megaphone vs public address system

megaphone

noun
  • A portable, usually hand-held, funnel-shaped device that is used to amplify a person’s natural voice toward a targeted direction. 

  • Mouthpiece or promoter; one who speaks for or publicizes on behalf of another. 

  • A cytotoxic neolignan obtained from the laurel Aniba megaphylla. 

verb
  • To use a megaphone; to speak through a megaphone. 

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 megaphone and public address system occurred in a corpus of books? (source: Google Ngram Viewer )