The word "tannoy" refers to a type of public address system or loudspeaker used for making announcements or playing music in public spaces like airports, train stations, or stadiums. Full definition
All lounges have flight information screens as well as tannoy announcements, so you'll be kept up to date. (holidayextras.co.uk)
For my own system I have used two Tannoy speakers and a NAD amplifier, essentially a high quality stereo system, rather than computer speakers. (treehugger.com)
Typical of this would be the occasion that evangelist Chad Dedmon saw a woman healed in Walmart which so excited the cashier it led to the surprising announcement over the store tannoy — «God is healing people in aisle 3!» (premierchristianity.com)