<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: tuning instability/plate struts</title></head><body> <div><font face="Geneva" size="-1" color="#000000">Tom,</font></div> <div><font face="Geneva" size="-1" color="#000000"><br></font></div> <div><font face="Geneva" size="-1" color="#000000">At 3:17 PM -0500 17/1/04, Tom Sivak wrote:</font></div> <div><font face="Geneva" size="-1" color="#000000"><br></font></div> <blockquote type="cite" cite><font face="Geneva" size="-1" color="#000000">Certainly I think we can agree that strings near the plate struts go out of tune more than those in the center of their sections.</font></blockquote> <div><br></div> <div>Often, and primarily because the string tension<font color="#0000FF"> (when expressed as a percentage of breaking strain)</font> goes low on the treble side of the bar and high on the bass side.</div> <div><br></div> <blockquote type="cite" cite><font face="Geneva" size="-1" color="#000000">  And when it comes to the tenor break, I think I can understand why this would happen.  The treble bridge ends there, often the stringing scale goes to copper-wound strings for the last couple of unisons</font></blockquote> <div><br></div> <div>Because the designer has run the scale too low, for the particular length of piano, before crossing to the bass bridge. This results in a low tension problem, which the manufacture sometimes attempts to address by using copper wrapped bichords for the most disastrous offenders.</div> <div><br></div> <blockquote type="cite" cite><font face="Geneva" size="-1" color="#000000"> and I imagine the tension of those strings differs from their steel neighbors.</font></blockquote> <div><br></div> <div>Certainly, but if the scale had been thought through properly at the design stage, the tuning problem wouldn't exist and the wrapped bichords would be unnecessary.</div> <div><br></div> <blockquote type="cite" cite><font face="Geneva" size="-1" color="#000000">  And right on the other side of the break, the strings are strung across in another direction; all of those things could probably contribute to instability, although I say this not out of knowledge of the situation, but just looking at it in a logical (but basically uninformed) way.</font></blockquote> <div><br></div> <div>Very often there is a huge variation in the percentage of breaking strain at the bass/treble break. For example, the chart below shows the percentage of breaking strain for a Steinway model C grand piano.</div> <div align="center"><img src="cid:a06002000bc2f5a17be4a@[61.8.27.70].1.0"></div> <div><br></div> <blockquote><i>(I could have chosen the Yamaha U1H scale - amongst many others - to illustrate this trend, but I chose this model to show that the problem is commonplace, even for high end instruments)</i></blockquote> <blockquote><br></blockquote> <div>Note that the % brk has dropped down to the mid 20s in the treble before crossing to a bass bichords in the high forties. This is a consequence of setting the break at the same place as for the concert grand. While E20/F21 will work with a speaking length of 183 cm for F21 on a concert piano, you cannot accommodate a respectable plain wire F21 speaking length into a 225 cm piano. Notice also the % brk glitch between notes 49 and 55. This occurs at the bar between the last agraffe section and the first capo section in this piano. This % brk variation is the cause of the tuning stability problem at the bar.</div> <div><br></div> <blockquote type="cite" cite><font face="Geneva" size="-1" color="#000000">But why does this also happen in the treble break?  Often there's one continuous bridge.  Steel strings on both sides.  All strung parallel.  And yet notes on either side of this break generally go out quicker and farther.</font><br> <font face="Geneva" size="-1" color="#000000"></font></blockquote> <blockquote type="cite" cite><font face="Geneva" size="-1" color="#000000">Why should those strings be less stable? </font></blockquote> <div><font face="Geneva" size="-1" color="#000000"><br></font></div> <div>When recapping bridges, we analyse the % brk across the breaks, adjusting the speaking lengths to achieve a uniform percentage of breaking strain. Often it will be necessary to build a slight 'dog leg' into the bridge cap to accommodate the adjusted speaking lengths<font color="#0000FF"> (but the dog leg must not extend down to the bridge/panel contact)</font>. We have been making these changes to pianos since 1990 and the improvement in tuning stability is noticeable.</div> <div><br></div> <div>At the lower end of the treble bridge a short tenor bridge scaled with bichord covered strings is a good solution<font color="#0000FF"> (apart from the obvious one of designing the piano properly in the first instance)</font>. Typically, the first note on the tenor bridge<font color="#0000FF"> (when moving down from the treble)</font> can be shortened in speaking length 12 - 14% relative to the speaking length immediately above it, with a core wire two 1/2 gauges smaller and wrapped with a 0.2 mm copper cover.</div> <div><br></div> <div>Unfortunately, after shortening the speaking lengths on a new tenor bridge to fix a scaling disaster, you will have created a strike ratio problem. The shortened notes will now have a lower strike ratio. If the plate permits, you could relocate the agraffes to correct it, or you could shorten the hammer position on the shank. However, shortening the hammers will lower the hammer/key leverage ratio.</div> <div><br></div> <div>So, relative to the ease of addressing design issues at the time of manufacture, rectifying it later is a lot of trouble. If only manufactures would commit a little more effort to design, and a little less to marketing spin. Such is the problem that I suspect worthy design might go unnoticed amongst the general background noise of marketing hype.</div> <div><br></div> <div>Best,</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:info@overspianos.com.au<br> _______________________</font></div> </body> </html>