Seasonal pitch change: was -- Long term pitch drop, was: Type O

[RicB]

Hi all

Got to thinking about this previous thread middle/early last month.  
Nossaman mentions as he has several times in the past a skepticism 
towards soundboard / bridge vertical rise/fall having anything to do 
with seasonal pitch change.  My own calculations confirm this... and 
these are backed up by folks who should have more then adequate 
education in physics. 

So... since it seems evident that vertical deflection of the string is 
not part of this picture.... perhaps to some significant degree string 
length is changing... and as a result tension is NOT changing... or not 
nearly as much as we take for granted.

Since the change in pitch is related to seasonal changes... ie relative 
humidity changes... we are talking movement in wood.  The width of the 
bridge is wood and can/will expand contract somewhat. Instead of the 
whole assembly pushing upwards more/less in response to climate 
change... perhaps the strain causes a slight rolling of the bridge.  
Breaks in the bridge would resist as there is no counter pressure by the 
strings.... and this resistance could account for some of the abrubt 
change in pitch change over the breaks. 

My point is that instead of looking in the direction of change in 
tension to explain things.... perhaps we should be looking at possible 
changes in speaking length segments. Wouldnt take much to make a big 
difference... especially in the top.  1 mm change in speaking length for 
a 50 mm string with no tension change is around 35 cents... and for a 
1400 mm length about 1.5 cents.

just some thoughts

Cheers
RicB