> From: JIMRPT@aol.com > Date: Mon, 16 Jun 1997 08:44:01 -0400 (EDT) > To: pianotech@ptg.org > Subject: Re: Soundboards/stress, questions > Reply-to: pianotech@ptg.org If the downpressure of the strings is 1.5 to 3.0 lbs wouldn't it be easy to lift up the strings with a string hook at the bridge? In my experience it isn't so easy...maybe the combination of the linear tension (such a beast?) and the downpressure is what I'm feeling. > Richard; > In a message dated 6/15/97 11:42:11 PM, you wrote: > > <<The load or pressure on the sb from the strings, I was told amounted > to a small elephant standing on it. Another source said 1,400 lbs. > (either a small elephand or a large cow) Would like to find the > formula to compute this.>> > > List, correct me if I'm wrong but isn't the typical pressure or 'down' > bearing on > the bridge from any individual string in the 1.5 to 3 lb range? Tension on > the plate is a different factor, related to 'down' pressure but not dependent > on it. > Plate tension can be determined by numer of pins(strings) X scale design > tension. > For example 200 strings X 180 lbs = 36,000 lbs, or 18 tons, of tension on the > plate /rim structure. > > Richard if the above is true than one formula to determine 'down weight' > would be > Number of strings crossing bridge X lbs pressure=down pressure > S (P) = DP > So in a typical piano, such as a Baldwin Mod. 'A', which has 206 pins and > therefore 206 times a string crosses the bridge, and using 2 lbs as the 'down > weight/pressure', the formula would be: > 206 (2)= 412 lbs > > Of course the down pressure and soundboard reach a state of equilibrium at > some point and there is where the true 'working' pressure should be measured. > Because of the ever increasing pressure applied to the board as the strings > are pulled to pitch the 'down' pressure changes as more and more strings are > pulled to pitch. This is just 'one' reason why it takes so many tunings to > establish a solid tuning on a new string or a new set of strings. > The effects of the 'down' pressure are accumulative and dependent on many > things most notably correct bridge height and plate setting. > So richard while a working down weight of 2 lbs might be correct on a > working sample, if measured while all other strings are in place, if you were > to reduce tension on all surrounding strings, before you measured the sample, > you find find a much, much higher 'down' weight. > > Due to changing characteristics, string length, string weight, etc. there > may be very few strings at 180 lbs of tension in a 180 lb scale. the spread > of tensions, as actually measured, would represent the typical "Bell Curve" > > Of course Richard my initial premise could be wrong. :-) > Jim Bryant (FL) > > > > ilvey Pacifica, CA ilvey@a.crl.com
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