As a composer, Spohr produced more than 150 works with opus numbers, in addition to a number of nearly 140 works without such numbers. He wrote music in all genres. His nine symphonies (a tenth was completed, but withdrawn: Cf.) show a progress from the classical style of his predecessors to program music: his sixth symphony represents successive styles from "Bach–Handel" to the moderns; his seventh symphony represents the 'sacred and secular in human life' with a double orchestra; and his ninth symphony represents "Die Jahreszeiten" (The Seasons). (The autograph score of the tenth symphony, which bears the complete work, is held by the Staatsbibliothek Berlin. Furthermore the same institution holds a complete set of copied parts. Cf. also ). Between 1803 and 1844 Spohr wrote more violin concertos than any other composer of the time, eighteen in all, including works left unpublished at his death. Some of them are formally unconventional, such as the one-movement Concerto No. 8, which is in the style of an operatic aria, and which is still periodically revived (Jascha Heifetz championed it), most recently in a 2006 recording by Hilary Hahn. There are two double-violin concertos as well. Better known today, however, are the four clarinet concertos, all written for the virtuoso Johann Simon Hermstedt, which have established a secure place in clarinettists' repertoire.