Siegfried Wilhelm Dehn was a German music theorist and counterpoint teacher. He made diligent researches on various subjects connected with music both in Germany and Italy, which he utilised in Marx's Berliner Musikzeitung and other periodicals. In 1842, on the recommendation of Meyerbeer, he was appointed librarian of the musical portion of the Royal Library at Berlin, to whose construction and extension he considerably contributed. He was given the title of Königl. Professor in 1849. He catalogued the entire musical library, and added to it a number of valuable works scattered throughout Prussia, especially Pölchau's collection, containing, besides many interesting theoretical and historical works, an invaluable series of original manuscripts of the Bach family.
Siegfried Wilhelm Dehn became an author of music-theoretical works and publisher, and was a sought-after counterpoint and composition teacher. He scored no fewer than 500 motets of Orlando di Lasso, and copied for the press an enormous number of works by J.S. Bach. He was who first published Bach's 6 concertos for various instruments (Peters, 1850); the concertos for 1, 2 and 3 claviers; and the 2 comic cantatas. In 1850 he was a co-founder of the Bachgesellschaft (the Bach Society). He also published a collection of vocal compositions in 4, 5, 6, 8 and 10 parts, called Sammlung älterer Musik aus dem XVI. und XVII. Jahrh. He succeeded Gottfried Weber in the editorship of the musical periodical Caecilia (l842-1848). He had re-edited Marpurg's treatise on Fugue (Leipzig, 1858), had translated Delmotte's work on Orlando di Lasso, under the title Biographische Notiz über Roland de Lattre, and was preparing a larger work on the same subject, from valuable materials collected with great labour, when he died. Among his many distinguished pupils were famous composers as Michail Glinka, Nikolai and Anton Rubinstein, Martin Traugott Wilhelm Blumner, Peter Cornelius, Friedrich Kiel, Carl August Haupt, Albert Becker and Theodor Kullak.
Among Siegfried Wilhelm Dehn's friends were Kiesewetter and Fétis, for the latter of whom he collected materials equal to two volumes of his Biographie universelle. His theoretical works were Theoretische-praktische Harmonielehre (Berlin, 1840; 2nd edition Leipzig, 1858); Analyse dreier Fugen . . . J. S. Bach's. . . und Bononcini's, etc. (Leipzig, 1858), and Lehre vom Kontrapunkt (Schneider, 1859). The latter, published after his death by his pupil Scholz (2nd edition, 1883) contains examples and analyses of canon and fugue by Orlando di Lasso, Marcello, Giovanni Pierluigi da Palestrina, etc. Dehn was a good practical musician and violoncellist.