Acoustic (#; 277), a. [F. acoustique, Gr. &unr_; relating to hearing, fr. &unr_; to hear.] Pertaining to the sense of hearing, the organs of hearing, or the science of sounds; auditory.
[1913 Webster]

Acoustic duct, the auditory duct, or external passage of the ear. -- Acoustic telegraph, a telegraph making audible signals; a telephone. -- Acoustic vessels, brazen tubes or vessels, shaped like a bell, used in ancient theaters to propel the voices of the actors, so as to render them audible to a great distance.
[1913 Webster]