What is the difference between Overdamping and Underdamping?

[FAQ's]

Overdamping is a system whereby the piano damping mechanism (the bit that shuts the piano up) is situated above the hammer strike line. Underdamping is where the piano dampers are placed below the hammer strike line. Advantages and disadvantages. Overdamping. Imagine an elastic band three-foot long, you twang it and then put your finger near to the end of the elastic band, to stop it vibrating. This is overdamping.

Take the same elastic band and place your finger near the centre to stop it from vibrating this is underdamping, which of course is more efficient. Overdamping is controlled by gravity where as underdamping is controlled by adjustable springs so on the whole underdamping is far more efficient than overdamping. However, there is one disadvantage with underdamping. That is, if the dampers are incorrectly aligned to the nodes and antinodes of the vibrating string this will result in, the dampers when they come in contact with the string, emphasising certain harmonics on the piano, thus giving you a harmonic ring, this is more common on small uprights and small grand’s as the margin of tolerance decreases as the piano becomes smaller.

Robin Foster MABPT
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