classical guitar vs nylon-string guitar

classical guitar

noun
  • A type of flat-tabled guitar of Spanish origin used primarily for Western classical music, flamenco, and Latin American music, with six nylon (formerly gut) strings, usually played with the fingers rather than with a plectrum. 

nylon-string guitar

noun
  • A guitar strung with nylon strings and with a neck that joins the body at the twelfth rather than the fourteenth fret, as in a typical guitar. 

How often have the words classical guitar and nylon-string guitar occurred in a corpus of books? (source: Google Ngram Viewer )