And the debate on these last few pages has been about physics and math, rather than experimental evidence. (as an engineer I cringe over some of those posts - I do understand math and Newton - but it's not relevant)
As an engineer how you can make such a sweeping statement? What type of engineer? I'm going to detail the very real basis why it would be more improbable to think there is literally no variety possible in a very loud note played into a depressed pedal, than to feel that difference is possible. And if you're a genuine engineer who sincerely feels mechanics is irrelevant, then you can show your engineer balls by specifically debunking its relevance:
Anyway, I'm not going to go into the hammer itself but solely into the keybed thump. It is open to proof that this can be varied indepedently of the musical sound, which is why it would be staggering if it played no role in generating an overtone series, when acting forcefully into a depressed pedal. Also, while science can only isolate by working in single notes, this thud would logically be even more pronounced in thick chords. I've heard a concert where I could easily isolate all the thudding noises from the musical sounds, of a really badly percussive player.
Anyway, see the second group of diagrams at the start of this post:
https://pianoscience.blogspot.co.uk/2014/08/tonal-control-efficiency-and-health.htmlIn the situation where the knuckle is collapsing inward, it moves in faster than the key. Thus considerable energy is travelling towards collision without helping to generate any keyspeed. In the situation where the knuckle is expanding up and away, no arm momentum is necessarily sending any energy in the direction of collision whatsoever- thus there is much less of a heavy blow for the same level of hammer acceleration. The key is accelerated far more efficiently and with neglible momentum arriving at the keybed beyond that carried by the key itself. I can play very loud this way, without sending any arm momentum spiralling down into a thud- which some very bad pianists always do in even moderately loud playing. The more they collapse the hand towards the keybed, the more they have to send energy whacking into the keybed, despite the collapse also reducing how much sound they achieve.
Beyond any doubt there is scope to make notable difference in the energy level that collides with the keybed (as well as to choose whether that energy which does travel is allowed to continue into an aftershock, or be rebounded up and away from the point of landing). This is possible independently of the level of tone produced inside the instrument. It is completely irrational to suppose that there's only one intensity of thud which would always have to correspond to a given level of pianistic volume. Inefficient acceleration with considerable knuckle collapse sends vastly more energy towards collision, but fails miserably to translate the best part of the travelling momentum into hammer acceleration (due to the key failing to reach a speed that is as fast as the knuckle reaches in vain). And I didn't even mention the difference between a locked arm and a loose one, as a shock absorber.
So, perhaps you'd like to either rethink this nonsense or give a detailed description of why you as an engineer are supposedly in a position to casually dismiss these MAJOR issues from the very possibility of playing a role? On an empirical level, some experiments have indeed found differences and I've read some scientists saying that even Ortmann's data showed a number of visible differences that he chose to ignore. Given how much the thump can clearly be varied, it's madness to think that nobody could ever make enough difference to be recorded on a sensitive device, during loud attacks. Clearly, anyone who speaks of sound always being the same has simply made a subjective judgement of what is not literally "the same" but "same enough". That's not adequate science to hang anything on. Anyway, what is needed to make the differences truly unmissable on paper is that the volume must be extreme and the pedal must be held to be sure it will register in overtones too. No experiment which does not satisfy these requirements can be used to either "disprove" that an audible keythump happens in loud playing, or that a good player can soften it while still playing loud.
PS. To give another practical example, go and play a legato melody with a very short staccato but with pedal. Does it sound anything like the same as legato?