Historical Keyboard Collection
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Beethoven Center
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Technological evolution of the keyboard
from the clavichord to the Erard 

The clavichord, which dates from the 15th century, is mechanically simple: when a key is depressed a metal tangent in the back rises “teetor-totter” style and contacts the string to make a sound. When the key is released, a felt strip to stop the sound, dampens it. Since the downward force of the finger keeps the tangent in contact with the string, changing the amount of pressure from the finger can create a tremolo effect. This effect called bebung, is impossible to emulate on a harpsichord or a modern piano.

Early Clavichord hammer action
In this photo, the metal tangent, third from right, rises to meet the string. The red felt strip above it dampens the string and stops the sound

 

Harpsichord hammer action
Here is a view of the jacks (white rods with green flags) and quills that plucked the string, making the harpsichord sound.

 

Hammer action of early fortepiano
Here is a view of the internal mechanisms of the Poletti-Johnson fortepiano, in which hammers are used to strike the string. This is representative of the single escapement mechanism.

 

Internal mechanism of Erard grand piano
This is a photo of the internal mechanism of the Erard grand piano dating 1875. If you compare this action to the action of fortepianos, you will immediately notice it is much more complex.

 

Erard Grand piano stabilizing and tuning bars
This photo of the Erard shows both the stabilizing bar as well as the horizontal brass tuning bar.
 

 

The quiet delicate sound of the clavichord, though charming, is also its chief drawback. It can only be enjoyed as a solo instrument in very quiet surroundings.

As it’s name implies, the harpsichord, is in some respects a mechanized harp with keys and a mechanical action which replace human fingers that would normally pluck the strings. The device connected to the key which plucks the string is called a jack. The jack moves up-and-down in a vertical plane with the stroke of the key. Inside the jack is a small horizontal part called a quill that plucks the string. The quill is mounted on a movable pivot called a tongue that allows the quill to pluck on the upstroke of the jack and then slide past the string upon the release of the key. A felt mounted on top of the jack quiets the string acting like a damper in a piano.

Early harpsichords were designed with a scale of one string for each key. A special characteristic of the harpsichord is its lack of variable dynamic range. Unlike a piano, the amount of downward force on the key makes little or no change in the volume of sound when a note is played. Inventors sought to increase the dynamic range of the instrument by adding multiple choruses of strings, which could be engaged through the use of either levers or pedals. Thus in the course of a performance, dynamics could be modulated by engaging or disengaging a chorus scale.

The different choruses of strings have been identified along the lines of the ranks of organ pipes. Most harpsichords have one or two standard choruses set at what is called 8-foot pitch. These would correspond to organ pipes of the same pitch that are 8 feet in length. Some instruments have a chorus which sounds an octave higher designated as 4-foot, and in rare instances some instruments even have a chorus of longer strings corresponding to 16 foot pitch which sounds an octave lower than the standard 8 foot pitch. 

Bartolomo Christofori of Padua, Italy, is credited with the invention of the piano. His early instruments were similar in size and construction to the harpsichord but with a hammer action that struck the strings. Christofori applied a physical principal from clock making to develop his new device which we call escapement. After the hammer hits the string, it will rebound and reset for another blow. Johann Andreas Stein improved upon the Christofori action design. This type of action became known as the Vienna action and it remained in use until the 20th century. Both fortepianos at the Beethoven Center have actions of this type.

The Erard piano has a mechanism called the double escapement repetition, allowing the hammer to reset for another blow (to the string) by the slightest release of the key. The butterfly spring supporting the mechanism is what allows this to happen. In the Viennese action the hammer will reset only of you release the key completely. By the early 20th century, the Erard action supplanted the Vienna action. 

Another important invention was the use of metal stabilizing bars that ran parallel to the length of the wooden case. These bars serve to reinforce the case and provided the strength needed to counter the enormous tension created by the strings. The agraffe, another Erard device is a small square metal peg through which the strings are threaded at one end of the piano. This device stabilizes the tuning of the piano. Finally, the Erards installed a metal horizontal bar that was placed across the strings in the treble register that also contributed to keeping the piano in tune.