earphones vs headphones

earphones

noun
  • A pair of small loudspeakers worn inside each outer ear or covering all or part of the ear, without a connecting band worn over head. 

headphones

noun
  • A pair of cushioned speakers worn over or in the ears so only the wearer can hear the sound. 

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