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Every Mechanism

Home How a Piano Works

Eighty-eight keys, one clever action

How a piano works

Press a key and a felt hammer flies up, strikes the strings and falls away again, all in a few hundredths of a second. Behind every key is a small machine of levers, felts and springs. Here is a grand piano, cut open.

Slow down one key
88
keys, each with its own action
236
strings in this piano
20t
pull of the strings on the frame
2mm
the hammer flies on its own
A black grand piano on a stage in front of a red velvet curtain, sawn open beside G above middle C: the keys in front, the rows of pale wooden action parts on their rails behind them, felt hammers rising to the strings at the cut, the tuning pins in the pinblock, and the long strings stretching back over the gold iron frame.
A grand piano sawn open beside G4, a few keys pressed: their hammers rise to the strings.

Video

How a Piano Works - Inside a Grand Piano

Watch on YouTube

3D model · cut open · play it

Play it, slow it, take it apart

A grand piano sawn open beside G4, so you can see the action behind every key. Play the keys under the model, or click a key on the piano itself, and watch its hammer fly to the strings. Slow it right down, press the pedals, drag to turn the view and scroll to zoom.

Try itPlay a key on the keyboard below. Slow motion lets you watch the hammer fly up, strike the strings and fall back.
Loading the 3D model…

Meet the parts

Ten parts, one grand piano

The piano sawn open beside G4, so every layer shows: the black case; the gold iron plate with the strings stretched over it; the soundboard underneath; the keys, their action and the hammers in front; the dampers resting on the strings; and the pedals below. Tap any part, or pick a name.

A grand piano sawn open beside G4, seen from above its treble side: the keys and the action in front, the rows of hammers and dampers, the gold cast-iron plate with the tuning pins and the strings over it, the soundboard, the black case on its legs, and the three pedals below.

Hover or tap the picture. Amber rings mark every part.

Parts diagram

From the key to the damper

Middle C’s key and action, seen from the side with everything in front of it cut away. The numbers follow the push of your finger: the key, the parts that lift the hammer and let it go, the hammer and its strings, the parts that catch it, and the damper.

Middle C's key and action from the side: the long key on its balance rail with the capstan near its back, the wippen above it carrying the jack and the repetition lever, the let-off button by the jack's toe, the hammer on its flange with the knuckle and the felt head under the string, the backcheck on the key's back end, the damper underlever and the damper resting on the string, and the end of the sostenuto rod, with sixteen numbered parts.

At rest: the hammer lies on its rest rail, the jack stands under the knuckle, and the damper sits on the strings.

    How it works, step by step

    Twenty-one steps from a key to a note

    The same steps as the video. Each picture is a moment from it; press Show me in 3D to set the model up for that step.

      A black grand piano on a stage with its lid open.
      Step 1 of 21

      From a key to a note

        Demo · the heart of it

        The escapement, up close

        Press middle C in slow motion. The jack lifts the hammer, trips on the let-off button and slips away, so the hammer flies the last two millimetres on its own. It bounces off the strings and the backcheck catches it.

        The hammer has to be free when it hits: still pushed against the strings, it would stop them at once. Press very slowly and it never gets there at all. Let the key up only half way and press again: the repetition lever holds the hammer up so the jack can slide back under it, and the note can be played again quickly.

        • Amber: the part pushing the hammer, or holding it.
        • Red: the let-off button, lit when the jack’s toe meets it.
        • Gold rings: the strings sounding. They stop when the damper lands.
        –key pressed down
        –hammer below the strings
        –hammer speed at the strike
        –the hammer is

        Demo · length, weight and pull

        Tune a string

        A string’s note depends on how long it is, how heavy it is and how hard it is pulled. Halve its length and the note goes up an octave; make it heavier and the note goes down; pull it harder and the note goes up. Then bring an out-of-tune string into tune with its two partners, as a tuner does.

        –vibrations a second
        –nearest note
        –off that note
        –its pull on the frame

        Demo · three pedals

        Sustain, soft and sostenuto

        Play the keys and watch the dampers. A key lifts only its own damper; let go and the damper drops and stops the note. Then try each pedal.

