Understanding Piano Action: How a Key Becomes Sound

The Genius of the Grand Piano Action

When you press a key on a grand piano, you set in motion a chain of precisely engineered levers, springs, and felt-covered hammers — a mechanism that must respond to the subtlest variation in touch and return to position in fractions of a second, ready to repeat. This system, known as the repetition action, was developed in the early 19th century and remains the basis of every modern grand piano action.

The Components: A Brief Glossary

The key — the visible lever — connects to the wippen, which transmits the force to the hammer butt and jack. The hammer shank carries the hammer head, covered in dense felt, which strikes the string. The damper — a felt block resting on the string — lifts as the key is depressed, allowing the string to vibrate, and falls back when the key is released, silencing the sound. The escapement mechanism allows the hammer to fall away from the string after striking it, preventing the hammer from damping the vibration it has just produced.

Why Regulation Matters

Over time, the felt components of a piano action wear and compress, and the wooden parts swell and contract with changes in humidity. This affects how consistently and evenly the action responds to touch. A well-regulated action feels the same across all 88 keys; a poorly regulated one has keys that feel heavy, light, or inconsistent. Regular regulation — typically every three to five years — restores the action to its designed specification.

Touch and Tone: The Pianist's Control

The relationship between touch and tone in a piano is more nuanced than most non-pianists appreciate. The speed at which the key is depressed controls the hammer velocity, which controls volume. The speed at which the key is released controls the duration of the sustain. A pianist with refined touch can produce an almost limitless variety of articulations, colours, and dynamics — all through variations in the pressure and speed applied to 88 keys.