Resiliency

[John Hartman]

David Love wrote:
 > What do you notice happens on these boards with the softer more
 > resilient hammer when you try and get a very big forte?

David,

The use of the word "resilient" is confusing here. Resiliency is the
measure of a material's ability to recover its shape after being
deformed. The coefficient of resiliency (also known as the coefficient
of restitution) is measured in several ways. The classic method is to
form the test samples into spheres and drop them form a height onto a
massive surface like an anvil. How far the ball bounces back up
determines its resiliency. If it bounces back 90% the Coefficient is .90
for example.

Resiliency is one of the factors that determines what happens when 
bodies collide. A body with low resilience can not transfer much of its 
kinetic energy since most of it will be absorbed. A body with higher 
resiliency can transfer more of its energy since less will be absorbed. 
  It is bit more complicated than this but this is a major factor in 
what happens when the hammer strikes the strings.

I notice that most people use the word resilience completely opposite
from its true meaning. Most technicians think that soft felt is more
resilient that denser felt. What they are really talking about is
compliance. Felt is a fairly compliant material but is not particularly
resilient.

If you were to compare the resiliency of soft felt to that of more dense
hard felt made with the same fibers you will find that the harder felt
is more resilient.

Off hand I would have to say that one of the reasons felt is used to
make piano hammers is because its resiliency can be so easily controlled
by making it denser or less dense. The whole process of wrapping the
felt over the molding produces a hammer that is denser on the inside and
less dense on the outside. The less resilient upper surface of the
hammer will damp out more of the upper partials and absorb more of the
energy of the impact while the inner cores higher resiliency will be
more efficient and bring forth more overtones.

A lot of technicians are shock to here that lacquer increases the
hammer's resiliency. That's why it sounds brighter and louder.

John Hartman X-PTG

John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
Rebuilding Steinway and Mason & Hamlin
Grand Pianos Since 1979