Traité des objets musicaux (Pierre Schaeffer)
Not exactly a sound design book, but very interesting approach to sound objects and their relationships. The book explains different types of listenings and proposes a classification of sounds by type and morphology.
This theory derives from german phenomenology and it's the founding text of Musique Concrète in France.
I don't know if there are translations in english. I have read the spanish version, a translation of the original work of Schaeffer in frech.
Very recommended reading!