<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Soundboard stiffening</title></head><body> <blockquote type="cite" cite><br> <blockquote><font face="Times New Roman" color="#000040">   Phil writes</font></blockquote> <blockquote><font face="Arial"><br></font></blockquote> <blockquote><font face="Arial">      I keep reading posts by various people stating that the</font></blockquote> <blockquote><font face="Arial">soundboard gets 'stiffer' as downbearing is applied....</font></blockquote> <blockquote><br></blockquote> </blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040"><b>>> I believe it was getting stiffer but remember we're talking about a light weight system with limited ability to carry loads so great as to crush them altogether.</b></font><br> <blockquote><font face="Arial">It was<br> reaching a state of equilibrium for the applied load based on the<br> stiffness of the system.  That doesn't mean it was getting 'stiffer'.<br>       There is a difference between preload and stiffness. </font><br> </blockquote> </blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040">>>I'm honestly not sure about that. It seems like to me it's both.</font></blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040">  Was Ron Os demonstation on a board glued to the case liner? For the board will certainly react differently if the test is out of the piano with out the edges glued down</font></blockquote> <div><br> It was not glued to a rim.  But it was clamped so that the edges could not move out.  It should be in the archives.<br> </div> <blockquote type="cite" cite><br> <blockquote><font face="Arial">As you<br> apply more downbearing load to the board then the preload (or<br> prestress if you prefer) will increase.  It's not hard to believe<br> that this could have some affect on the vibrational characteristics<br> of the board and experience tells us that it does.  Putting<br> downbearing on the board usually seems to have a beneficial effect.</font><br> </blockquote> </blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040">>> And too much makes for a stingy sound especially in the treble</font></blockquote> <div><br></div> <div>Yes.  Good point.  If it was just about increasing stiffness while not increasing mass, then it would seem that one wouldn't so quickly reach an upper limit.</div> <div><br></div> <blockquote type="cite" cite><br> <blockquote><font face="Arial"><br></font></blockquote> <blockquote><font face="Arial">     Stiffness is a relationship between load and deflection....</font></blockquote> <blockquote><br></blockquote> </blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040"> <b> </b></font><font face="Times New Roman" color="#000040"><b> This is exactly what a board is doing when it is being compressed up to a point & then it will fail just as the beam will.</b></font><br> <blockquote><font face="Arial">  I see no reason why a ribbed panel would</font></blockquote> <blockquote><font face="Arial">behave in this way...</font></blockquote> <blockquote><br></blockquote> </blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040"><b>>>The way I look at it is that putting boards under some modest amount of strain via compression or tension for that matter makes the board more reactive and tonally efficient because of the impeding effect, which moves air & thet's why soundboards are built this way. If it wasn't Ron O would be building a flat board.</b></font></blockquote> <div><br></div> <div>This gets back to one of my original questions.  Is it increasing stiffness that matters or stress (or strain as you put it) in the board?  Or something else altogether?</div> <div><br></div> <blockquote type="cite" cite><br> <blockquote><font face="Arial">If the crowned board is not getting stiffer as it<br> deflects down, then a flat board would be just as stiff as a crowned<br> board.  So, the reason for the crown would not be 'stiffness'.</font><br> </blockquote> </blockquote> <blockquote type="cite" cite><font face="Times New Roman" color="#000040">Phil</font></blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040"><b>>> But I think it is getting stiffer.</b></font></blockquote> <blockquote type="cite" cite><font face="Times New Roman" size="+1" color="#000040"><b>     Dale</b></font></blockquote> <div><br></div> <div>Well, you've done it many times, so your opinion means more than mine.  But if it is getting stiffer I'd like to know why.  Have you tried the same thing with an initially flat board?  Did it get stiffer as you wedged it down?  Was the increase in stiffness comparable to a crowned board?  If so, then why bother with the crown?  I think it's time for some measurements.  I guess I'm going to have to do some deflection vs. load measurements on a few pianos.  Another thing to put on the list of things to do.</div> <div><br></div> <div>Phil</div> </body> </html>