Basic trombone anatomy
- tuning slide
- slide lock ring
- water key/spit valve
- main slide
- second slide brace/stay
- first slide brace/stay
- bell lock nut
A disassembled trombone. From left to right: mouthpiece, outer slide, bell section, inner slide.
A tenor trombone mouthpiece
The trombone is a predominantly cylindrical tube bent into an elongated "S" shape. Rather than being completely cylindrical from end to end, the tube is a complex series of tapers with the smallest at the mouthpiece receiver and the largest just before the bell flare. The design of these tapers affects the intonation of the instrument. As with other brass instruments, sound is produced by blowing air through pursed lips producing a vibration that creates a standing wave in the instrument.
The detachable cup-shaped mouthpiece is similar to that of the baritone horn and closely related to that of the trumpet. It has the venturi: a small constriction of the air column that adds resistance greatly affecting the tone of the instrument, and is inserted into the mouthpiece receiver in the slide section. The slide section consists of a leadpipe, the inner and outer slide tubes, and the bracing, or stays. Modern stays are soldered, while sackbuts (medieval precursors to trombones) were made with loose, unsoldered stays (this remained the pattern for German trombones until the mid-20th century).
The 'slide', the most distinctive feature of the trombone (cf. valve trombone), allows the player to extend the length of the air column, lowering the pitch. To prevent friction from slowing the action of the slide, additional sleeves were developed during the Renaissance, and these stockings were soldered onto the ends of the inner slide tubes. Nowadays, the stockings are incorporated into the manufacturing process of the inner slide tubes and represent a fractional widening of the tube to accommodate the necessary method of alleviating friction. This part of the slide must be lubricated frequently. Additional tubing connects the slide to the bell of the instrument through a neckpipe, and bell or back bow (U-bend). The joint connecting the slide and bell sections is furnished with a ferrule to secure the connection of the two parts of the instrument, though older models from the early 20th century and before were usually equipped with friction joints and no ancillary mechanism to tighten the joint.
The adjustment of intonation is most often accomplished with a tuning slide that is a short slide between the neckpipe and the bell incorporating the bell bow (U-bend); this device was designed by the French maker François Riedlocker during the early 19th century and applied to French and British designs and later in the century to German and American models, though German trombones were built without tuning slides well into the 20th century. However, trombonists, unlike other instrumentalists, are not subject to the intonation issues resulting from valved or keyed instruments, since they can adjust intonation "on the fly" by subtly altering slide positions when necessary. For example, second position "A" is not in exactly the same place on the slide as second position "E". Many types of trombone also include one or more rotary valves used to increase the length of the instrument (and therefore lower its pitch) by directing the air flow through additional tubing. This allows the instrument to reach notes that are otherwise not possible without the valve as well as play other notes in alternate positions.
Like the trumpet, the trombone is considered a cylindrical bore instrument since it has extensive sections of tubing, principally in the slide section, that are of unchanging diameter. Tenor trombones typically have a bore of 0.450 inches (11.4 mm) (small bore) to 0.547 inches (13.9 mm) (large or orchestral bore) after the leadpipe and through the slide. The bore expands through the backbore to the bell, which is typically between 7 and 8 1⁄2 inches (18 and 22 cm). A number of common variations on trombone construction are noted below.