<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: A tenor bridge conversion</title></head><body> <div>Hi André,</div> <div><br></div> <div>Nice to see you in print again.</div> <div><br></div> <blockquote type="cite" cite>I have a question :</blockquote> <blockquote type="cite" cite><br></blockquote> <blockquote type="cite" cite>You cut off the treble bridge in the tail. Did you do that because that last part of that treble bridge is so close to the rim?</blockquote> <div><br></div> <div>No, the proximity of the bridge to the rim in this case was actually OK (although the bass bridge is too far in from the rim as usual), it was the tension and stiffness of those large diameter wires at such a low tension which is the problem.</div> <div><br></div> <blockquote type="cite" cite>I worked on a brand new Bechstein C and I noticed that those first treble notes (nr 21 to appr. nr 30 sounded weird and were difficult to voice correctly, as usual).</blockquote> <div><br></div> <div>That's the problem (the first plain wire tri-chord is note E32 in the modified piano), they can't be voiced because the inharmonicity is way up, the Z is way down and the % break is way low. There is nothing that anybody could hope to achieve with voicing needles. The original scaling is an utter mess.</div> <div><br></div> <blockquote type="cite" cite>I also wonder what kind of string thickness you use on that new bridge you built. Do they get thicker in size because they are shorter?</blockquote> <div><br></div> <div>No they don't. On the standard piano they do but it isn't the right way to go (from my perspective). That is part of the problem. If the tension is dropping because of the hockey stick bridge, increasing the wire diameter will only make a bad situation worse.</div> <div><br></div> <div>We actually use thinner core wire with a wrap to achieve a balance between inharmonicity, Z and % brk. But such a redesign can't be achieved without also using a tenor bridge. There is a golden rule when crossing from plain tri-chord wire to wrap, there must be a reduction in speaking length of between 10 to 14 % for the first covered bi-chord note (tri-chord covers also should be confined only to history books). The ideal reduction in speaking length depends on the choice of core and wire wrap diameters. You can't re-configure the string sizes while keeping the hockey-sick end. I realise that a number of manufacturers do just that, but it doesn't work.</div> <div><br></div> <div>Here are some reduced size graphs of %brk, Z and Inharmonicity for both the original scale and the new tenor conversion.</div> <div><br></div> <div>Here is the original scale. % brk is the top graph, Z the middle, and I(4) the lower two.</div> <div><br></div> <div align="center"><img src="cid:a06240810c1daee758b0d@[192.168.0.6].1.0"></div> <div><br></div> <div>The tension drops to around 20% in the low bass as well. We revise the diameter of both core wire and the cover wrap in the bass also. Notice also that the inharmonicity turns and heads upwards before the long bridge crosses to the bass. This is typically what happens with hockey stick ends. Overall tension 16850 Kg.</div> <div><br></div> <div>And here is the tenor bridge conversion.</div> <div><br></div> <div align="center"><img src="cid:a06240810c1daee758b0d@[192.168.0.6].1.1"></div> <div align="center"><br></div> <div align="center"><br></div> <div>Overall tension 16785 Kg. While the tension per unison has risen considerably, there are less strings overall with the bi-chord tenor scale, so the overall tension is reduced slightly.</div> <div><br></div> <div>To answer Calin Tantareanu, he asked about the problem of strike point with the tenor. That's a good question Calin, and yes it does create a problem, because we've moved the bridge position and it will result in a strike ratio which is further out on the speaking length. Ideally, we should also shift the agraffes to keep the strike ratio correct, but in this case we'll reduce the hammer position along the shank about 5% to help offset the negative effect of the strike ratio change. It won't be ideal, but it won't have nearly as bad an effect as the original poor scaling had on the tone. We'll be able to do some voicing to help blend the tone. It won't be perfect, but nevertheless the net result will be a considerable overall improvement.</div> <div><br></div> <div>In the case of this piano, the client wasn't prepared to spend enough to allow us to move the agraffes as well. We're considering doing an S&S B next year by moving the agraffe line to keep the strike ratio correct. A model B with a tenor and moved agraffes is the ultimate fix for that piano.</div> <div><br></div> <div>The soundboard was stripped, sanded and refinished. The original bridge had nothing physically wrong with it. It was just a matter of scaling.</div> <div><br></div> <div>Feel free to forward my posts to the Bechstein Yahoogroup, but I'm not prepared to get into a major debate defending the work we do.</div> <div><br></div> <div>Hope it all makes sense.</div> <div><br></div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div><font face="Times New Roman" size="+1" color="#0000FF"><b>OVERS PIANOS - SYDNEY</b></font></div> <div><font color="#000000"><i>   </i></font><font color="#0000FF"><i>Grand Piano Manufacturers</i></font><font color="#000000"><br> _______________________</font></div> <div><font size="-2" color="#000000"><br> </font><font color="#000000">Web http://overspianos.com.au</font></div> <div><font color="#000000">mailto:ron@overspianos.com.au<br> _______________________</font></div> </body> </html>