Double Bassoon
the deepest-toned instrument of the bassoon family; also called contra-fagotto. It stands in the same relation to a bassoon as the doublebass does to the violoncello; that is to say, its sounds are actually an octave below those indicated. Its compass is from B flat below CCC to tenor F. The great masters have written for it largely.
Haydn gives it an important part in several of his works, as do also Spohr, Beethoven, and Mendelssohn.