How a Modern Grand Piano Actually Works

I have sat at a grand piano almost every day of my adult life, and I still find myself pausing to appreciate what is underneath that polished lid. Most of my students never think twice about it. They press a key, a note rings out, and that feels like enough. But once you understand what is actually happening inside that instrument — all the tension and felt and wood and iron working together — you start to hear the piano differently. I think that is worth knowing, whether you are a curious parent, a student who wonders why we talk so much about touch, or someone thinking about starting lessons and wondering what all the fuss is about.

So let me walk you through it, the way I would explain it sitting beside you on the bench.

Three Jobs, One Instrument

The simplest way I know to picture a grand piano is this: three systems doing three different jobs, all at the same time. The action decides when and how a hammer strikes. The strings and cast-iron plate handle the raw vibration. And the soundboard turns that vibration into sound you can actually hear across a room. Pull any one of those three apart and the instrument stops working. Together, they are remarkable.

A standard modern grand has 88 keys. But it does not have 88 strings. In the middle and upper registers, each note is served by two or even three strings tuned in unison, which is why the total string count in a typical grand runs to around 230. Those extra strings add richness and volume. They also mean the piano is under enormous stress. A concert grand carries roughly 18 to 20 tons of total string tension — and some large concert instruments push closer to 30 tons, though that upper figure is model-dependent and varies by maker. Either way, it is a staggering amount of force for a wooden instrument to hold.

The Backbone: That Heavy Iron Plate

The cast-iron plate is what keeps the piano from tearing itself apart. It is the heavy internal frame you see when you look inside, usually painted gold or copper. It does not make a single note of music. Its job is entirely structural: hold the string tension, keep everything stable, and allow the wooden parts around it to do their more delicate work. Without it, the strings would simply pull the whole instrument to pieces over time. With it, a well-maintained grand can hold its tuning reasonably well even through seasonal changes in humidity and temperature.

I mention this to parents because it is part of why a quality piano is worth protecting. The plate is doing quiet, invisible work every hour of every day.

The Soundboard: The Real Loudspeaker

Here is something that surprises most people. The strings themselves do not move much air. A vibrating piano string is thin and fast-moving, but it cannot push enough air on its own to fill a room with sound. What actually does that work is the soundboard — a large, thin panel of wood, typically spruce, that runs beneath the strings. The strings transfer their vibration through a component called the bridge, and the bridge passes it into the soundboard. The soundboard then flexes and moves the air around it, the way a speaker cone does in a stereo. The size and quality of that wooden panel have a great deal to do with the depth and warmth of a piano's voice.

When a technician talks about a piano sounding "alive" or "open," the soundboard is usually part of what they are describing.

The Action: Érard's Brilliant Invention

The mechanism that translates a key press into a hammer strike is called the action, and the version we use in modern grands is known as the double escapement action — sometimes called the double repetition action. It was invented by a French piano maker named Sébastien Érard, who patented it in 1821. I think it is one of the more elegant mechanical solutions in the history of any instrument.

Before Érard's design, a pianist who wanted to repeat a note quickly had to wait for the key to fully return to its resting position before striking again. That limited what was musically possible. Érard's mechanism introduced a small intermediate lever that catches the hammer partway on its return, allowing the key to retrigger before it is fully up. The result is that rapid repeated notes — the kind you hear in fast octave passages or trill figures — become cleanly possible. Every time a student plays a trill and it comes out even, they have Érard to thank, even if they have never heard his name.

I should be honest that secondary sources tell this history with slightly varying details around the later refinements to that mechanism. What is consistent is Érard's invention in the early 1820s as the foundation of the modern grand action. That much is settled.

The Felt on the Hammers

Each hammer in the piano is wrapped in felt, and that felt matters more than most people realize. The density and condition of the felt shapes the color of the note — its brightness, its edge, its roundness. Harder felt tends to produce a brighter, more focused tone. Softer felt sounds rounder and warmer. Piano technicians can actually voice a piano by needling the hammer felt to soften it, or by treating it to firm it up, adjusting the instrument's character without touching the strings at all.

This is one reason I tell students that how you press a key genuinely changes the sound. The speed and weight of your touch affects how the hammer contacts the strings, and the felt mediates all of that. Touch is not a vague musical idea. It has a physical explanation.

I will add a small honest caveat here: the published literature on hammer felt is less precise and standardized than the research on string tension or soundboard physics. What I have described reflects well-established technician practice, but the exact specifications vary by manufacturer and are not as neatly documented as some other aspects of the instrument.

What the Three Pedals Actually Do

Students learn the pedals by feel long before they understand them mechanically, and I think knowing the mechanics helps. Here is what is really happening when you press each one.

• The right pedal — called the damper pedal or sustain pedal — lifts all the dampers off all the strings at once. Normally, a felt damper rests on each string and stops it from vibrating the moment you release a key. Lift them all away, and every string is free to ring. Notes blur together, sympathetic strings vibrate, and the whole instrument opens up. Used well, it is beautiful. Used carelessly, it is muddy.
• The middle pedal — the sostenuto pedal — is the most mechanical of the three. When you press it, it catches and holds only the dampers for notes that are already depressed at that moment. Notes you play afterward are unaffected. This lets a bass note ring on while the right hand plays cleanly above it. It is a specific tool, not an everyday one, but composers have written for it directly.
• The left pedal — the una corda pedal — on a grand piano physically shifts the entire action slightly to one side. Most treble hammers then strike only two of their three strings instead of all three. The result is softer volume and a genuinely different tone color, not just quieter but changed. On an upright, a different mechanism is usually used to approximate the same effect, which is one reason the una corda pedal sounds more distinctive on a grand.

Why Any of This Matters at the Keyboard

I did not write all of this just to satisfy curiosity, though that is a good enough reason on its own. Understanding the instrument changes how a student relates to it. When a young student knows that the soundboard is doing the amplifying, they start to understand why we talk about letting notes breathe. When they know the action is a precision mechanism, they start to take seriously the idea that sloppy finger position produces an uneven tone — because it does, physically. And when a parent understands that 18 to 20 tons of tension is resting on that cast-iron plate, it becomes a little clearer why we protect the piano from extreme heat and humidity, and why tuning twice a year is not optional.

For adults thinking about starting lessons: none of this complexity is something you need to master before you sit down. But knowing that the instrument has this much engineering behind it might actually be encouraging. It means the piano has been refined over two centuries to respond to the human hand as expressively as possible. It is built to meet you where you are.

A Note for Prospective Students

If you have been reading this and wondering whether the Judy Rohlin Piano Studio might be a good fit for your family — or for yourself — I would love to talk with you. Lessons here are for children and adults at all levels, and I am happy to answer questions about instruments, scheduling, or what to expect in those first few months. You can reach the studio through the contact information on this site. There is no pressure, just a conversation. The best way to know if piano lessons are right for you is to ask someone who has spent a career watching people fall in love with the instrument.