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

[Thomas Cole]

Has anyone noticed how semilog progression bridge pianos are more 
sensitive to seasonal pitch change than hockey stick bridge pianos, or 
plain-capped bridges compared with laminated bridges? *Elongation* of 
the bridge in the tenor area might affect tuning more than say upper 
treble due to angle of the bridge and space between notes.

Tom Cole

RicB wrote:

> 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
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