blowhorn vs public address system

blowhorn

noun
  • A device, often funnel-shaped and sometimes hand-held, which is used to emit loud sounds or amplified human speech. 

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. 

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