The trumpet has a long remoter ancestry. The modern trumpet, a standard member of the brass section of the orchestra, differs from its predecessors in its use of three valves, by which the length of the tube can be changed to produce the notes of the harmonic series from different fundamentals. Baroque trumpeters came to specialise in the use of the upper or clarino register of the valveless natural trumpet, a register in which adjacent notes were possible. Experiments during the 18th century led to the short-lived keyed trumpet, which could play adjacent notes in the lower register as well. This was used by Haydn in his 1796 Trumpet Concerto. The valve trumpet came into relatively common use in the second quarter of the 19th century. Trumpets are built in various keys, although the B flat and C trumpets are now most often found.