When you are walking on the street, taking a subway or having a dinner in a restaurant, you can always see young people wearing different kinds of earphones. Some people hook earphones over their ears; other people insert earphones into their ears; and still others people put earphones over their head. This phenomenon shows that music has become more and more popular among young people. However, they know the music that they like maybe a noise for others. Meanwhile, they have no right to force others to listen to the same music with them. Hence, earphones have become essential equipment for them when listening to the music in the public.