William, I'm a relative newcomer compared to others who I hope will join in to clarify or refute. My perspective is that of a mechanical engineer turned piano technician. But as I see it, crown is a means, not an end. In other words, what you need from a soundboard is appropriate stiffness/mass/impedence that endures for the life of the piano. ( Refer to archives about impedence matching SB stiffness to string wt/frequency in the different regions of the SB.) Crown is a construction feature which, in combination with traditional materials and design features, tends to produce the desired effect. There are other ways to achieve this, including Del's epoxy surface coating. I have noticed, in my brief career, big improvements in treble power, clarity, and sustain in small pianos, without doing anything about crown. What you do have to do: re-attach separated ribs, shim or fill SB cracks, cap or epoxy the bridges, install new bridge pins, re-surface the v-bar and agraffes. Control your shop humidity at the lower end of the normal seasonal range. Trying to put crown back into an old board by radically drying before shimming, or pushing up on the underside before shimming, only ensures that during next summer's high humidity the soundboard will compress and crush, and the following winter the cracks will come back. Bottom line: if you want more crown, install a new board and/or new ribs. If you want to increase the stiffness of the existing board, try the epoxy surface treatment. If you want noticeable improvement with low risk, do the basics with precise attention to detail. JMHO Mike > [Original Message] > From: William R. Monroe <pianotech@a440piano.net> > To: Pianotech <pianotech@ptg.org> > Date: 3/13/2005 7:42:17 AM > Subject: Increasing Crown > > List, > > I am currently working on rebuilding my own little piano to gain some > experience, and have a question about improving the crown, function of the > soundboard. I had heard of shimming up the SB from underneath, prior to > shimming, or doing anything else on top (Bridge repairs, etc.), in hope that > by doing these repairs while the board was shimmed up, they might act to > improve the crown, even a very little bit. > > My question is about flowing epoxy over the surface of the board, as was > discussed here a while back, and I'm wondering what you all think about > having the board wedged up & flowing on epoxy. My concern is about what may > happen when the wedges are removed - cracked epoxy?!?!? > > What say you? > > William R. Monroe > > > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives
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