bass viol vs double bass

bass viol

noun
  • A fretted, bowed, stringed musical instrument from the viola da gamba family. It occupies the bass range and is the lowest instrument in the family. Similar to (but smaller than) a cello. 

double bass

noun
  • The largest stringed instrument of the violin family. 

  • The deepest of all male voices. 

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