The action of an instrument plucked by hand is the distance between the fingerboard and the string. In keyboard instruments, the action is the mechanism that translates the motion of the keys into the creation of sound (by plucking or striking the strings).
1 Keyboard instruments 2 Instruments plucked by hand
2.1 Adjusting the action
In a harpsichord, the main part of the action is a jack, a vertical
strip of wood seated on the far end of the key. At the top of the jack
is mounted a hinged tongue bearing a plectrum. When the key is pressed
and the jack rises, the plectrum plucks the string. When the key is
released and the jack falls back down, the tongue permits the plectrum
to retract slightly, so that it can return to its rest position
without getting stuck or plucking the string again on the way down.
The jack also bears a damper, whose purpose is to stop the vibration
of the string when the key is released. For full description and
diagrams, see Harpsichord.
In a piano, the action is a mechanical device, made mostly of
hardwoods, that serves several purposes. By means of various levers,
it permits a small motion of the key to be translated into a large
motion of the hammers that strike the strings. The action also permits
a hammer to recoil from the string instantly so as not to damp its
vibration, and it also prevents the hammer from bouncing up and down,
striking the string multiple times.
Ibanez RG 770 guitar action
In the guitar and similar instruments, the action is the distance
between the fingerboard and the string, which determines how easy it
is to sound notes when pressure is applied with the fingertips.
Generally a low action is considered to be more playable, due to the
lower amount of pressure needed to press the string to the
fingerboard. However, if the action is set too low, there is a danger
that the vibrating string will strike the frets or fingerboard below
it, creating an unwanted buzzing noise (on fretted instruments, this
is known as fret buzz). Conversely, if the action is too high, then
the strings may be too taut to fully depress.
Adjusting the action
On some instruments, such as certain guitars, the action can be
adjusted by tightening screws at the bridge, which changes the height
of the strings.