hammers: what kind of felt?

[ari isaac]

    There are a number of felt types used for making hammers. When I order
felt for Isaac hammers I have the felt density vary from bass to treble to
affect a graduation of hammer impact accross the scale. I have always
thought this variation in hammer impact needs to correspond to the
variation in string taughtness.  The strings in the low bass, in effect,
run away from the hammer as soon as they are hit so that the hammer has to
allow for a deeper or extended push, or impact so as to deliver the desired
energy to the bass string.  The further up the scale the hammer impact
occurs - the less the string runs away from the impact due to its increased
taughtness. The impact and all it delivers, need to happen faster, in other
words, to take less time to complete. The graduated density of the felt
sheet enables the hammers to perform this graduated impact with a minimum
of monkeying with hardeners, irons and other forms of hammer torture, not
to say, technician torture.  A sheet of hammer felt of graduated density -
not merely graduated durometer reading - is a good deal more expensive to
have made.  You can see why hammer felt of uniform density throughout the
scale tends to be the norm.  Graduated density means, among other things,
that the wool fibers have to decrease in diameter towards the treble end. 
This nice feature of the felt sheet ensures not only a far more musical
piano tone but a huge increase in the voicing stability of the hammers.

Thank you for everybody's interest.  get in touch with me with anything
concerning hammers.    Ari Isaac