The bass clarinet in Bb is twice as big as the clarinet in Bb (and therefore sounds an octave lower).
It consists of five parts, as does the clarinet:
- The beak-shaped mouthpiece with a single reed is larger, the reed wider than the Bb clarinet’s;
- A crook (S-shaped piece of tubing) connects the mouthpiece and upper joint. The instrument has no barrel (bulging section of tube) like the clarinet does;
- The keywork is arranged on the upper joint (left-hand joint) and lower joint (right-hand joint);
- The funnel-shaped bell points backward up the tube at an angle of nearly 180 degrees.
A spike is usually attached to the bell so that the instrument can be rested on the floor during playing. If the musician plays standing up, it is held by a strap.
Unlike the higher-pitched clarinets (Bb clarinet, piccolo clarinet), on which some of the tone holes are covered by the fingers (finger-holes), all the tone holes on the bass clarinet are covered by keys. This is due partly to the enormous length of the tubing, which means that the tone holes are too far apart to be reached by the fingers and some cannot be reached by the fingers at all, and partly because they are too big to be covered completely by the fingertips. However, the body is large enough to accommodate the additional keywork.
The bass clarinet has two speaker keys (D5 and E5), whereas the clarinet has only one speaker key and uses the Bb key for overblowing as well. Depending on the model, the bass clarinet’s second speaker key is either fully automatic (linked to the first speaker key and other keys) or mechanical. However, the fully automatic version requires a more complicated mechanism and is less reliable, so many clarinetists prefer the mechanical alternative, on which the two speaker keys can be opened by two separate touch-pieces.