Inertia, was "Grand Touch"

[william ballard]

On Jul 12, 2006, at 1:13 AM, V T wrote:
> There is a fundamental trade-off between balance
> weight and key stick inertia.  If we add a lot of lead
> to make the balance weight low, the action will feel
> very light, but only when you move the key slowly.  If
> you try to play a loud note, all that lead will have
> to be accelerated and the key will feel heavy.

Thanks for the clarification, Vladan. It's also useful to keep in  
mind that the trade off between BW and FW, is actually a balancing of  
two separate but equal forces (US Supreme Court Brown vs. Board of  
Education does not apply here). They are the net static force of  
gravitational attraction on either side of the key (BW), and the  
dynamic force of inertia (for which FW is a reliable analog). The  
former is the difference between the load on either side of the key,  
and the latter, the sum.

Stephen Birkett gave a good explanation (2, maybe 3 years ago) that  
while the net force of gravity on the key (oh, yes, not to forget  
force of friction...) determines the threshold force required to set  
the key in any motion whatsoever, the FW required to bring that  
threshold force down to something practical will also determine the  
increasing levels of force required as you ask increasing levels of  
acceleration from that key (and coupled parts).

At about the same time, someone else on PTx ( a David, I believe)  
described a device which would read key inertia by attaching it to a  
vertical, zero-friction spindle which was coupled to springs.

Mr. Bill