The contrabassoon, also called a double bassoon, is the largest instrument in the woodwind family. It produces the lowest sound in the orchestra, with a booming quality in its lowest register resembling that produced with organ pedals. Physically it is very similar to a conventional bassoon, including use of the same materials, and it is played in a similar manner and operates on similar principles. However, it differs with regard to tube diameter and length, reed size, some details of fingering, and the addition of a flared bell.
Because the tube is about twice as long as that of a conventional bassoon, it is curved around on itself instead of being straight. This results in a range solely in the low registers, and the lowest note that can be played is the same as the lowest "A" on the piano keyboard. Thus the main role of the double bass is to support other bass instruments in the orchestra, such as the bass trombone and tuba.
Although the contrabassoon was initially developed around the end of the 17th century, it was not widely used because of intonation problems, including pitch irregularities and the fact that the lowest note was only a fifth below the lowest note of conventional bassoons. These limitations were eventually overcome and the first modern versions were built around the end of the 19th century.