Public broadcasting can not only play background music and sound reinforcement, the system includes background music and emergency broadcasting functions, usually combined together. It is targeted at public places, in corridors, elevator doors, Combined sound columns or dispersed speaker boxes are installed in elevator cars, lobbies, shopping malls, restaurants, bars, banquet halls, community gardens, etc. to play background music at ordinary times. When an emergency occurs, it is forced to be used as an emergency broadcast. Use it to direct the evacuation of the crowd.