(Fluid) Dynamic Trio: How a piano works
If you’ve ever spoken to me in person, there’s a good chance that I’ve told you about my love for piano in some way. There is so much that is involved in the production of sound within this beautiful instrument, and I think the best way to begin to understand it is through the actuation mechanism of each key.
To give a clearer image of what I’m referring to, I’ll reference the black and white Diagram 1 of the piano actuation mechanism. Each piano key (1) is actually a lever whose fulcrum is called a balance pin (2). When the musician strikes the key, the capstan screw (3) pushes up the whippen (4). The whippen itself is a beautiful little mechanism without which the piano would not be able to operate.
Let’s take a second away to admire this lovely image of a Steinway Grand Piano Whippen. It receives the downward motion from the piano key as it is being played, actuates the hammer, and helps to restore the entire system back to the original state. It is comprised of a jack (1), a repetition lever (2), a repetition flange (3), the main body (4), the whipping flange (5) (called jack(5) on previous diagram), and the main spring (6). This particular configuration has a butterfly spring comprised of two springs, with the actual repetition spring on top. There are several possible configurations for springs inside the whippen, for example the whippen in the gif has a single spring configuration. The repletion lever has a hole in it that allows the jack to pass through. This is crucial for the movement of the hammer, and ability of the piano to handle quickly repeated notes. The whippen is fixed to a point and hinged on one side (7), and free to move on the other.
With the end of that fun tour of a whippen, we’ll go back to refer to the first diagram again. Once the whippen is in motion, the jack (5) makes contact with and will roll the knuckle (6). The rolling knuckle will then cause the hammer shank (7) with a felt hammer on the end to begin moving upward. The hammer will hit the string associated with that piano key, and the vibration of that string is the tone that you hear when you press a key.
At the other end of the mechanism, the depressed piano key lever also raises a damper lever (12) that raises the damper itself (13) through a damper string. This action it what allows the piano to be capable of playing different lengths of notes. As long as the key is depressed, the damper will be lifted and the string is free to vibrate and produce a pitch. Once the key is lifted, the damper will fall back onto the string, stop the vibration, and end the note.
There is even more work to be done on the actuation side before the key is released. The motion of the jack (5) is stopped by the regulating button (8). The repetition lever (9) rises to a point where the jack passes through it and makes contact with the drop screw (10). This position is held until the key is released. As the hammer begins to fall, it will also cause the repetition lever (9) to fall which gives room for the jack to pass back through the repetition lever back into its original position. If you look at the gif of the entire mechanism, you can see that the repetition lever is lowered slightly after the hammer begins to lower, and that allows for the jack to pass back through it. As the hammer is lowered, the backcheck (11) prevents the hammer from flying up to strike the string again until the key is depressed again.
In cases where the music moves quickly and there is need for quick repetition, the mechanism will not reset fully to its original position in between strikes of the key. The hammer will move freely from the backcheck, and the repetition lever will remained up so that the whippen can be free to move the jack and in turn the hammer as fast as the key is being depressed. This allows for musicians to repeat notes quickly without waiting for the entire system to return fully to its original state.
Another fact that is incredible to me is that all of this is returned to the original state due to gravity. This is only the case, however, for grand pianos. The action is horizontally oriented in a grand piano, where as an upright piano’s action is vertical. That means the upright piano must rely on additional springs and mechanisms to restore itself to its original position.
All of this is still a simplification of the entirety of the mechanism that actuates the piano. Depending on the diagram you view and configuration of piano (grand vs upright) there can be 40 – 60 separate parts that comprise the final actuation mechanism. Each piano contains 88 of these mechanisms, one per key! And that’s just the actuation mechanism. I haven’t discussed the pedal system, or the composition of the body and strings yet. Even though I could probably write a novel about the piano, I don’t think my first blog post would be the place to start it. I hope this helps everyone have a greater appreciation for this incredible instrument.