loudhailer /ˌlaʊdˈheɪlə/ (also loud-hailer)

• 1. 

  N-COUNT A loudhailer is a device for making your voice sound louder in the open air. 扩音器 [英国英语]

  例：

  A loudhailer blared warnings of a bomb scare.

  扩音器大声播报炸弹恐吓的警告。