<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; = charset=us-ascii"> <META content="MSHTML 5.50.4522.1800" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV>Thank you very much for your response Dale. Some good info here. I = will read those articles.</DIV> <DIV> </DIV> <DIV>Terry Farrell  </DIV> <BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black">From: <A title=Erwinspiano@AOL.COM href="mailto:Erwinspiano@AOL.COM">Erwinspiano@AOL.COM</A> </DIV> <DIV style="FONT: 10pt arial">To: <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">pianotech@ptg.org</A> ; <A title=davehugh@msn.com = href="mailto:davehugh@msn.com">davehugh@msn.com</A> </DIV> <DIV style="FONT: 10pt arial">Sent: Sunday, January 20, 2002 = 8:47 PM</DIV> <DIV style="FONT: 10pt arial">Subject: Re: Soundboard Pre-Stressing/Downbearing, was: Baldwin accu-hitch pins</DIV> <DIV> </DIV>In a message dated 1/20/2002 6:41:51 AM Pacific = Standard Time, <A = href="mailto:mfarrel2@tampabay.rr.com">mfarrel2@tampabay.rr.com</A> writes: <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">  Terry</BLOCKQUOTE>   >>>Welcome to the insomnia club. Considering all the variables in the always in flux soundboard system = I've always thought that setting bearing to the degree you are speaking = ofis a bit like making a jello foundation for a house. Just when you thought you = had the right consistency poof it wiggled and the house fell over.   = Well it's not quite as bad as all that <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE"> I have always been curious about the soundboard pre-stressing method of targeting downbearing, but when I ask how = much to push the soundboard down, I get answers like: "enough", "not too = much" and the like. The idea of getting a feel for how much the soundboard = will deflect under load I should think would help target proper = downbearing Now I see here we are using some numbers. This is a good thing. You say = David Hughes deflects the board 3 mm at the center strut. You state that = you drive wedges under each strut. How much do you deflect the board at each strut?</BLOCKQUOTE>   >>>>The short answer is after = driving the maple wedges in, readings of deflection will be appox.3 to 3.5 at = the central strut about 2 ish on the next treble strut and 1 to.05 on the = top. The lowest tenor strut can be forced lower than is needed and should not = be over driven. It's value will be in the 2 mm range. But hey if you don't = want to take my word for it e- mail Dave hughes at  davehugh@msn.com and = ask him.        <FO= NT lang=0 style="BACKGROUND-COLOR: #ffffff" face=Arial = color=#000000 size=2 FAMILY="SANSSERIF"> Terry, save some time and read  John = Hartman 'effects of downbearing = on tone' aug,sept oct nov. 1996. Very good reference material. The last article = will give you some numbers that I can see a person like you is ready to = digest. I have posted a description of this in the last year on this = list. <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE"> Now the other question I have is that I assume the = reason one would pre-stress the soundboard is to incorporate into your work = how much the soundboard will deflect under load. </BLOCKQUOTE> >>>>>>..  Yes an approximation    But if you deflect the soundboard = 3mm or whatever, wherever, for any given <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">soundboard, what does that do for you (i.e., you are = pushing a stiff board 3mm down, and you would be pushing a highly flexible = board 3mm down - under strung conditions, obviously the flexible board would = deflect more under final strung downbearing)?</BLOCKQUOTE> .>>>>>> Ist = question. Your making it stiffer and changing the = impedance .>>>>>Yes but for the sake of discussion lets stick to newly crowned boards. The = same principles can be modified for other situations. Rib crowned boards = with either sugar pine or spruce ribs and duplicated to original rib = heightswill result i a stiffer board than the old compression crowned boards and = the amount they compress is fairly predictable.   >>>>>>>> Remember jello? It moves. So does a = new unstrung soundboard. Up And down with moisture content. So at what = point in the moisture content cycle are you going to set your bridge heights/downbearing. More insomnia material.         You could simply calculate the needed angles = without pre-stressing the board. <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">Now if you could pre-stress the board with downward = pressure approximately equal to that of the final string downbearing in the = various regions of the scale, then we would be truly simulating the = soundboard's reaction to the strung-up load and accurately calculate our desired = string downbearing angles, etc. Of course to do this we would need some = sort of pressure gauge/device. >> Terry I know Steinway doesn't = carry much weight with you but they've done it this way for a hundred = fifty years but so has mason and others</BLOCKQUOTE> >>>See Bob Hofs article on this last = year he uses go bars off the Ceiling. The down side to that is I can't feel what go = bars are doing  in the same way as I can with my fist.   = >> With the maple wedges I insert them between the struts with the left hand = as I  pound with my right fist on the bridge top. As the board sinks = to appox. 3 mm it gets so stiff it feels like your pounding on a gym = floor. Or you pound till it feels real stiff It's an aquired feel that's not = difficult to get the hang of. Repeat at each strut. <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">What about a rig similar to a pneumatic rib clamp. Just = use the half with the fire hose. Clamp it to the rim above the bridge, = inflate, and there you go with measurable pressure applied all along the long = bridge in much the same manner as downbearing would be once the piano is = strung. You could also use four segments of fire hose to apply appropriate = variable pressure to each of the four sections (and one on the bass if you = want to do that). The result would be a board stressed in very much the same = manner as it would be after stringing. Then you could set your downbearing = exactly where you want it, armed with the knowledge of exactly (or there = abouts) how much the soundboard will deflect!</BLOCKQUOTE>    >>>>Dave Love was right, = no access to the bridge. <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE"> So now, readers..........you are thinking one of two = things: Either Terry Farrell needs to get his head screw on properly, i.e. = it's a dumb idea, or it sounds like a great idea, now go try it Terry and = write us back. So what do you think?</BLOCKQUOTE>    >>>Your doing some good = thinking. no worrys you're on your way <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">Maybe it is the case that with a given soundboard = construction, the boards are consistent enough to yield predictable result when pre-stressed 3mm or whatever. Is this the case, and thus would yield = a more accurate pre-stressing a waste of time?</BLOCKQUOTE>     >>>>This = what  I'm gettin at <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">I guess I'm just thinking and probing for information. = Any input would be appreciated. I realize the thing to do is put in a couple = dozen boards, try some different methods, and see what = happens.</BLOCKQUOTE> >>> This helps a lot. = Of course  don't forget the fun factor. I hope this is helpful = verses annoying. But boy oh boy, that = will be years, and I would fear, some tears. I'm just trying to <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE"> <DIV>arm myself with as much info a possible before I screw up too = darn many pianos. Terry Farrell</DIV> <DIV> </DIV></BLOCKQUOTE> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE">SNIP <DIV> </DIV></BLOCKQUOTE></BLOCKQUOTE></= BODY></HTML>