The trumpet is constructed of brass tubing bent into a rough spiral. The trumpet and trombone share a roughly cylindrical bore which results in a bright, loud sound. The bore is actually a complex series of tapers, smaller at the mouthpiece receiver and larger just before the flare of the bell begins; careful design of these tapers is critical to the intonation of the instrument. By comparison, the cornet and flugelhorn have conical bores and produce a more mellow tone.
As with all brass instruments, sound is produced by blowing air through closed lips, producing a "buzzing" sound into the mouthpiece and starting a standing wave vibration in the air column inside the trumpet. The player can select the pitch from a range of overtones or harmonics by changing the lip aperture and tension (known as the embouchure). Modern trumpets also have three piston valves, each of which increases the length of tubing when engaged, thereby lowering the pitch. The first valve lowers the instrument's pitch by a whole step (2 semitones), the second valve by a half step (1 semitone), and the third valve by one-and-a-half steps (3 semitones). When a fourth valve is present, as with some piccolo trumpets, it lowers the pitch a perfect fourth (5 semitones). Used singly and in combination these valves make the instrument fully chromatic, i.e., able to play all twelve pitches of Western music. The sound is projected outward by the bell.
The trumpet's harmonic series is closely matched to the musical scale, but there are some notes in the series which are a compromise and thus slightly off key; these are known as wolf tones. Some trumpets have a slide mechanism built in to compensate for this.
The mouthpiece has a circular rim which provides a comfortable environment for the lips' vibration. Directly behind the rim is the cup, which channels the air into a much smaller opening (the backbore or shank) which tapers out slightly to match the diameter of the trumpet's lead pipe. The dimensions of these parts of the mouthpiece affect the timbre or quality of sound, the ease of playability, and player comfort. Generally, the wider and deeper the cup, the darker the sound and timbre.
