loud·speak·er 
/ˈlaʊdˌspi:kɚ/ noun
plural loud·speak·ers /ˈlaʊdˌspi:kɚ/ noun [count] : a device that is used to make sound (such as music or a person's voice) louder and to send it out so that many people can hear it in a public space
▪ He made an announcement over/on the loudspeaker. = He made an announcement using the loudspeaker.
▪ He made an announcement over/on the loudspeaker. = He made an announcement using the loudspeaker.
