I know this is an over viewed type of topic but I may have some of my own input regarding touchweights.
As some may know, I've been struggling with my new D vs a 20 year old loaner D that I had for 2 months which had a seriously light touchweight of 38grams. (needs new hammers / has very light hammers).
My tech has been attempting to voice my new D so I would be able to get a very big dynamic range I could get from the old D but not from the new one.
The old D could easily be controlled all the way from a whisper to thunderous sound.
The initial direction was to get the hammers on the new D to be soft on the strike point but hard deeper for stronger blows. But I really light a bright sound out of my piano which required the strike point to be relatively hard.
My hunch was that voicing is not just about the density properties of the hammer, but the weight of the hammer itself.
I don't have formal education in physics but I'm usually pretty intuitive when it comes to things like that.
Lets pretend that on average, on an average piano, playing ppp would send the hammer to hit the string at 1m/s. A heavy hammer hitting the string at 1m/s would have much more momentum than a light hammer hitting the string at 1m/s. The lighter hammer is much more easily rebounded. Also QUICKER. This also means that the lighter hammer will spend less time in contact with the string as heavy hammer. THIS MUST EFFECT THE TIMBRE / VOICE OF THE PIANO.
The other issue is inertia. I hope I'm using the right terminology.
One of Nueton's law states something to the effect of a body at rest wants to remain at rest, and a body in motion wants to remain in motion. Meaning that to when I press a key, I must produce extra force to "free" it from rest, but once it starts moving, I will need much less force to keep it in motion all the way to the bottom of the key.
The problem is that the 10mm dip takes a fraction of a second to accomplish, and I don't know any piano player that can "break" the rest of the key, and let off pressure.
Here is an easier way to explain:
Have you ever pushed a very heavy shopping cart and to break inertia, you had to push very hard, but you weren't quick enough to stop pushing so hard, so the shopping cart now is way too fast? But to control the speed of an empty shopping cart is very easy.
I think the same applies with the action. Lighter action is easier to control. Is easy to play it softly, and it might be easier to play it loudly. After-all, we can exchange speed for momentum of mass. I bet I can make a light hammer move up faster than a heavy one.
So, if my theory is correct, the hammer must be lighter. But reducing a hammer by 1gram reduces the touchweight by 5grams at the key.
I am wondering, what is so wrong and frowned upon with super light action? I myself have NEVER played a piano and thought to myself "this action is too light". But countless times I felt "too heavy". Doing some reading, I found that historically, bigger hammers were being developed because pianists wanted more sound, to over power an orchestra etc, but not because pianists wanted to press harder on the keys.
So maybe I won't be able to play any other pianos if my downweight is 40grams, but the way I'm feeling right now, is that at least I'll enjoy my new piano. When I play a light actioned piano, even if it's old and sounds bad, I always feel happy. I don't feel like I fight the piano, but me and the piano are together on the same team trying to make music.
I read some people online who don't like light action, they want to feel the "feedback". What feedback? A piano is like a hammer catapult. You can't feel the string like on a violin or cello. It's not a steering wheel on a car or a yoke on a small airplane.
The hammers on my new D are absolutely enormous. Having seen enough hammers in my time, and also my tech has mentioned it many many times. The shoulders are very broad. Next time, my tech will cut them, then sand them to much smaller to decrease weight, and also taper the "tails" of the hammer. I think that will bring me down to low 40's from the 48 I am at now.