[CAUT] pre-stretching new string? Ed

[Richard Brekne]

Hi Ed

Sorry if this got too intense for you, and for whomever else for that 
matter.

The contribution to all this I have attempted to make is that there is a 
simple way of looking at certain requirements that are placed on the 
string when attempting to make assumptions about any contributing factor 
relating to climate pitch change. Regardless of breaking point 
percentages and the rest of it.  If changes of segment lengths are to 
account for any significant amount of pitch change for any given 
string... then said string and that what is responsible for changing its 
length must be factually able in real world conditions to change thus.  
That indeed is the entire basis for Ron N's claim that the soundboard 
moving up and down can
not account for any significant amount of pitch change.  Which I agree 
with.

The spread sheet I supplied quite simply describes what happens to the 
tension, length, pitch and downbearing force of any given string for any 
given change in deflection at the speaking length temination. It doesnt 
take into consideration friction at the various segment points... but 
rather spreads that evenly across both front and back length. Be that as 
it may, it very adequately describes certain conditions that very 
closely to must be met. If observered pitch changes can not match the 
kind of reasons we attribute for length changes... then something else 
must be at work.

Much has been made of the low tension strings on the tenor end of the 
bridge.  Here is a natural born fact. If you have a 1400 mm long string, 
with a 100 mm long back length, 1,2 mm Ø and set at 125 lbs tension and 
undeflected vertically... it will have a pitch of 89,42 hz. A 4.33 
vertical deflection would be needed for a 0.1 mm increase in overall 
string length. This increase would increase tension on the string to 
128.064 lbs.  The combined increase in tension, and increase in length 
results in a pitch change of 1,21 hz. or a change of roughly 23 cents. 
Such a vertical deflection also carries with it a 5.9 lb per string 
downbearing force on the bridge.

I personally am skeptical to a 4.33 mm change in vertical deflection by 
the soundboard / bridge to begin with, especially at the area of the low 
tenor.  Secondly with that much downbearing per string I would think the 
board wouldnt be able to exert enough upwards pressure even if it wanted 
too... but perhaps I am wrong. Much more interesting is the idea that 
the bridge surface rises much smaller increments that cause an increase 
in string length by virtue of the increase in string offset angle 
through the bridge pins.  In anycase... one needs to accomplish a 0.1 mm 
increase in overall string length to increase tension enough to account 
for a 23 cent change for this string.  Just what cause(s) is (are) most 
likely is whats up for discussion.

And in my book... it is a fun one, and an enlightening one.  Tho I am 
not sure just how much practical daily daily good it does me beyond 
increasing my basic knowledge base.  Certainly no reason for ruffled 
feathers or any other such reaction.

Cheers
RicB