So do you think that the mass target for a given volume of wood always the same whether it's a low tension small piano or a high tension concert piano? If not, when would you shoot for a low mass versus a high mass panel? For those actually making panels, are there visual clues to what the mass is likely to be such that one could at least manufacture a board with consistent mass through the flitches (if that's important)? In a rib crowned type of system is the issue mass in specific areas of the board or is it the overall mass, the overall weight of the assembly? Finally, if you were building panels (or ordering them) what process would you use to identify the mass of either the panel overall or the flitches from which they are made and how would you define the target? I realize it's a lot of questions and the answers to these questions might be speculative but I'd be curious to hear your speculations if for nothing else as a guide for how to think about it on future projects. David Love www.davidlovepianos.com From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of Delwin D Fandrich Sent: Friday, February 11, 2011 8:52 AM To: caut at ptg.org Subject: Re: [CAUT] Hailun soundboards Interesting question. The really tight specifications that manufacturers have traditionally used for soundboard spruce are a holdover from the days when everything was viewed through compression-crowning lenses. Here the wood has to be selected for its ability to withstand relatively high levels of internal compression without showing undo signs of physical stress. The grain has to be as close to vertical as possible else, under long-term compression, the earlywood will shear slip giving the surface of the panel that familiar washboard look. Or, in more serious cases, severe compression ridges. The panel's ability to develop relatively consistent compression across its span and hold it for years is critical to the function of the soundboard. If, however, the stiffness of the soundboard system is obtained by other means-by using stiffer ribs, for example-then the structural demands on the soundboard wood are reduced to virtually nothing as it begins to act more simply as a vibrating diaphragm and other characteristics become important. (As long as solid spruce panels are used, of course, there will always be some amount of internal compression and/or tension within the panel as the seasons change.) As I think through the various parameters we have long used to specify our soundboard spruce I don't find the one that increasingly strikes me as being one of the most important: specific gravity, or mass. The workers who lay up soundboards in the typical piano factory sort through piles of spruce lumber to select wood with no flaws (for high-end pianos) or with relatively few and easily repairable flaws (for low-end pianos). They look for a reasonable color match within a panel, for reasonably consistent grain within a given panel (it might vary considerably from one panel to the next, however), for vertical grain deviation (although the definition of "vertical grain" is now fairly broad), etc. All of these are aesthetic characteristics having little to do with the performance of the soundboard. I can't recall a single factory that selects soundboard wood based on its specific gravity. Simplistically, a soundboard's impedance is a function of its stiffness and mass. Except for the compression-crowned (compression-stiffened might be more appropriate) soundboard system, the principle stiffening elements are the ribs and the bridges. Cross-panel stiffness is not particularly important; the ribs take care of that. Even longitudinal stiffness is not overly important; for the most part the bridges take care of that. Certainly the longitudinal stiffness of the wood boards making up the panel is a factor, but even relatively poor grade spruce is quite stiff parallel-to-grain. So what's left? It seems to me, mass. At first consideration it would seem that selecting for grain density would take care of mass but it doesn't. Two boards from different trees-which might well have come from different forests-having similar grain density can vary considerably in their specific gravity and, consequently, their weight. But, for consistency of acoustical performance from one piano to the next it would seem that the mass of soundboard panel is probably something you'd want to control. Anyway, to more-or-less answer your question, unless the soundboard panel is going to be placed under long-term compression it seems that mass and aesthetics are going to be the two primary considerations. Of the two far more consideration is generally given to aesthetics. Although, as you suggest, perhaps not enough. ddf Delwin D Fandrich Piano Design & Fabrication 620 South Tower Avenue Centralia, Washington 98531 USA del at fandrichpiano.com ddfandrich at gmail.com Phone 360.736.7563 From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of David Love Sent: Thursday, February 10, 2011 7:41 AM To: caut at ptg.org Subject: Re: [CAUT] Hailun soundboards Del: I see a wide range of appearance in the sitka spruce currently being used by what appears to be the most demanding independent builders especially with respect to grain density and such, at least with those who are employing non or minimal compression methods. So what are the requirements that make a piece of spruce "suitable" for soundboard making, in your opinion. David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/caut.php/attachments/20110211/e03b72ec/attachment-0001.htm>
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