How about Steve Reich's 'Music for 18 Musicians'? Depends on what you define as ambient. If we're talking spacey, arhythmic with little dynamic range, then Gustav Holst's 'Neptune: The Mystic'
Would fit the bill. If we're talking Musique Concrete, Stockhausen's 'Gesang der Junglinge'.
― 3×5, Sunday, 17 June 2012 14:37 (eleven years ago) link