The physics inside piano website

July 22, 2007

From where the term Action comes from? what is the real meaning of this term?

in which way was developed and how has been the evolution of this device?

technicians use the slang term Action to identify the gears inside the piano, what do they exactly mean? ... action in physics is actually a meaningful concept:

In fundamentals physical constants Action is expressed as (Energy) x (time), (mass x lenght2 ) / (time) , etc.

animated gif courtesy of K. Wayne Land.

The inventor of pianoforte in up XVIII century was the italian Bartolomeo Cristofori (Tuscany 1655 - 1732), he was a famous luthier constructor of spinets and harpsichords and he had the intuition to project a system of excitation of the strings somewhat original:

No more a mechanic plectrum and a lever as in the instruments that up to then were constructed (spinets, harpsichords, etc.) which did not permit to play legato, instead he conceived a mechanical system with which the string receive the excitation impulse from the bottom, similar to a pebble launch from a sling: in opposition to gravity force. Therefore he called his idea: " Gravicembalo with-the-piano and with-the-forte ". Cristofori called his new invention "Gravicembalo" not because regarding its predecessors it was an instrument more able to emit grave low bass sounds, but because its operation is set up fundamentally on the gravity force. In other words on the weight, not only the weight of the opposite elements to the gravitational force that excite the string, but also of the weight of the shoulder, arm, forearm, and hand of the pianist that striking the key acts towards the center of the earth. In the will of counterbalancing and equilibrium of such two weights at playing, a broad extensive availability of mechanical configurations is opened, which incorporated to gesture movements and harmonious sounds render possible to express infinite shapes of feelings and states of mind. Above animation appears here as a courtesy of Professor K. Wayne Land . Do not reproduce or hyperlink to this file without asking the permission of creator.

That should be and is the meaning of "piano Action" for physicists: Not the gears alone but an amount of mechanical energy that leaves from the pianist hand and flows for a time period through a mechanism towards the string. All this trasfering of energy is achieved in interaction with the gravity force. Nothing new under the sun, but one notes that this is exactly to say that acoustic pianoforte is closely a gravitational instrument in a rather wider sense ...

The invention of Bartolomeo Cristofori succeeded to overwhelm the demand of musicians of that time, they not only wanted a new brand instrument with more depth of sound than clavicembals but, especially, with more expressive dowries.

There are 74 components in the grand-piano action. Functionement and design of upright piano action is completely different. In all pianos action components are grouped in five main rigid body coupled elements (colored):

The five rigid bodies of piano action

The evolution of this mechanism happened through some decades long metamorphosis, with important improvements made by other European inventors, among others Johann Andreas Stein who developed the Viennese action (1728-1792) in Germany, and Sebastian Erard (1752-1831) in France who patented the nowadays standard double blow mechanism in 1821. Upright piano action was invented by the italian priest Domenico Del Mela in 1739. There are pretty epoch images in this website hammerfluegel. Some chronology remarks are visible here .

This is a harpsichord plettro mechanism draw:
harpsichord action

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