的距离(头枕也一样)?准确距离不知道,那麦克风测量的噪音如何能反映驾驶者索听到的真实噪音?计算环节,首先要分析声波频率,然后产生同幅度反相位的声波,如何在极短的时间内实现?考虑到目前计算机速度及成本,系统计算速度在短时间内很难提高。广播环节,如何让目标地(耳部)准确的接收产生所产生的波形?同样需要有源声源到目标地的距离。
  何况车内空间大,有源声源不止一个,相互之间有干扰。综上,目前车内主动降噪只能降低低频噪音,因为
  1. 低频噪音的波长较长, 200赫兹的声波波长大概为1.7米,测量及广播环节的距离误差所带来的影响较小;
  2.可以承受一定时间的计算迟滞;
  3. 成本不会高到离谱。车内主动降噪的幅度也有限,在其工作频率范围内的降噪效果大概在3到10分贝。但是也有某些频率得到少量加强的情况。那车内的低频噪音有哪些?主要是部分发动机噪音,路噪及部分风燥。为什么降噪耳机能够更好的消除噪音?
  因为1.降噪耳机的麦克就放在耳机外侧,可以更准确的测量进入耳朵的噪音,广播时也不用考虑距离的问题,使其工作频率可以更高一些。
  2.耳机有很好的被动降噪,即将你的耳朵包住,高频噪音也得到部分的消除。即便没有主动降噪,某些大耳机的被动降噪效果都可以达到13到15分贝。这里提到的所有分贝都是A加权分贝。

At present, the industry-leading in-vehicle active noise reduction system, the maximum operating frequency can only reach about 200 to 240 Hz (the active noise reduction frequency of some systems can reach 700 or even 1000Hz), the above mentioned environmental noise is almost not in this range. The average conversational sound frequency is more than 200 hertz, police cars and horns are even higher. This should be based on the principle of active noise reduction. Simply put, the principle of active noise reduction is to measure the type of ambient noise that enters the receiver's ear. Through calculation, an active sound source is used to generate a sound wave with the same amplitude but opposite phase in the receiver's ear, so that the synthetic sound wave The amplitude is reduced to achieve noise reduction. This is an ideal situation, which is almost impossible to achieve in reality because each of the above steps (measurement, calculation, broadcast) will produce errors. For example, taking a car as an example, how can we accurately measure the noise waveform entering the driver's ear? The current solution is to place the microphone in the ceiling or headrest. Better placed on the headrest, if placed on the ceiling, how does the control system know how far the microphone is from the driver's ear (like a headrest)? The exact distance does not know, how can the noise measured by the microphone reflect the actual noise heard by the driver? In the calculation section, we must first analyze the frequency of sound waves, and then generate sound waves of the same amplitude and opposite phases. How can we achieve this in a very short time? Taking into account the current computer speed and cost, the system speed is difficult to improve in a short time. In the broadcast session, how can the target place (ear) accurately receive the generated waveform? It also requires the distance from the active source to the target.
Moreover, there is a large space in the car, and there are more than one active sources, and there is interference between them. In summary, active noise reduction in the car can only reduce low-frequency noise because
1. The low-frequency noise has a long wavelength. The 200 Hz wavelength of the sound wave is approximately 1.7 meters. The influence of distance error in measurement and broadcast links is small.
2. It can withstand a certain amount of computing hysteresis;
3. The cost will not be so high. The amount of active noise reduction in the car is also limited, and the noise reduction effect in the operating frequency range is about 3 to 10 dB. However, there are also cases where some frequencies are slightly strengthened. What are the low frequency noises in that car? Mainly engine noise, road noise and some wind dryness. Why noise canceling headphones can better eliminate noise?
Because 1. The microphone of the noise reduction earphone is placed on the outside of the earphone, can measure the noise that enters the ear more accurately, do not need to consider the problem of the distance while broadcasting, make its working frequency can be higher.
2. The headset has a very good passive noise reduction, that is, wrap your ears, high-frequency noise has also been partially eliminated. Even without active noise reduction, some large headphones can achieve a passive noise reduction of 13 to 15 dB. All the decibels mentioned here are A-weighted decibels.
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