Action (piano)

The piano action mechanism, or the key action mechanism, or simply the action of a piano or other musical keyboards, 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 "weighted keys" feeling; that is, the feeling of the heaviness of the touch of the keys."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."

The piano action was the key new addition that Bartolomeo Cristofori created when he invented the piano in 1700. Other than in the action, the first pianos were quite similar in construction to contemporary harpsichords. With the piano, a hammer strikes the string, whereas with a harpsichord, a mechanism plucks the string. Cristofori's action already 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.

After Cristofori's death in 1731, a number of piano makers (for instance, Gottfried Silbermann) built pianos with actions that were essentially copies of Cristofori's. Others produced quite different actions, often simpler and less effective ones. In the 1770s, the Augsburg builder Johann Andreas Stein developed an entirely new action in which the orientation of the hammer was reversed, with the hammer head closer to the player. This "Viennese" action was widely used by makers in Vienna, and was the action of pianos played by Haydn, Mozart, and Beethoven. It survived in Viennese pianos almost to the end of the 19th century.

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