A Dictionary of Music and Musicians/Double Flat

DOUBLE FLAT. If the flat lowers a note by a semitone, the double flat lowers it by two. The sign for the double sharp is abbreviated, but that for the double flat remains simply ♭♭, the corrective to which is either ♮♭ or ♭ at pleasure. On keyed instruments the double flat of a note is a whole tone lower:—thus A♭♭ = G♮, C♭♭ = B♭. The French term is double bémol; the German one doppel-B. The German nomenclature for the notes is Eses, Asas, Deses, etc.