public address system vs spokesman

public address system

noun
  • An electronic voice-amplification apparatus, usually containing a set of two loudspeakers and a central control unit, used for singing, giving a speech, play-by-play commentary at events, or broadcasting in public areas like in airports or stations. 

spokesman

noun
  • One who speaks as the voice of another person or a group of people. 

How often have the words public address system and spokesman occurred in a corpus of books? (source: Google Ngram Viewer )