Old English heran (Anglian), (ge)hieran, hyran (West Saxon) "to hear, perceive by the ear, listen (to), obey, follow; accede to, grant; judge," from Proto-Germanic *hausejanan (source also of Old Norse heyra, Old Frisian hera, hora, Dutch horen, German hören, Gothic hausjan "to hear"), from PIE root *kous- "to hear" (source also of Greek koein "to mark, perceive, hear;" see acoustic). The shift from *-s- to -r- is a regular feature in some Germanic languages. For the vowels, see head (n.).
Spelling distinction between hear and here developed 1200-1550. Meaning "be told, learn by report" is from early 14c. Old English also had the excellent adjective hiersum "ready to hear, obedient," literally "hear-some" with suffix from handsome, etc. Hear, hear! (1680s) originally was imperative, an exclamation to call attention to a speaker's words ("hear him!"); now a general cheer of approval. To not hear of "have nothing to do with" is from 1754.
In reference to material meant to deaden sound, 1924. Of sound reproduced mechanically (rather than electrically) from 1932 in reference to gramophone players; acoustic guitar (as opposed to electric) attested by 1958. Related: Acoustical; acoustically.