Hi JD Sorry for the late reply. Too many distractions since May, Our house was robbed 2 months after my bro's died, my sister now has cancer and in hospital with a broken leg and now my Dads is living with us...whew. IS that enough. Any way I am not ignoring some questions asked last week but the Erwin's have had their share of difficult life circumstances this year. Dale At 01:23 -0400 15/7/10, Dale Erwin wrote: JD write----Hello Dale, Looking at your pictures of the board, I'm curious to know what decided you to design the high treble like that and what engineering or acoustic principles led you to the splayed rib pattern. The long sweeping cut-off allows to shorten up the longest ribs adding stiffness and and positions the bridge more toward the center of the entire rib structure. The way I understand things a spruce board is adequately stiff along the grain and the main purpose of the ribs is to bring the stiffness of the board across the grain to a similar degree of stiffness in order to achieve something like an orthotropic plate. Understood but in this case the idea was to support the bridge at angles perpendicular to it as in...thats where the load is, so lets support it first. 1. Your longer ribs perform this function but the further you get towards the treble the more the ribs are reinforcing the stiffness of the board along the grain, where it is not needed while supplying less and less stiffness across the grain, where it is needed. In order to increase the stiffness to a determined degree at the treble end of the board you are bound therefore to use a heavier rib than would be needed if the ribs were at a right angle to the grain, you are needlessly stiffening the board in the direction of the grain and you are adding more mass than yould otherwise be needed. I agree with you and the board is a bit stiff as evidenced by the voicing and hammer choice. More on that later. On a subsequent B I lightened up the rib dimensions for this reason and haven't heard back on that one yet. 2. Your masking of the edge of the board for the glue suggests that a full inch or more of the right hand end of the board is glued down to the inner rim, which brings the right-hand boundary of the sounding board say 20 mm closer to the end of the bridge than it would be if the inner rim were cut away to give a glue line 6 mm wide instead of the full width used for the rest of the perimeter. In other words a significant proportion of the board's area in this region is disabled when it could be used to advantage for the vibrations received from the highest strings. A second effect of this arrangement is that the board is stiffened, which brings me to... Not sure I follow. There is no fish just the board glued to the original width of the rim 3. To my eye, not only is your highest rib doing work in an unnecessary direction but it is supplying stiffness, together with the rim support, to the unsupported area of board above it, which in my design would have another rib. In other words, where you have one rib at 55 degrees to the grain, I would have two lesser ribs at a right angle to the grain. Good thoughts. After some discussions with David L. I've thought that keeping the ribs parallel with the grain angle instead of the bridge is sufficient support and also the board is stiff simply as it get smaller in the treble corner. The uppermost treble area of the board glue joint adds a good deal of stiffness. These ideas of mine are not some new-fangled approach I've dreamt up but can be seen applied in numerous pianos that have an excellent treble without even the aid of tuned partials or even capo bars -- how they might sound with these additions is quite a thrilling thought. You might answer the splaying question by saying you want the bars roughly at a right angle to the long bridge, in which case I would ask "Why?". Ok ,Why not? In this area, as you say, the grain angle runs quite nearly along the longish-most portion of the bridge so the ribs support both. What I perceive in sound is that it makes for a fabulous sounding tenor and bottom end. It really pumps air. The entire fanned rib display for me was an attempt to focus overall the tone and remove soundboard resonances which I define as weaknesses from note to note especially in the treble. The Treble is fantastic. No weak notes to my ears. so, This was surely accomplished. Could it be improved on? I think so in terms of making it a less stiff design in the treble so that less stiff hammers were used. To answer Jim Is question about voicing. I have an early version of the Weickert felt hammers in the piano. and..Yes, I sampled several hammers in the piano before I committed to the entire set. This is when I got excited! The sound was fantastic from the git go. Though the bass was to soft. Some of these early version Weickert felt sheets were quite stiff versions except the bass. Ray & I gave feedback to Jack and he improved the production and solved the bass end issues. The trebles were really dense and stiff and yet needles would go all the way in with beautiful resistance but a velvety compliance. From the moment these went on the tenor trebles came alive. Great sustain. Lots of pop. Roger Jolly spent some time with me demonstrating his single no.2 needle inserted 3 times up the cup line or in the middle of the hammer. This opened up the tonal spectrum. Over time I brought the bass up with weak 8 to 1 solutions. some in the low tenor and a little in the top octaves. One 15 minute session with needles in octave 4,5,6 and this is where the voicing is today. Dale As ever, the Devil's advocate! -- JD -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100720/1ea22f70/attachment.htm>
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