What is going on inside a piano?

If you're looking for basic piano facts or information about a specific part of the piano (e.g., hammers, strings, soundboards), you might want to check out the topics I've covered in the series of articles I have written for the Iowa Music Teachers Association magazine.  They are in the second section of the sidebar.

Pianos are complex machines, so any explanation of "what's going on" will be simpler if you already have some background information.  And you might find what you need without going through all the details that follow.

To answer the question briefly, I will divide the piano into three main groups:  the keys, the action, and the strings.  For each major group, I will describe what it does, show you a picture of at least part of it, and then describe what to look for if you are inspecting a piano to add to your family.  The pictures and my descriptions are for a vertical piano, although everything is generally applicable to any piano.

This is only an overview.  If you want more information, there are many great books available.  A list is included on my Books for piano owners page.  The Piano Technicians Guild also offers many resources.

If you don't find the info you want on this website, please drop me a line, if you'd like.  I'll gladly answer your piano question, if I can.


When you press down on the front of a key, the back rises up like a seesaw and sets the action in motion.  The key is actually much longer than what you see from the outside of the piano.  

Each key connects you to a section of the action inside the piano.  Through the action, each key moves a hammer that strikes a string or set of strings to create vibrations.  Depending on how you push and hold the key, you can make the sound louder or softer and longer or shorter.  When you let up on the key, the sound should stop.

In a grand piano and in most vertical pianos, the action sits on the top of the key.  In spinet pianos, the action hangs off the back of the key.   

Push down on one end of
            the key, and the other rises.
Keys must be in good condition and steady on their balance pins in order to work well (like a seesaw).  If you can move them sideways more than a little bit, then the "felt bushings" that keep them steady on their pins are worn away.  This will make it harder to control the piano and can also cause damage to the action, especially the hammers. 

If a key is hard to push down, or if it doesn't come back up (or only part-way), then something is wrong.  A key should go down and up smoothly so you can play smoothly.

Customers often tell me their piano's keys are "sticking", but they often mean very different things by that word. 

Sometimes a key really does stick in the down position. 

If that happens, try this:  push the keys directly beside the stuck key (a half-step up and a half-step down, black or white).  If the stuck key comes back up, then you know something is jammed between
the sticking key and the one that released it. 

If the key stays down no matter what you do, something is broken.   If the key goes up and down smoothly but no sound is produced, something is broken.

If the key plays once or twice but then stops making noise, the action is out of regulation.  If that key stays a little lower than its neighbors, then the key itself needs to be adjusted.

Call your technician if any of these things happen.  Simple mechanical problems can take the joy out of playing, so get them fixed!  (If you're determined to fix them yourself, get a copy of Reblitz before you start poking around - and do NOT use WD40 anywhere inside a piano!)


The action is a large collection of many moving parts that all work together so that the hammer hits the string(s) at the right time.  The relationship of the keys and the action matters because that's how the power gets transmitted from the player's muscles to the hammers and the strings.  The more direct the route, the easier it is to control the piano (and therefore, the sound).  

A grand
              piano's action sits on top of the keys.
So a grand is the most responsive in many ways, since you are almost directly connected to the hammer.  You push the key down, and the hammer goes up.

In this drawing of a spinet action, the key is truncated at the right side of the picture.  But you can see that most of the action is actually below the key! 

The spinet's action
              "hangs" below the keys.
That's why a spinet is the hardest to control: because the power has to make at least four turns before it gets to the string -- 360° just to get from the end of the key to the bottom of the hammer.  And since every turning point is a potential energy-waster, a lot of power and control can be lost in a spinet.

              upright's action is above the keys, too.

Large, mostly older upright pianos have a "sticker" that sits between the key and the action (the piece next to the up arrow in this drawing).  Modern, smaller uprights (e.g. "studio" and "professional" uprights) use a shorter adjustable piece, and console actions sit directly on the key.

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Action parts are made mostly of wood and wool felt, and they are held together with steel pins and glue.  With age and use, the parts can start moving at the wrong time or for the wrong distance.  That's when your piano needs to be regulated, so everything works together to help you play well.  (See the information on
what a technician does for more about that.)
Strings, dampers, and
              hammers work together.
If a piano has lived in a very damp or a very dry place, the wood and felt might have been affected.  A piano is a perfect place to grow mold, if it has been in too much moisture (such as a flood or a damp basement).  

A piano that has gotten too dry will have cracks in various places.  Wood and glue joints can break if a piano is too dry, and other parts can develop serious problems, as well. (More about that in the next section.)  Keys that move but make sound are often a sign of broken action parts.  It might not be a major problem, but again, you want to know about it.

If you remove the front of the piano to look at the action, also check for signs of mice.  Pianos can be both home and restaurant for mice, and they can do a great amount of damage pretty quickly.  Look for shredded paper, stains on the tops of keys, chew marks on the edges of keys, and scat.



The sound of a piano (like all sound) is created by vibration.  When a hammer hits a string, the string vibrates -- and the way that the string vibrates is what makes a piano sound like a piano.  Think about it:  many instruments make sound by vibrating strings, but they all sound different.  You can tell a guitar from a piano from a harp because the patterns of vibration are different.

In general, the longer the strings in a piano, the better the sound will be -- more pure, easier to tune, prettier.  So a grand piano will tend to have the best overall sound.  And when you compare that to a spinet, you can really tell the difference in the sound quality.  (If you want to know more about piano sound, read Reblitz!)  

Once the hammer hits them, strings would keep right on vibrating until they ran out of energy, but all the sound would run together and sound mushy, which isn't what you want.  So, when you let up on the key, a damper touches the strings and stops the vibration for that note.

One, two, or three strings?  The strings that create low sounds are very heavy, long single strings.  The next group of strings is not as heavy or long, so you need two of them to equal the volume of a single heavy string.  The last group of strings, the ones that create high sounds, are much lighter and shorter, so they come in sets of three.  If there weren't three of them, the lower strings would drown them out.

Your piano’s strings produce sound by vibrating, and different speeds of vibration produce different pitches.  Bass strings vibrate more slowly; treble strings vibrate faster.  Because they are tight (and there are so many of them, 240 or more in most pianos), the strings may exert as much as 20 tons of tension on your piano (enough to lift a house from its foundation!). 

Each string wraps around a tuning pin, which can be turned to make the string tighter (higher pitch) or looser (lower pitch).  The tuning pins extend into a pinblock, which is made of at least several layers of plywood.  That block of wood is what holds the pins tight and helps keep the strings at the right tension (so they will produce the pitches you expect).

 Tuning pins in a

Damp or dry conditions can have a major effect on strings and the pin block in a piano.  If a piano is kept in a damp place, the strings might rust.  That will make their sound very "dead" and will increase the chances that they will break during a tuning.  

A piano kept in a place that is too dry will not have rusted strings, but the wood in the pinblock may have shrunk.  Now the tuning pins won't hold against the pressure of the strings, so your piano won't stay in tune.  

There are other wooden parts that can shrink and crack if the piano gets too dry.  One of the most important parts is the "bass bridge".  If you pull the bottom board off the piano (push up on the flat spring(s) that are holding the board in place -- don't pull down!), you can look at the bass bridge.  It will be a curved piece of wood on the right side of the back, and it will have two rows of short steel pins stuck into it. 

All the strings in the bass section of the piano will be running over it, which makes it easier to find.  Each string weaves past two pins, which are under tremendous pressure. If the piano has gotten too dry, the pressure of the strings will have moved the pins and cracked the bridge.  A small amount of cracking is acceptable.  But if that bridge is in pieces, call your technician or say goodbye to this instrument and go look for another piano.



Almost any piano can be rebuilt, if you want it badly enough.  If it's a family heirloom that you love, then invest the money to make it play right.  If it's not, then think about other options.  What I've written and shown here are only general guidelines, so get more information if you need it.

But please don't ask anyone (especially a beginning player) to play a piano that is in bad condition or out-of-tune.  Get the most out of your investment, both in money and in effort, and keep that piano in good condition!

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Most of the graphics on this page were drawn by
Lonna Nachtigal, a fine artist from Ames, Iowa.  Thanks, Lonna