How piano actions work
The journey to superb sound
The key is pressed, setting the action mechanism into motion.
Normally, the fronts of the piano keys are the only parts of the action that pianists see. It’s almost a shame they don’t get to experience the rest of this marvel in wood, felt, and leather.
The capstan in the key transfers the energy to the wippen.
The capstan is designed as an adjusting screw; it is used to set the functional dimensions precisely.
The wippen has three sub-functions, which are performed by the mobile components within it: the jack, the repetition lever, and the lever spring.
First, the motion of the key is translated into the corresponding lever and then onward.
Second, the jack and the repetition lever set into motion, which tightens the lever spring.
Third, once the backcheck is triggered, the lever spring returns the hammer to its ready position.
When the jack moves, it touches the let-off button, which catches the hammer’s motion toward the string at just the right moment so that the hammer drops freely against the string. That is what makes the piano’s full dynamic range possible, from ppp to fff.
A felted adjusting screw used to set the distance from which the hammer hits the string.
The hammer shank and its leather-covered roller rest on the repetition lever. Everything about these components is designed to transfer the force with soundless sensitivity, from the key to the hammer head and then ultimately to the string. Its movement upward is hindered by the repetition screw, which creates a kind of “plop” feeling in the key. That feeling is important, because it indicates where the softest attacks should be possible when the key is perfectly regulated.
The shank and head of the hammer need to be bonded as firmly as possible, in order to ensure optimum transfer of the force to the string. The hammer shank is secured to the frame of the action with a flange, so that the head will always strike the string exactly where the designer intended.
After all the energy that was applied to the key has been translated through the wippen to the hammer shank, it reaches one of its final stations on its journey to the string. The hammer head is made of wood hard enough to withstand that energy, felt (which needs to be firm yet elastic in order to shape the sound), and a rivet to secure the glued areas. Good piano technicians can adjust these points to get the most out of the instrument’s sound.
Lower notes have longer (copper-wrapped) strings; higher notes have shorter strings. Between one and four strings are struck for each note, depending on how loud the player wants it.
After it strikes the string, the backcheck on the end of the key holds the hammer in a kind of holding position. The key moves down at the same time as the hammer moves up, which causes the lever spring to tighten. Once the key is even slightly released, that spring allows the hammer to lift up from the position the backcheck is holding it in, so that it can strike again. The player will feel a certain “pull” in the key at that moment.
At the same time as the wippen sets into motion, the damper lever is lifted from the end of the key. The damper is attached to it with a wire.
The damper’s job is to absorb energy that has been transferred into the string. The damper’s own weight brings it down onto the string, and its soft felt mutes the vibrations.