Adjective
Referring to a sound that has no visually identifiable cause.
Referring to Pythagorean disciples who for years listened to his lectures from behind a curtain, unable to see him.
(music) Referring to pre-recorded music that is presented in concert using loudspeakers, e.g. some types of computer music.
Source: en.wiktionary.org"What the GRM Brought to Music: From Musique Concrète to Acousmatic Music". Source: Internet