Soundboards/stress, questions

[David ilvedson]

> 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