How Pianos Work

Charmaine Li  /  Articles / Sep 14

How does a piano work? It seems simple: press a key, the key moves a hammer, and the hammer hits a string, the sound of which gets amplified by a wooden soundboard.

But behind this process is a marvelously intricate and exceeding complex machine. Pianos are ingenious instruments designed by ingenious craftspeople before the Industrial Revolution. In this article, we’ll explore what makes a piano, a piano.

  1. A Brief History of the Piano
  2. Piano Action
  3. Strings
  4. Frame and Soundboard
  5. Pedals
  6. How Digital Pianos (Keyboards) Work

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A Brief History of the Piano

Main article: A Complete History of the Piano

Left to right: hammered dulcimer, clavichord, harpsichord

The modern piano we know today came about in the late 1800s. But people have been playing piano-like instruments for centuries.

The pianos’ earliest ancestor is the hammered dulcimer. It’s a box-shaped string instrument played with handheld hammers; in other words, a very simple version of the piano’s mechanism.

Two instruments that came about in the Renaissance and Baroque periods were the clavichord and harpsichord. The clavichord is a small, quiet instrument meant for homes. Unlike the harpsichord, it can play some dynamics. Harpsichords often have two keyboards; one keyboard will have a slightly fuller sound and the other a softer sound.

The fortepiano was a game-changer that arrived around 1700. Invented by Bartolomeo Cristofori, it had the innovative capability to play nuanced dynamics based on a pianist’s touch.

Today, the standard modern acoustic piano has 88 keys. In recent years, there have been significant technological improvements in digital pianos, and today, you can buy a digital piano that closely resembles an acoustic grand at a fraction of the price.

A 1775 fortepiano made by Johann Andreas Stein, creator of the Stein action. (Photo: Gérard Janot, CC BY 3.0)
🎹 FUN FACT: Harpsichord strings are plucked, not hammered. Their “hammers” have a little plectrum, similar to a guitar pick.

How Does a Piano Work? Piano Action

One of the most important parts of a piano is its action. Piano action refers to the mechanism behind pressing down a key and making a sound. This is a very complex mechanism with a lot of moving parts.

Diagram of the action mechanism behind a single key. Source: Olek Ramesz & Bechstein (CC BY-SA 3.0)

Here’s a simplified explanation: the piano key is a lever. By pressing on it, the key activates parts called the wippen, the jack, and the hammer shank. At the same time, pressing the key lifts the damper off the string, so that when the hammer strikes the string, it resonates.


Escapement was a major innovation in the development of the piano. When the hammer shank moves up, there is a point when the jack “escapes” the hammer knuckle. This allows the hammer to hit the string from inertia alone. The hammer can then fall back from the string due to gravity and let it resonate. Without escapement, the hammer would stay on the string and muffle it.

🎹 FUN FACT: Grand piano action feels different from upright piano action because in grand pianos, the hammers return to rest by means of gravity. In upright pianos, hammers return to rest thanks to springs. Gravity makes key repetition more efficient in grand pianos.

Double escapement was first implemented by French piano maker Sébastien Érard in the 1800s. Double escapement allows for faster repetition of a single key because it resets the action without releasing the entire mechanism.

It’s easier to understand this if you watch it in action, so check out the video after this paragraph.

🎹 FURTHER READING: Special thanks to The Piano Deconstructed for explaining the action mechanism in exquisite detail. Check out that website if you want to nerd out further on piano construction!


The piano is, in some ways, both a percussion instrument and a string instrument. There are 88 keys on a piano, but more than 200 strings!

Why so many strings? The higher notes have more strings, and these strings are thinner. Meanwhile, as we move lower down the keyboard, we get fewer strings, and these strings are thicker. Low strings are wound with copper.

In general, the longer and thicker a string is, the lower its pitch. Higher strings require duplicates and triplicates because they’re not as resonant, so they require an extra boost!

With so many strings, pianos hold a lot of tension. In fact, piano strings combine to produce 35,000 pounds of tension! So, how do pianos keep their shape without totally imploding? Answer: a cast iron frame.

🎹 FUN FACT: The shortest strings at the treble end of the piano don’t even have dampers! They’re really not that resonant, so dampers aren’t even needed to dissipate the sound.

Frame and Soundboard

Today, piano frames are made of cast iron. But there was a time, before metalworking was advanced enough, when they were made of wood. Cast iron was a major improvement that allowed for higher string tension and, consequently, more resonance.

On the end of the frame closest to the keyboard is the pin block. This is an area that supports the tuning pins, which are turned by a tuner to adjust the piano’s pitch.

The soundboard is what amplifies the sound created by hammers striking on the strings. The larger the soundboard, the louder the piano. You can imagine the soundboard as a speaker; this means that for large pianos (grands and high-end uprights alike), you’re essentially playing a wall-sized speaker!

