phonology vs public address system

phonology

noun
  • The way sounds function within a given language; a phonological system. 

  • The study of the way sounds function in languages, including phonemes, syllable structure, stress, accent, intonation, and which sounds are distinctive units within a language. 

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