Ric prodded: >An interesting point that I see no one has really answered too. Well I'll weigh in on this interesting discussion. Having spent months chasing hundredths of a mm in myriad felt compression experiments I feel like I'm getting to know the stuff all too well. And very strange stuff it is. Some collected comments.... Bernhard: >Hammers parameters are not only stiffness/springieness. >A big influence on sound quality is the amount of the energy that is lost >due to the hammers inner friction of the fibers. I agree, but those internal energy losses are critical to defining the action of the hammer as it initiates string motion, before any standing wave can be said to have developed. In other words they define the signal which is imparted to the string and which eventually develops into the complexities of the waveform. If the hammer leaves too soon (e.g. a rigid block of steel hitting the string) there is no time at all for it to influence the sound and the result is bland and uninteresting. Even with a properly voiced hammer there are only a few ms during which ALL the information it can give to the string has to be imparted, so we don't want to shorten that contact time too much. We want the goldilocks effect as was alluded to by someone earlier...the hammer must stay on the string not too long and not too short, but just right. Within that window of opportunity there is a huge palette of adjustment waiting to be exploited....this is the effect of voicing and other factors that can be adjusted in hammer design, and the relation of hammer and string. Apart from the error that rebound time should be minimized, the next important mistake is that hammer-string contact is not simply on or off anyway. In the few ms of obvious contact there is a continuous range of very large force changes occurring in the hammer felt, corresponding to a continuous range of on-off condition between physically disconnected and obviously maximally imbedded. Even the concept of multiple contacts (e.g. as described in the 5 lectures) is too simplistic to be of real value in describing the hammer-string interaction. So where does that leave the poor hammer designer? Dale: > Which no doubt is in direct correlation with it's inate stiffness >/sprininess or lack of it. No. 'Springiness' can be adjusted independently of internal friction. I've seen this in simple felt slabs of different types, let alone in a piano hammer with all the other design factors that can be manipulated to change the parameters that affect string interaction. Bernhard: >A good felt quality has a high ability of rebounding a big amount of >the input energy. >It seems logic that this rebounding ability on a high quality hammer >is reduced by >lacquering. Certainly we can look at the felt material itself and try to understand its behaviour...as I've been doing for months. What we do with that felt - even if we can say meaningfully that it is of low, medium, or high quality - using it in a hammer design is another matter altogether, so even if we know everything we want about the felt itself, and can quantify its quality as "high" in some sense, that is not enough to guarantee it will be "high quality" in any sense on a hammer. The best felt may produce a crap hammer, and possibly even vice versa to some extent. Both felt and hammer design have to work together to give the parameters considered desirable in a good hammer. On the last point above, I don't see any logical connection between lacquering a "high quality hammer", internal friction, and reducing rebound time. I think the jury hasn't even gone out yet on this one....hence the constant banter back and forth between rival camps. and Dale: >May I submit that the Inner friction of felt has always been a >fairly esoteric & small consideration to the discussion of hammers >even though it is a know factor & frankly to me personally not very >useful. I disagree. I think this phenomenon is actually the contributing factor which will turn out to be MOST critical and absolutely essential to felt hammers being able to produce the sound we have come to expect from the piano. Without it the sound would probably be considered wrong and un-piano-like. I have some ideas why, and how, but won't speculate yet on what we may find as we will soon be extending the felt research project to consider hammer design and hammer-string interaction. Stephen -- Dr Stephen Birkett Associate Professor Associate Member, Piano Technicians Guild, Department of Systems Design Engineering University of Waterloo Waterloo, Ontario Canada N2L 3G1 E3 Room 3158 tel: 519-888-4567 Ext. 3792 fax: 519-746-4791 PianoTech Lab Room E3-3160 Ext. 7115 mailto: sbirkett[at]real.uwaterloo.ca http://real.uwaterloo.ca/~sbirkett
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