Adjusting wippen assist springs

[Sarah Fox]

Hi Ric,

<<Of course the problem with this idea, is that springs do not in reality
determine touchweight, they only alter touchweight gradient.  The assist
spring simply applies an upwards force which remains a constant.... say 20
grams. Now if you are using 50 grams of force for a very quite touch then
this 20 grams counts for something...  about 30 % of the total lifting force
of 70 grams... if however you are playing hard and apply a force of say 200
grams... then suddenly this spring is only helping your finger our with 10 %
of the work.  And as you get into really heavy play the spring has even less
effect. >>

This is true, but only if one looks at the input side, without regard to
output.  With greater spring assist and less leading, that same 200 g of
force will produce greater hammer velocity and therefore more sound.

How?  If a greater proportion of your counterbalancing is done by spring
force, rather than key leading, there is considerably less inertia to fight
in the key during hard playing.  Remember, the kinetic energy of the hammer
is transferred to the strings (to a greater or lesser extent, depending on
the resiliency of the hammers), while the kinetic energy of the keystick is
transferred into the front rail, where it makes no sound but a "thud."  The
higher the ratio of hammer inertia to keystick inertia, the lesser the input
energy that must be delivered into the key to transfer a given amount of
energy to the string.

Peace,
Sarah