<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Soundboard crown</title></head><body> <blockquote type="cite" cite>At 10:07 PM +0300 11/8/03, Calin Tantareanu wrote:</blockquote> <blockquote type="cite" cite>. . . By the way, how do laminated soundboards behave when exposed to humidity?</blockquote> <blockquote type="cite" cite>Do they expand less than solid wood ones?</blockquote> <div><br></div> <div>If you dry a quarter cut solid panel down to around 6% it will shrink about 3 mm in 900<font color="#0000FF"> (this will depend on the closeness of the growth rings, tighter grain shrinks less and vice versa)</font>. If you repeat the procedure with a laminated panel<font color="#0000FF"> (with all laminates properly quarter cut and carefully joined as they should be also for a solid panel)</font> you will have trouble measuring any shrinkage.</div> <div><br></div> <div>So for CC brigade, laminated panels cannot be used. Mind you, there is still a small shrinkage with the laminated panels, since we are finding that our 7.5 mm thick laminated tests panels are pushing the crown up about 0.5 to 1.0 mm once they are normalised after gluing. I don't really want any rise from panel compression but I feel the need to dry the panel just a bit, to provide a small insurance for extremely dry conditions.</div> <div><br></div> <div>I have been doing sound board deflection tests for the past two weeks straight. Amongst my findings, I have found that the typical modern sound board is so grossly overloaded in the killer octave region that there is little hope of such under-engineered sound boards ever giving a respectable service before the dreaded 'set' sets in.</div> <div><br></div> <div>Try your own quick test with a sample to see what I mean. Our rib no. 11 on our 225 piano supports notes C52 to F#57, and has an active length of 580 mm. With just 1% of down bearing (which is quite moderate by current standards) this rib and panel strip will be subjected to a down force of 24.4 Kg. Build yourself a test rib of the contemporary-full-dimensioned sized of 25 X 25 mm (Steinway D mid board ribs), glue it to a 120 mm wide test panel and load it up on the bench with a 24 Kg test weight. You'll quickly realise why the typical piano's killer octave is well and truly dead before it arrives at the showroom. When you consider that most makers are using ribs smaller than 25 X 25 in the killer area, these will be subjected to even greater stresses. As an aside, I had occasion to take a look under a late Stuart concert piano a few weeks. The observed 20 X 21 mm rib dimensions would seem, in the light of this discussion, to be an unusual approach.</div> <div><br></div> <div>Yes, I am working on a solution to this engineering disaster for the very next sound board.</div> <div><br></div> <div>Best to all,</div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div><font size="-2" color="#000000"><br> </font><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<br> mailto:ron@overspianos.com.au<br>      _______________________</font></div> </body> </html>