Hello Stephane, The problem of what exactly happens at impact in the string portion between the hammer and the agraffe/capo is complex, so I only speculate here: I don't know if it is the peak tension after impact, or the absorbed power that actually breaks the string. In a static measurement, we stretch a string very slowly and record the tension at which it breaks. In a dynamic case as we encounter in the piano, the stretching of the string is fast and the force is more like a pulse of limited duration. Is it the total energy transfer that matters here, or the peak tension? I don't know the answer to that, so the following is very much open for discussion. When the hammer hits the string, two pulses propagate along the string. One goes in the direction of the bridge, the other in the opposite direction, to the agraffe/capo. The pulse that goes to the agraffe is the shorter one of the two, but the peak tension is higher. So this pulse would be more likely to break the string if it's the peak force that matters more (regardless of the duration of that force). You would be right in his case, the string would break from the first impact. If it's the power transferred to the weak spot of the string that matters, I would guess (again, no math done here), that the pulse that formed on the section of string between the hammer strike point and the bridge will deliver more of it. What returns after reflection from the bridge may still be a substantial, relatively long pulse. Also, I was thinking about the observation that when you bend a piece of wire back and forth to work harden it, it will break when you try to "undo" the previous bend by bending it in the opposite direction. The reflection from the bridge causes a bending of the wire at the agraffe in the direction that is opposite to the bend of the wire as strung. Regarding the second point (regulation for maximum power transfer), my thoughts are as follows. There are two issues at work here: First, we certainly want an action that doesn't convert the player's energy into heat before it even reaches the strings. That means, we want to minimize friction where it doesn't help playing control. We don't want key sticks that flex too much. We don't want a capstan/wippen heel contacts that have more sliding motion than necessary. Also, excessive motion of the knuckle on the repetition lever/jack is suspect. (Except for Ron Overs' action, I don't know any that have minimized the amount of knuckle dragging - I am curious, why?). We also don't want balance rail felt punchings that are too thick and action center felt that is too compliant. The hammer shanks have to flex "just so" to aid the best energy transfer from hammer to string, etc... The second issue has to do with the efficient transfer of energy from the hammer to the string. This is a separate issue from everything that happened to get the hammer up to the string. Here, we have a difficult problem; we want as much energy transfer as possible to make the piano loud, but that may not give a good tone. I think the hammer dwell time on low notes is not sufficiently long to absorb the first reflection from the bridge. Somewhere in the mid/high tenor, the dwell time is sufficiently long in comparison with the pulse travel time that the reflected wave coming from the bridge is damped somewhat by the hammer. The shape, mass, hardness (and who knows what else) of the hammer will play a role here. I think, a good regulation will take care of all the factors that maximize energy transfer to the hammer, but some energy will be intentionally discarded in the hammers in order to find the best compromise between loudness and tone quality. Best regards, Vladan ================================== Hello Vladan. I would guess that the string is most > likely to break when the first reflection from the > bridge returns and hits the agraffe or capo. What makes you think it is not the first hammer-string contact that is the more offensive to the string ? How can the first reflection be more dangerous ? Before the first reflection, the first impact wave from the hammer strike point also reaches the capo, and with more amplitude than the reflection wave from the bridge, doesn't it ? The > magnitude of the reflection is a function of the > impedance match between the string and soundboard, so > it would seem possible that a piano with a high > reflection coefficient at the bridge is harder on the > strings. Ok. but still, I think the first shock is the more demanding on the string. As Andre mentioned, regulation and voicing > would also matter because the hammer dwell time > (string contact time) would have an effect on the > damping of the reflected wave too. Mmmm. But a well regulated action with well voiced hammers (at least the way André understands it) is meant to get the most power out of the string, thus again the most demanding, no ? Ok if the hammer blocks against the string, but this doesn't happen that much, does it ? In every other case, less well regulated action means less power transmitted to the string. But maybe you mean this is not about power ? Best regards. Stéphane Collin. __________________________________ Do you Yahoo!? Yahoo! Small Business - Try our new Resources site http://smallbusiness.yahoo.com/resources/
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