Timpani

The timpani (informally called the "kettledrums") describes a low-pitched set of large drums, which since the middle of the 17th-century have formed the backbone of the orchestra's percussion section.

Early versions of the timpani appeared in pairs, and since they were cumbersome to tune, the tuning was set before the performance on fixed pitches which matched the key of the work being performed. Most usually this equated to the tonic and dominant degrees of the scale. Modern timpani on the other hand, can be tuned very easily using a foot pedal, and usually exist in the modern orchestra as a set of five.