Ric rote: >Grin... prodding is what I do best me thinks... so let me prod once more. >You seem to make the clear statement that internal friction moments >are critical to the sound resulting in the piano when a felt hammer >hits the strings.... tho you dont go much into detail as to the >hows/whats/whys... perhaps understandably so... but since this >tangent of the discussion seems intent on comparision (for not to >say competition) between <<lacquered up>> and <<needled down>> >hammers it seems central to ascertain whether or not either approach >results in anything particularilly negative in relationship to this >internal friction capacitance Methinks that "you" is me. A little backtracking is necessary here....my research so far has related primarily to the felt material itself, trying to understand the dynamics of felt compression in isolation of the various complications that come from the use of felt in the context of piano hammers. The cart quite clearly needs to go before the horse when working with a material as bizarre as felt (or leather). We're also in the process of exploring the effects on felt dynamics due to procedures like needling, tensioning, heat and pressure, softening agents, and including lacquering. This work still focuses on felt pieces rather than hammers so that the effect of each procedeure can be studied separately with targeted experiments. The next step (which we want to start on now) is to study the application of felt in hammers, comparing different manufacturing techniques, and especially approaches such as being discussed in this thread. So Ric, Topperpiano, Dale, et al, you can see its a little early to be able to go into too much detail yet, if only because it's work in progress. I'm convinced we need to understand the material and processes separately, before we'll have any real understanding of hammers. The work will all be published eventually. >The following quote from Bernhards last claims authority on a a >related issue of this subject matter... > "Measurements on hammers parameters has been done by Anatoli Stulov, > where he measured felt stiffness and rebound time.He found > differences of a factor of about 100 % in the rebound time between > different new hammer sets made by diverse makers. (Abel, Renner, > Imadegawa) > The rebound time is in correlation with the felts /inner friction > losses/ (or imaginary part of elastic modulus) , not to /stiffness/. >Which states outright that rebound time is not correlated to hammer stiffness. I'm not familiar with any Stulov article which reports what Berhard has indicated above (maybe it's not published). But, in one of Stulov's articles he states: "...it is obvious that the dynamical features of the hammers produced by various firms are very similar indeed, for the various rates of loading. Thus we may state that in spite of the different technologies that the manufacturers of the piano hammers are using, the mechanicaI features of their hammers are rather comparable." This is in reference to the three types of hammers (Abel, Renner, and Imad.). Those comments, at least, are not consistent with major differences reported above. I would expect *both stiffness and internal friction to be relevant to rebound time. On the other hand, I'm not convinced that rebound time per se is the important factor that needs to be given such prominence. >So my prodding leads me to ask do you agree with the quote... See above. >and would you say that the addition of lacquer has any affect on >this internal friction, and if so what... and the same question >again with respect to needling. I have yet to do those experiments even for felt itself. But I would be surprised if both of these do not affect both stiffness and internal friction....in other words the loading and unloading curves are independently controlled by needling and/or lacquering. The effects on felt vs hammers will, of course, be different too, and need to be separately studied. Here's an interesting example illustrating a point. There's a quite large difference in the dynamics of a piece of felt vs the same piece cut into two layers and re-assembled. The latter will never behave like the former. Or, equivalently, layered felt stacks with identical felt behave differently according to the number of layers (even after factoring out the thickness). Now consider needling and lacquering and go figure.... One point that's also worth mentioning. All of the work you see reported on "piano hammer felt" is actually working with piano hammers as objects, not felt itself. These are typically struck against immovable surfaces, which don't necessary have the shape of strings. Also the manner in which "forces" and "displacements" are measured can have a dramatic impact on the interpretation of those variables, and the results. Unfortunately, these things are very often not disclosed, let alone discussed, in articles (one of my beefs against Stulov's articles for instance). Stephen -- Dr Stephen Birkett Associate Professor 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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