        • Right, sustain: lifts every damper, so every note rings on.
        • Left, soft: slides the keys and the action sideways, so each hammer strikes two of its three strings.
        • Middle, sostenuto: a rod turns and holds up only the dampers that are already up. New notes are still stopped by their dampers.
        –notes sounding
        –dampers off the strings
        –strings each hammer strikes
        –held up by the middle pedal

        Demo · why a soundboard?

        A loud note from a thin string

        A string on its own is nearly silent: it is so thin that the air just slips round it. The bridge passes its vibration into the big spruce soundboard, which pushes a broad sheet of air to and fro. Strike the same string with and without the board.

        –how loud it sounds
        –rings until silent, about
        –energy still in the string
        –area pushing the air

        More to know

        Kinds, history and care

        Six kinds of piano

        Strings lying flatGrand pianoThe piano on this page. Its strings run away from you, the hammers strike them from below and fall back by their own weight, and the repetition lever lets a note be played again quickly.
        Strings standing upUpright pianoThe strings and soundboard stand on end to save floor space. The hammers swing forward to strike, and springs bring them back, since gravity cannot.
        The biggestConcert grandAround 2.7 metres long, with the longest bass strings and the biggest soundboard: the piano of concert halls.
        The smallest grandBaby grandAbout 1.5 metres long. The bass strings are shorter, so they are made heavier to sound as low.
        Strings across a boxSquare pianoA rectangular case with the strings running from side to side. It was the home piano of the late 1700s and the 1800s.
        Mozart’s pianoFortepianoThe early piano: a wooden frame, thin strings and small leather-covered hammers, much lighter and quieter than a modern piano.

        From Florence to the concert hall

        1. Bartolomeo Cristofori, in Florence, builds a harpsichord-like instrument whose strings are struck by hammers, so it can play both soft and loud: piano e forte.
        2. The oldest of Cristofori’s pianos that survives today. It is in the Metropolitan Museum of Art in New York.
        3. Mozart writes home praising the pianos of Johann Andreas Stein of Augsburg, whose hammers let go of the strings cleanly.
        4. Sébastien Érard’s double escapement: a repetition lever lets a note be struck again before the key has risen all the way.
        5. Alpheus Babcock of Boston patents a one-piece cast-iron frame, for a square piano.
        6. Steinway & Sons is founded in New York.
        7. Henry Steinway Jr. patents a grand piano with the bass strings crossing over the others.
        8. Albert Steinway patents the sostenuto pedal, the middle pedal.

        Looking after a piano

        • Have it tuned once or twice a year. The strings slowly stretch and the wood moves with the seasons, so the notes drift.
        • Keep the room’s air steady. The soundboard and the pinblock are wood: very dry or very damp air makes them shrink or swell, and the tuning goes.
        • Keep it away from radiators, sunny windows and outside walls.
        • Have the action regulated now and then. Felt and leather wear and compress; a technician resets the let-off, the repetition and the dampers.
        • Clean the keys with a barely damp cloth, never a spray, and close the lid over them to keep the dust off.
        • Keep drinks and plants off it. Water inside can swell the action and rust the strings.

        Things worth knowing

        Piano means “soft”The full name is pianoforte, “soft-loud”, because unlike the harpsichord it could play both.
        From 27.5 to 4,186Most pianos have 88 keys, from A0, which vibrates 27.5 times a second, up to C8, about 4,186.
        A440The A above middle C is tuned to 440 vibrations a second, and every other note is set from it.
        A flight of 2 millimetresThe jack lets go of the hammer only a millimetre or three before it reaches the strings.
        Soft to loudA hammer reaches the strings at under a metre a second when you play very softly, and at several metres a second when you play very loudly.
        Where it is struck mattersHammers strike a string roughly an eighth of the way along it. Overtones that would have to stand still at the strike point are hardly made at all, so the strike point shapes the tone.
        Quick check

        Four questions