Question

acous·tic
 /əˈkuːstık/ ( also US   acous·ti·cal) /əˈkuːstıkəl/  adj  
  1 : of or relating to sound or to the sense of hearing
   the acoustic properties/characteristics of a room
   acoustic vibrations
  2 a of a musical instrument : not having its sound changed by electrical devices
   an acoustic guitar
   acoustic instruments
  2 b : made with or using acoustic instruments
   She loves listening to acoustic folk music.
   an acoustic performance of a rock-and-roll song
   acoustic musicians
  acous·ti·cal·ly /əˈkuːstıkli/  adv  
   an acoustically perfect room