Diane writes: > Meanwhile I have a customer who wants me to replace the leather on the > hammers of his mid-19th century Bosendorfer. He wants it so bad that last > time I tuned he produced a chamois that he had purchased for the purpose and > asked me to cover them with it. We tried it on one hammer and it didn't > sound any good. > Chamois = oil-tanned = slippery, stretchy stuff. Not a good choice. Being mid-century, this piano is probably leather-covering over felt hammers? Schumann's Graf (1837) originally was all leather hammers. When brahms acquired it after Schumann's death mid-century, the hammers were changed to felt with leather coverings during a renovation. You want to use something similar to the softer leather I described above, for the outer layers of fully leathered hammers. The Viennese, in particular, were quite conservative, and when the builders started using felt they continued to use an outer layer of leather, because that was expected, not the new-fangled French felt thingies. Of course, there are advantages, especially in the treble, which is the part of the compass where leather continued to be used over felt for quite some time. > I now have a beautiful, soft, supple deerskin which sounded wonderful on > the Pokorney we rebuilt last Christmas and am wondering about putting it on > his hammers. > This could be a good choice. Check the characteristics I described in the previous letter. > Also there are questions about how to voice leather once it's > on the hammers. > You can do some touch-up voicing. Very gentle pliers will soften, alchohol/water will harden the outer leather. > Is there any other material that might be better than any leather? > Leather is pretty good all things being considered, if you use the right kind. > Would there be any material that would apply to the hammers easier and > quicker? > A good question, and an interesting research topic. No reason we couldn't find something that works, but it would still have to be tightly attached to the hammerhead in some way. Whatever is used, physical considerations demand the characteristics I described last letter. The aim is always a (nonlinear) compressibility gradation from low outside to high inside, as this is an important factor that defines traditional piano tone quality. This can be achieved by building up graded layers, as in leather hammers, or the layered felt used by Erard. Alternatively you can start with a single piece of material and manipulate it's characteristics by needling and other techniques, to build up the desired gradation. Microsopically the internal layers of material slide over each other as they are compressed, and friction and other internal molecular stickiness forces will play a role. When uncompressed, the layers of materials like felt do not respond in the reverse of how they were compressed, causing a hysteresis effect and loss of energy with each compression cycle. This is another important factor which defines piano tone. The primary advantage of leathering felt hammers is to increase their durability, rather than any specific tonal advantage. Leather top surface will probably last quite a bit longer than felt between voicings/replacement. And it's easier to re-leather the top layer, too, than filing and re-voicing plain felt hammers after they get too hard and cut. It might well be worth experimenting with leather-covered felt hammer, Diane, for your rental pianos, to ease your voicing labours. > Would there be any material that could be > put on the hammers temporarily to completely change the voicing for just one > concert? Perhaps a material that could be clipped on for the rock concert > and a different one for the classical concert? > Here you get into the realm of prepared piano. I would think these effects would be easier to achieve using mutation devices, like the moderator (woolen cloth), bassoon etc. on historical pianos. These sorts of special effects might be interesting to put back on modern pianos of new design, increasing their potential for "new music". > How could we measure the tonal differences of different materials? > It would not be difficult to design a tool to measure the non-linear compressibility characteristics of hammer coverings. Actually I proposed just such a project to one of our major piano manufacturers recently, but the offer was declined. As always it is just a question of desire and money. Such a device would be useful for techs and in the factory, especially for producing more consistent, higher quality hammers on the cheaper pianos. Also good for experimentation too of course. By extension this is an indirect measure of tonal quality, since tone is a consequence of the covering compressibility. > How would we know their life expectancy? > Put it on and bash away. Get students to practice with it. > How would we even find out about > materials that might be just perfect but they are used to build private > airplanes and we aren't even pilots, much less airplane manufacturers? > The history of technology transfer is not a straight road. That's what makes it fun. > These are questions I find interesting for their own sake and for the > practical need I have in my business. I will pursue the research project. > Please report on what you find, Diane. > My guess is that there are many other such questions burning in others' > brains. Can pianotech be a place where such research projects could be > shared? > Pianotech could be a forum for collective research like you suggest, but it needs participation and some some of organization for that to work. In the past we've has some good discussions on the list. My view is that we could achieve some good research results here by using the list as a resource for data collection, and experimentation, if enuf people would be prepared to participate and give us their hard-won results - someone will still need to put everything together. Stephen Stephen Birkett Fortepianos Authentic Reproductions of 18th and 19th Century Pianos 464 Winchester Drive Waterloo, Ontario Canada N2T 1K5 tel: 519-885-2228 mailto: birketts@wright.aps.uoguelph.ca
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