mouthpiece vs public address system

mouthpiece

noun
  • The part of a telephone that is held close to the mouth. 

  • The part of a wind instrument that is held in or against the mouth. 

  • A lawyer for the defense. 

  • A spokesman; one who speaks on behalf of someone else. 

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