crwth vs double bass

crwth

noun
  • An archaic stringed instrument associated particularly with Wales, though once played widely in Europe, and characterized by a vaulted back and enough space for the player to stop each of the six strings on the fingerboard. Played variously by plucking or bowing. 

double bass

noun
  • The largest stringed instrument of the violin family. 

  • The deepest of all male voices. 

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