Interesting stuff as usual Stephen. I for one am really glad for your approach to all this, and that you take the time to share this with us through various PTG channels. If there was some kind of honorary membership for guys like yourself... I am very sure I would nominate you !! Cheers and thanks for your many contributions RicB .................... Some comments that appeared on caut list about the Askenvelt/Galembo article in the August PT Journal: >I wouldn't read too much into the results of the shank vibration >study because the vibrations were generated in an experimental setup. I think you mean "because the results were generated in an experimental setup that was not representative of the conditions pertaining in a real piano action in use". The hammers were clamped and driven by oscillators acting at the knuckle to determine the resonant frequencies. >As far as I know the different modes have not been isolated in real >piano playing. I also don't believe modes have been related to tone >production. The systems we're dealing with are incredibly complex, >and generating meaningful data is unbelievably difficult. Stay >tuned--there is more coming in future articles. As for the first point, we have observed hammer shank vibration modes in high-speed imaging of actions played under normal conditions. They are not easily seen on the upward moving hammer, because the speed is fast compared with the natural frequency of the shank vibration, so you only see a small protion of a cycle going up. Also the amplitude is rather small (ca 1-2mm effect on the hammer head). On the downward journey, as well as during contact, you can see a distinct oscillation under certain kinds of touch. Post-processing of the videos is effective at extracting the data on these modes of vibration. On the second point, that has yet to be determined. In fact, we don't really have a good understanding of the hammer-string interaction and how even hammer design affects it, so the effect of shank flexibility on tone would fall under that study. We are starting to look at the relationship between hammer properties (including shank) and the precursors of string vibration (those travelling pulses). This is actually a funded project that is just starting this week with a new PhD student. One final comment. The effect of hammershank vibration can be observed by the effect it has on causing hammer head to move (the shank/head glue joint is effectively rigid). This can change the contact footprint (scuffing). A 4ms contact, for instance, corresponds to a 250Hz cycle, so the shank vibration frequencies are definitely in the range where about 1 cycle or more occurs during contact with the string. If the amplitude is large enough and friction with the hammerhead and string is low enough you can typically expect motion in the order of 1mm during contact for a loud bow with a flexing hammershank. This scuffing we have observed with high speed imaging. We have also confirmed the frequencies with strain gages mounted on the top of the shank. All during regular playing of the key, not artificially clamped and driven hammershanks. (I've included this on the pianotech main list too, since it is a fairly general subject that may interest people not on caut as well.) Stephen
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