Well ... to be fair, Acoustic originally just means you can hear it.

acoustic
1605, from Fr. acoustique, from Gk. akoustikos "pertaining to hearing," from akoustos "heard, audible," from akouein "to hear," from copulative prefix a- + koein "to mark, perceive, hear," from PIE base *(s)keu- "to notice, observe" (see caveat). Acoustics is attested from 1683. Acoustic guitars (as opposed to electric) first attested 1966.
Dictionary of Etymology