headphone vs listenership

headphone

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

listenership

noun
  • The act of paying attention to a conversation or speech; listening. 

  • The audience that listens to a certain form or genre of audio material (specifically (Internet, radio), an audio broadcast such as a radio program or a podcast). 

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