The modern bass trombone is pitched in B♭. It is identical in length to the tenor trombone, but has a wider bore and a larger bell to aid in the production of a fuller, deeper tone in the lower register. It also has one or two valves which, when engaged, change the key of the instrument, allowing the player to bridge the gap between the first partial with the slide in first position and the second partial with the slide fully extended in seventh position. These valves may be configured in a dependent or independent system. In a dependent system, the first valve lowers the key of the trombone to F. The second valve can only be engaged in conjunction with the first valve, and commonly lowers the key of the trombone to E. With an independent system, the first valve still lowers the key to F, but the second valve commonly lowers the key to G♭ when engaged alone or D when engaged with the first valve. 19th and early 20th century examples of the modern bass trombone were sometimes made with a valve attachment in E rather than F, or with an alternative tuning slide for the attachment tubing enabling the pitch to be lowered to E♭. Bore sizes of the bass trombone are generally larger than those of large bore tenor trombones. Typical specifications include a bore size of 0.562″ in the slide and 0.580″ through the valve attachment tubing, with a bell from 9″ to 10.5″ in diameter. Bass trombones with just one valve often have a long tuning slide which allows the valve to change key to E rather than the usual F.
The range of the modern bass trombone is fully chromatic from the lowest fundamental with the valve attachment tubing deployed, potentially as low as C1 (or even the B flat a tone lower), up to C5 or higher, depending on the player. It is usually scored in the range F1 to B♭4.
There is usually one bass trombone in a standard symphony orchestra performing works in the Romantic period or later. It is also seen in military bands, brass bands, jazz bands, wind ensembles, and a variety of brass groups; the bass trombone is usually played by the third trombonist in a symphony orchestra trombone section, the first two parts usually being played by tenor trombones.
Bass trombones in G, F, E♭
Older, now obsolete versions of the bass trombone were of smaller bore than the modern bass trombones described above. They were usually pitched in G, F, or E♭, and had a longer slide with a handle attached to the outer slide stay to allow for full extension of the slide. They were mainly used in Europe and the British Empire.
The oldest of these instruments were the E, D and C bass trombones, which were used in Europe during the Renaissance and early Baroque periods; by the 18th century the F and E♭ bass trombones were used in Germany, Austria and Sweden and the E♭ bass trombone in France, though these fell out of favour in the early nineteenth century and began to be replaced by the tenor trombone, later (after 1840) the tenorbass trombone with F rotary valve attachment.
The bass trombone in G (the orchestral version was in G equipped with a rotary valve attachment actuating D or C, extending the range to A2 or A♭1) enjoyed a period of extended popularity in France during the second half of the nineteenth century, and in Great Britain and the British Empire from approximately 1850 to the 1950s, though it lingered on in some parts of Britain until the 1970s and 1980s and is still occasionally to be seen there in brass bands and period instrument orchestras.
The range of the E♭ bass trombone is A1 to B♭4, that of the F bass trombone is B1 to C5 and that of the G bass trombone is D♭2, or A1 or A♭1 with a D or C valve attachment (the C attachment being used expressly for playing parts written for the contrabass trombone), to D5.