audience vs headphone

audience

noun
  • A group of people within hearing; specifically, a large gathering of people listening to or watching a performance, speech, etc. 

  • The readership of a book or other written publication. 

  • A following. 

  • An audiencia (judicial court of the Spanish empire), or the territory administered by it. 

  • A widespread or nationwide viewing or listening public, as of a TV or radio network or program. 

  • A formal meeting with a state or religious dignitary. 

headphone

noun
  • A cushioned speaker placed on, over, or inside the ear, normally used in left/right pairs. 

How often have the words audience and headphone occurred in a corpus of books? (source: Google Ngram Viewer )