Bass Trombone

The modern bass trombone is pitched in B-flat.
Its tubing length of 9 feet (2.7 m) is identical to
that of the tenor trombone, but it has a wider
bore, a larger bell, and a larger mouthpiece.
Bass trombones also have one or two valves
which can change the key of the instrument.
This allows the player to bridge the gap
between the first partial with the slide in the
first position and the second partial with the
slide fully extended in the seventh position.