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Rotational Inertia…Kinetic Energy

Posted by glenbarkman on October 18, 2009

rkeI’m the first to admit, i’m not into physics – not to say i don’t enjoy it, but i’m untrained in the area of advanced physics.  What i AM interested in though is the practical application of physics – more specifically the touch of the piano.  A few years back i had a Yamaha C5 in my shop.  Beautiful instrument.  It was apparent however that the touch was simply ALL WRONG.  It had been monkeyed with.  So i applied usual regulation specs and it turned out nicely.  However, there was one niggly thing sitting in the back of my head that just wouldn’t go away… and that is that the instrument felt somehow sluggish.  At the same time i had been looking over some ideas on key weighting which is the concept of adding/removing lead weights into the keys to achieve a more balanced keyboard.  For those who are unaware, key weighting is a common practice in MOST pianos.  The key weighting is part of the balancing of the equation to achieve a certain initial weight at the outset of the key.  (And if you don’t believe me, next time you’re near a grand, press down a key and look at the neighbouring keysticks – you may just catch a glimpse of a circular led weight inserted into the key. )  Anyhow, for kicks i thought that i would key weight this C5.  Sure enough the touch improved dramatically.  End of story? Nope… i was still bugged by that same sluggish feel.  So i rechecked my work and i must say that at soft playing, the piano was EXCEPTIONAL.  It wasn’t until you hit the fast notes that i noticed the problem.  Well… the piano ended up selling but that problem lingered in the back of my head. 

Fast forward 3 years.  I have a client who is an engineer.  We were speaking about physics, touch of the piano… and he just so happened to mention Kinetic Energy.  I had a small epiphany… i thought to myself… IT DOESN’T REALLY MATTER HOW MUCH KEY WEIGHTING HAPPENS BECAUSE THAT ONLY REPRESENTS THE HAMMER AT REST POSITION.  AHA! No wonder that piano felt great at soft volumes – there was little inertia and the key weighting was ‘closer’ to the ‘at rest’ weight.  So… the ONLY way then to affect touch is to change the mass.  Ok gears turning here… if i could measure the velocity of the hammer in travel (ie radar, infrared beam etc) and the weight of the hammer i can measure… then i would be able to calculate the Kinetic Energy.  What that means then is that one could ‘reverse’ model the ‘feel’ of great pianos.  The rotational radius is similar as pianos have become more standardized.  The combination then of calculated KE and key weighting would make for an undeniable touch don’t you think?  So if KE=1/2MV2… we know mass… if only i could determine velocity… hmmm… thinking thinking… could i borrow my cop friend’s radar gear? lol.

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