The piano action mechanism (also known as the key action mechanismPressing, Jeffrey Lynn, PhD (1946–2002), (1992) Synthesizer performance and real-time techniques, p. 124. or simply the action) of a piano or other musical keyboard is the mechanical assembly which translates the depression of the keys into rapid motion of a hammer, which creates sound by striking the strings. Action can refer to that of a piano or other musical keyboards, including the electronic or digital stage piano and synthesizer, on which some models have "weighted keys", which simulate the touch and feel of an acoustic piano. The design of the key action mechanism determines the "weight" of the keys, i.e., the force required to sound a note or striking power. "A professional pianist is likely to care most about the piano's action, because that is what controls its responsiveness and relative lightness--or heaviness--of touch. Roughly speaking, a piano's action is light when its keys fall easily under the fingers, and heavy when a noticeable downward thrust is required. The action, in short, is what makes a piano playable or not to an individual musician."
History The string hammer action was the important innovation that Bartolomeo Cristofori created when he invented the pianoforte; Cristofori is credited with building his first instrument by 1700. Pollens, Stewart (1995) The Early Pianoforte, pp. 43-45. Cambridge: Cambridge University Press. Although similar hammer actions were devised at about the same time by Marius (1716) and Christoph Gottlieb Schröter (1717), Cristofori was the only one of these three to actually construct an instrument. Alfred Dolge notes the first pianos were quite similar in construction to contemporary harpsichords, while incorporating key features of the clavichord, including the soundboard, metal strings, and percussive-string method of creating sounds.
With the piano, a hammer strikes the string, whereas with a harpsichord, a mechanism plucks the string. Cristofori's improved escapement action (1720) embodied many of the principles still found in 2000-era actions. It used levers to magnify the small motion of the piano key into a large motion of the hammer, and was arranged so that the very last part of the hammer's motion before striking the string would be purely the result of inertia and not propelled by the key; this prevents the key from pressing the felt-covered hammer firmly into the string, which would damp and stop the string vibrations and the sound.
Horizontal (grand) actions
In Cristofori's improved escapement action (1720), when the key is depressed, the other end of the key-lever raises a horizontal hopper (which Cristofori called the linguetta mobile) with a stepped projection; the hopper raises the curved hammer butt. Because of the stepped projection, the hopper slips off the key just before the hammer strikes the string, providing the escapement action. Other modern features are apparent in his diagram, including the presence of a back check to facilitate repetition, and using the rising tip of the key-lever to lift the damper.
Cristofori died in 1731 and left no significant pupils; the instruments that were in process were finished by Giovanni Ferrini, who also is credited with building a pianoforte dated to 1730. However, Gottfried Silbermann built pianos with both Cristofori and Schröter actions. Silbermann produced Schröter action pianos as early as 1728; Silbermann also built two Cristofori action pianos which were submitted to Johann Sebastian Bach; according to Bach's pupil Johann Friedrich Agricola, Bach rejected them for having a weak treble and heavy action, and Silbermann did not build more Cristofori action pianos for two decades, when he built several for Frederick the Great in 1747.
Two of Silbermann's pupils, Johannes Zumpe and Americus Backers, popularized the Cristofori action as the "English" action after moving to London. Zumpe introduced the square piano between 1760 and 1765; Alfred James Hipkins called Zumpe's action "rudimentary but efficient". The pianos built by Backers did not survive, but his action, patented in 1776, was refined by Robert Stodart (1777) and John Broadwood (1780); the resulting "English" action was noted by Hipkins as "the best single escapement action". Perhaps the best-known English piano action of the nineteenth century is the Brooks action of 1810.
Silbermann also was responsible for popularizing the Schröter or "German" action. Dolge characterizes Schröter's original action as "a model of innocent simplicity ... a clumsy device [that] made the touch hard and tough"; Silbermann improved the escapement of the original design. One of Silbermann's pupils, the Augsburg builder Johann Andreas Stein, further refined Schröter's action in the 1770s by reversing the orientation of the hammer, with the hammer head closer to the player. As described by Hipkins, in the original "Viennese" action, "the blow is caused by the depression of the key raising the hammer-butt until the back of it comes in contact with a rail at the back of the keyboard, the result being to jerk the hammer to the string". Stein also refined this action by adding an escapement. This "Viennese" action continued to be developed by Stein's daughter, Nannette Streicher, and was widely used by other makers in Vienna, and was the action of pianos played by Haydn, Mozart, and Beethoven, as it was characterized by a "pleasant light elastic touch and [a] charming musical quality of tone". It survived in Viennese pianos almost to the end of the 19th century.
