earmuff vs headphone

earmuff

noun
  • A sound-deadening cup or a pair of such cups worn over the ear or ears. 

  • A garment to keep the ears warm. 

  • A garment or part worn over a single ear. 

headphone

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

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