The sound that the human ear can hear is 20-20000hz, while 20-4000 is a normal sound wave, which will not cause harm to people. You've listened to the sound all your life without any side effects. This is also a sound wave.

20-2000 Hz sound, what side effects will it have? And it was developed according to Huangdi Neijing. It has been listed for 7.8 years, and I haven't heard of any side effects! In fact, people say that it goes in one ear and out the other, and you and your relatives need to experience it! ! ! ! ! ! ! ! ! ! ! ! !