In the 19th century, the English action was further modified by French builders, notably in the invention of the repetition lever, which facilitated rapidly repeating notes.Kibby-Johnson, Bill (né William James Kibby; born 1947) (ed.), "Piano Numbers as a Guide to Date" (updated November 2016). Great Yarmouth, Norfolk, England: Piano History Centre (retrieved November 8, 2016, via , website registrant: Bill Kibby-Johnson. Sébastien Érard invented the double-escapement action which incorporated the repetition lever, patented in 1808 and 1821; Dolge credits Érard with combining the refined touch of the Vienna action with the force and power of the English action. The 2000s-era grand piano action is a distant descendant of Cristofori's original.
One of the most well-known French piano actions was created by Jean Schwander in 1844 and improved upon by his son-in-law Josef Herrburger; the Schwander action is still used in Bechstein pianos. At the turn of the century, Schwander-Herrburger merged with Brooks, giving us the Herrburger-Brooks piano action, which was the definitive piano action of the twentieth century. Throughout the history of the action, piano makers tended to make it heavier and sturdier, in response to the increasing size, weight, and robustness of the instrument, which was itself part of a general demand for a more powerful sound.
Vertical (upright) actions
Christian Ernst Friederici invented the first upright piano action in 1745, but it was not well-regarded; Hipkins likened it to a Nuremberg clock. The first upright piano was built by Johann Schmidt in 1780, and improvements were made by various engineers and inventors in the early 1800s, including John Isaac Hawkins, but it was not accepted as a proper musical instrument until 1826, with the introduction of Robert Wornum's upright piano action, which has continued with few changes to the modern upright. Ignaz Pleyel adopted Wornum's action and it is popularly known as the Pleyel action.
Electronic keyboard actions Manufacturers of electronic keyboards, synthesizers, and digital pianos have used various designs to recreate the feel of an acoustic piano. The simplest electronic keyboards, sometimes known as synth-action, use springs to restore each key to its resting position, similar in concept to a computer keyboard, but providing the least realism. More sophisticated keyboards incorporate weights in the keys but rely on springs for return, making these semi-weighted keyboards fast to depress and slower to return.
Keyboards that use moving weights similar to the motion of hammers without relying on springs are called hammer-action. The hammer weights may vary by the note being played, similar to how keys in the bass register of the piano have heavier hammers to sound the thicker strings than those in the treble register; these are known as progressive hammer-action keyboards. Many electronic keyboards use keys that are hinged at the back to minimize keybed depth; some use keys that pivot in the middle or have longer pivot arms with higher-end keybeds, similar to acoustic pianos.
Examples The action primarily serves to mechanically amplify a relatively small (key) movement into a longer, faster (hammer) movement. As an overview, when a key is depressed, a felt hammer strikes one or more strings, causing them to vibrate. The vibrations are transmitted to the soundboard, which makes the audible note. The action also automatically retracts the hammer after it strikes the string(s), preventing it from damping their vibration. In addition, as long as the key is depressed, the action also lifts a felt damper off the appropriate string(s), sustaining the vibration.
The main difference between grand and upright piano actions is the direction of motion. In the grand piano, the soundboard is horizontal; the hammer rises and strikes the string(s) from below, and gravity is used to restore the damper and hammer to their resting positions. In an upright piano, the soundboard is vertical; the hammer strikes the string(s) from the side, and a combination of gravity and springs are used to restore the damper and hammer to their resting positions. The key feel when playing repeated notes is slightly different on these actions, as a result.
Traditionally, the individual parts of the action of an acoustic piano are made of wood with metal pins and pivots; some manufacturers have switched to using plastic and composite materials for certain items to add strength and environmental stability.
Modern grand action
The key (1) is comparable to a seesaw; when the player depresses one end, the end on the other side of the pivot point rises. The capstan (2) is on the rising side of the key. The rising capstan lifts the wippen (3), which is connected to the L-shaped jack (5). The rising wippen carries the long end of the jack, which pushes on a felt knuckle near the pivot point of the hammer shank (8), causing the felt-covered hammer (10) to rise and strike the string(s) (16).
Simultaneously, the rising end of the key also lifts the spoon (14), which is connected to a felt block called the damper (15), which normally rests on the string(s), preventing vibrations. With the damper lifted, the string(s) vibrate after the hammer has struck them.
The short end of the jack is tripped by the letoff button (4) just before the moment the hammer strikes the string(s), causing the long end of the jack to slip off the knuckle; the hammer continues to rise and strike the string(s) by inertia, but then the hammer rebounds and falls back down. In this way, the felt hammer is prevented from dampening the vibrations after striking the string(s), as it would if it remained in contact with the string(s).
If the key remains depressed, the hammer is held above its initial resting position by the back check (11), which is on the same (rising) side of the key as the capstan; this facilitates rapid repetition of notes without fully returning the key to rest, as the repetition lever (9) raises the hammer shank far enough to reset the long end of the jack back under the hammer knuckle for additional key strikes.