hammered dulcimer vs yangqin

hammered dulcimer

noun
  • A type of dulcimer whose metal strings are stretched over a trapezoidal sounding board that has two bridges, one bass and one treble, set on a stand and played with small mallet-like hammers. 

yangqin

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

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