Look at your ears Age
have a test:
7000 Hz-Prove that you are not deaf, because anyone can hear this frequency.
13000 Hz-Indicates that your ears are younger than 50 years old.
14000 Hz-Indicates that your ears are younger than 40 years old.
15000 Hz-Indicates that your ears are younger than 30 years.
16000 Hz-indicating that your ears are younger than 25 years.
...
If you can insist on hearing 20,000 Hz sound, then congratulations, you are definitely the best choice.
0-30000 Hz, choose a frequency arbitrarily, come with your friends younger than anyone else's ear!
Come and try it out!