public-address system; PA system
A device or set of equipment used to amplify sound so that announcements or speech can be heard over a wide area.
The morning assembly announcements were broadcast over the school's PA system.
The train delay was announced over the station's public-address system.
スピーカー refers to a single loudspeaker unit, while 拡声装置 is the whole amplification and announcement system.
マイク is a microphone, which is often a component of a 拡声装置.
Compound of 拡声 (かくせい, 'sound amplification') and 装置 (そうち, 'device, equipment').