Ah, well, the grain angle of the soundboard panel—taken by itself—is important in only two parts of the scale: the high treble and the low bass. As you know a spruce panel is considerably stiffer longitudinally-to-grain than it is perpendicularly-to-grain. We want the upper end of the tenor bridge to see a fairly stiff load so up there it would be good for the grain to be perpendicular to the top soundboard liner. Following this down, however, we encounter the bass bridge where considerably more mobility is desired and having the soundboard grain angle perpendicular to the soundboard liner down there would further restrict the mobility of the bridge in an area where we really want the bridge to be able to move. To generate sound energy at very low audio frequencies you have to move a lot of air and that means the area around the low end of the bass bridge has to move. Since I was “floating” the low end of the soundboard panel—adequate freedom of motion was a given—my requirements for soundboard grain angle could be concentrated on the needs of the treble section. I extended the treble soundboard liner up some—giving the bridge plenty of room to move—but controlled that motion by using a somewhat unusual soundboard grain angle. ddf Delwin D Fandrich Piano Design & Fabrication 6939 Foothill Court SW, Olympia, Washington 98512 USA Phone 360.515.0119 — Cell 360.388.6525 <mailto:del at fandrichpiano.com> del at fandrichpiano.com — <mailto:ddfandrich at gmail.com> ddfandrich at gmail.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Gene Nelson Sent: Saturday, May 19, 2012 7:22 AM To: pianotech at ptg.org Subject: Re: [pianotech] S&S K(52) Restoration I appreciate the explaination, thank you How does the steep grain angle of Terry's board fit into the stiffness/mass transition scenario? Seems to me the treble would be especially stiff Gene Sent from my iPhone On May 18, 2012, at 10:45 PM, "Delwin D Fandrich" <del at fandrichpiano.com> wrote: Look at the drawing below. <image003.jpg> Ribs #2 and #4 extend across the width of the working portion of the soundboard. The low end of the bridge has an extension that goes over the floating portion of the soundboard liner. These three ribs provide all of the stiffness the area around the bass bridge needs. The rest of the ribs are all sized to provide the necessary stiffness to the area around the tenor/treble bridge. In the Fandrich piano the ribs that terminate in the Z-Bar—i.e., ribs #5 through #13—are set into notches in either the Z-Bar or the soundboard cutoff bar. The lower ribs—#1 through #4—terminate about 10 mm in from edge of the soundboard panel. The M rim set up against the soundboard assembly do highlight the Z-Bar but this is not quite how the Z-Bar works. The Z-Bar presents a very rigid termination to the soundboard panel in the area around the treble end of the bridge. The further down the scale you go the Z-Bar its termination impedance decreases—its stiffness decreases--allowing the edge of the working portion of the soundboard to move with increasing freedom. The termination impedance of the soundboard panel varies with the frequency of the energy waves traveling across the soundboard assembly; the fundamentals and lower partials are affected more by the stiffness—which is decreasing down the scale—of the Z-Bar while the higher partials are affected more by its mass which also decreases further away from the point where it is solidly fixed to the back assembly. The soundboard assembly actually appears larger to the fundamentals and lower partials; smaller to the higher partials. In practice this has the effect of increasing the dynamic range of the instrument through the tenor section of the piano. The Z-Bar also adds both stiffness and mass to the area around the tenor end of the bass bridge. By coupling the ends of the Z-Bar and the bass bridge together the bass bridge extends the effectiveness of the Z-Bar further down the scale keeping the effective area of the soundboard relatively smaller than it would otherwise be which improves the efficiency of the soundboard around the low end of the tenor bridge. The bass bridge is able to take advantage of the entire soundboard area in the lower half of the soundboard assembly. That’s the short version and I think I got it all straight. It’s late and it’s been a very long day—I’ve been moving shop equipment and tools and other stuff—so I’m not guaranteeing anything. I’m sure if I got something turned around someone will be happy to point it out to me…. ddf Delwin D Fandrich Piano Design & Fabrication 6939 Foothill Court SW, Olympia, Washington 98512 USA Phone 360.515.0119 — Cell 360.388.6525 del at fandrichpiano.com <mailto:del at fandrichpiano.com> — ddfandrich at gmail.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Gene Nelson Sent: Friday, May 18, 2012 5:26 PM To: pianotech at ptg.org Subject: Re: [pianotech] S&S K(52) Restoration Great pics Terry, thank you. Getting your cauls up off the floor is a nice feature. I am having trouble seeing just how the bass bridge is supported with ribs?? Did all of the ribs get notched into the rim/Z-bar assemblies? The M frame highlights the Z-bar frame nicely – great way to visualize the concept. _____ -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20120519/8e3820c0/attachment.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC