public address system: a set of electrical equipment that makessoundslouder, used especially for making announcements to a group of people or for playing music in a public place 公共广播系统;播音系统
a speaker (=a piece of equipment that sound comes out of) that is designed for high sounds. A speaker designed for low sounds is called a woofer. 高频扬声器
a speaker (=a piece of equipment that sound comes out of) that is designed for low sounds. A speaker designed for high sounds is called a tweeter. 低音扬声器;低音喇叭