acoustic vs hard rock

acoustic

adj
  • Utilizing sound energy in its operation. 

  • (of building materials) Used for soundproofing or modifying sound. 

  • (of an explosive mine or other weapon) Able to be set off by sound waves. 

  • Naturally producing or produced by an instrument without electrical amplification or the need thereof. 

noun
  • The properties or qualities of a room or building that determine how sound is transmitted in it. 

  • A medicine or other agent to assist hearing. 

hard rock

noun
  • A rock music genre marked by a heavy regular beat, high amplification, and usually frenzied performances. 

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