santoor vs yangqin

santoor

noun
  • An Indian string instrument, a trapezoidal hammered dulcimer with seventy strings, believed to be derived from the Persian santur. 

yangqin

noun
  • A Chinese musical instrument, a hammered dulcimer traditionally fitted with bronze strings. 

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