From touch to
string vibration

Anders Askenfelt & Erik Jansson

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This lecture will present a series of experiments exploring the initial stages of the sound production in the piano - beginning with the motion of the key and ending with the string vibrations. This chain of events is closely connected with the performance of the pianist, who, by depressing the key, sets the parts of the action in motion, which eventually causes the hammer to strike the strings.

In contrast to performers on other string instruments, like the violinist or the guitar player, the pianist could be said to only have an indirect control of the string excitation. Using the computer biased terminology of today, it is tempting to call the action an "interface" between the pianist and the string. This interface is an interconnecting device, which at the input end (the keys) is particularly adapted to the soft and sensitive fingers of the pianist, while the output end is equipped with hard felt hammers, capable of exciting even the thickest of the tense piano strings vigorously. The function of this "interface" in playing is by no means simple.

We will illustrate some important properties of the action by presenting measurements of the timing in the action under different conditions, and also show how the motions of the key and hammer change, depending on how the key is depressed. Furthermore, the resulting string vibrations will be closely examined and the manufacturer's, the piano technician's and the pianist's influence on the spectrum of the piano tone will be compared.

During the presentation it will successively become clear that the successful piano performer is accompanied by two mostly anonymous artists, the piano technician and the tuner, sometimes but far from always combined in one and the same person. In contrast to a widespread belief, the fact is that it is not sufficient to have the piano tuned prior to the performance (in such a way that it stays in tune during the entire concert); the piano must also be properly regulated in order to play well.

Despite the remote control of the actual string excitation by the hammer impact, pianists pay great attention to the way the key is depressed. Often the term "touch" is used to denote this process. Physicists and piano players have had contrasting views regarding the importance of this point for a long period of time, and later on we will try to add some material regarding this question. However, we must hasten to add that at the moment we will not be able to resolve this conflict, but perhaps we can indicate in which directions the answers can be sought.

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This lecture is one of Five lectures on the Acoustics of the piano

1990 Royal Swedish Academy of Music