The New Touchweight Metrology
As piano builders and rebuilders, we have inherited a crude and archaic system for measuring the balance of the action mechanism. The weight of the hammer, which sits out on the end of a long lever arm and has such tremendous influence on touch and tone, is measured in weight to the nearest pound of a sheet of felt from which many sets of hammers are made. We assume the proportion of key-to-hammer movement is roughly 1:5, but we have no reliable means to accurately measure this ratio or detect leverage problems. The keys are "balanced" using downweight as a primary indicator, but “balance" implies a state of static equilibrium, and downweight is taken from the moving key.
We know that when a piano is built, the weight of the action parts sitting on the back of the key exerts an upward force at the front of the key, which is too high without the addition of keyleads to the front of the key. What is the effective weight of the action parts? How does their weight translate to an upward force at the front of the key? How much is the downward force at the front of the key? Conventional wisdom simply does not provide answers to these important questions.
Steinway has not only changed the geometry of their actions over the years, but also the weight of their hammers. Therefore, when installing genuine Steinway components on an older instrument, it’s not a simple matter of exchanging out the old components for new ones. With new parts comes new action geometry ratios. To keep the same touch and weight of your instrument, an intimate knowledge of action geometry is a must. Let us talk to you about what is involved in restoring your Steinway to its original feel and response.