Soundboards are used in many instruments, such as in guitars and violins, where the body of the instrument acts like a soundboard. Sitka spruce is the preferred type of wood used for soundboards.

A fascinating documentary on the Sitka spruce soundboards used in Steinway’s pianos.

You can technically use a soundboard made of metal, and this would yield a louder sound. However, metal has a habit of amplifying everything, including the tinny and undesirable high overtones that sound when a metal string is struck. Wood is superior because it amplifies lower frequencies in the bass but suppresses higher frequencies.

🎹 FUN FACT: The holes in the piano’s cast iron frame are called the web. They allow more sound from the soundboard to resonate through. Yamaha has a neat side-by-side comparison of what happens when you block these holes with cardboard.


Many people have questions about piano pedals. And it’s a tad confusing because grands and uprights have different pedalling systems.

  1. In a grand piano, the three pedals are the una corda, the sostenuto, and the sustain pedal.
  2. In an upright piano, the three pedals are the una corda, the practice pedal, and the sustain pedal.

Una Corda

The una corda (“one string” pedal) is sometimes called the “soft pedal.” In a grand piano, pressing the una corda shifts the keyboard to the right. This causes the hammers to hit only two out of three piano strings, creating a slightly softer sound.

In an upright piano, the una corda pedal causes the hammers to shift closer to the keys.

This pedal is used in many late Romantic pieces such as the so-called “impressionist” pieces by Debussy and Ravel.

🎹 FUN FACT: The Una Corda piano by Klavins is a unique designer piano that only has one string per note.

Sustain Pedal

This is everyone’s favorite pedal! It instantly makes everything sound better by creating that dreamy, reverb effect we’ve come to associate with composers like Chopin. But pianists need to be cautious not to overuse it.

Pressing down the sustain pedal causes a rod to lift up all the dampers, allowing any string you hit to resonate even after you let go of the key. Letting go of the sustain pedal reapplies the dampers.

How to use the pedal to sound instantly better. Link to lesson.

Sostenuto Pedal

The sostenuto pedal is similar to the sustain pedal. It also sustains notes—but only select notes.

When you press a key and then press the sostenuto pedal, a rod inside the piano will raise and catch on to a piece of felt. This keeps that key’s damper off the string until the sostenuto pedal is let go.

A demonstration of the mechanics behind all the pedals.

Practice Pedal 

Available in upright pianos, the practice pedal causes a sheet of felt or wool to fall between the hammers and the strings, dampening the sound. This way, you can practice late at night without your neighbors complaining!

🎹 FUN FACT: Modern pianos have around 10,000 moving parts and each key has about 100 parts in its action mechanism. That’s a lot of parts!

How Digital Pianos (Keyboards) Work

Acoustic pianos are fascinating, but more people are choosing to learn on digital pianos.

There was a time when these instruments were unanimously considered inferior to acoustics. But in recent years, technology has progressed significantly. Today, you can get a very high quality digital piano that closely resembles the real thing for a fraction of the price.

The inside of a digital piano is very different from an acoustic’s!

Digital pianos work like computers in that there is an input and an output. The input, in this case, is your finger pressing a key; and the output is sound that comes out of the speaker. Sensors pick up the information you input by playing, and some high-end keyboards can pick up on 1000 touch velocies.

🎹 FUN FACT: Vintage electric pianos (e-pianos) like the Wurlitzer work differently from modern digital pianos. In the Wurlitzer, pressing a key causes a hammer to hit a reed instead of a string. A pick-up then converts the reed’s vibration into an electrical signal that is then amplified through a speaker.

Sampling vs. Modeling

The tone generator of a digital piano is what produces its sound. The two main ways digital pianos generate sound is by sampling and modeling.

Sampling is when engineers record sound from an acoustic piano and then play those sounds when a key is pressed. The idea is simple (you’re essentially pressing a “play” button for a pitch every time you press a key), but technicians take great pains to acquire hundreds of recordings. Waveforms are then mapped and samples can also be modified to account for more realistic dynamics and tone.

Modeling is when sound is synthesized by computers on the spot. While technology for modeling has been around for some time, it wasn’t until recently that sufficient computing power made it possible for synthesis to happen instantaneously.

🎹 FURTHER READING: Merriam Pianos makes very detailed reviews on digital pianos, so make sure to check them out if you’re in the market for one. Recently, they also experimented with seeing whether a piano expert can hear the difference between sampling and modeling.

We hope you now have an answer to the question, “How does a piano work?” If you’re new to piano and in the market to buying one, make sure to read our piano buying guide.

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Charmaine Li is a Vancouver writer who has played piano for over 20 years. She holds an Associate diploma (ARCT) from the Royal Conservatory of Music and loves writing about the ways in which music—and music learning—affects the human experience. Charmaine manages The Note.

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