the second partial E in seventh, as well as providing alternate slide positions for other notes in long (sixth and seventh) positions. Because the attachment tubing increases the length of the overall instrument by one-third, the distances between slide positions must also be one-third longer when the valve is engaged, resulting in only six positions available on the F slide, to low C. Thus, the F attachment cannot provide the low B♮, but it usually has a sufficiently long tuning slide to lower it into E as required, which will provide B♮ in a very long position. Tenor trombones without a valve are sometimes known as straight trombones. Bass The modern bass trombone usually has two valve attachments to provide all of the notes that are absent on an instrument with no valves (B♮ – E). This allows the player to produce a complete chromatic range upwards from the pedal register. The first valve is an F attachment the same as that found on a tenor trombone and extends the range down to C. The second valve, engaged together with the first, lowers the instrument to D (or less commonly, E♭) and provides the low B. The second valve can be dependent, where it serves to lower the F attachment to D and has no effect alone. More commonly the second valve is independent, where it can be engaged separately to lower the instrument to G♭, or to D when both are engaged. Single-valve B♭ bass trombones with an F attachment are made but are uncommon. They are essentially very large bore tenor trombones, and likewise cannot provide the low B♮ without lowering the valve to E with a long tuning slide. Contrabass Contrabass trombones in F typically have two independent valves, tuned either to C and D♭ combining to A, or in European models tuned to D and B♭ combining to A♭. Contrabass trombones in low B♭ usually have only one valve in F, although Miraphone make a model in C with two independent valves in G and A♭, which combine to E. Valve types The most common type of valve seen for valve attachments is the rotary valve. Many improvements of the rotary valve, as well as entirely new and radically different valve designs, have been invented since the mid 20th century to give the trombone a more open, free sound than the tight bends in conventional rotary