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

[Marcel Carey]

Hi Ric,

Yes, but... The most change happens in the tenor (longer stings with
lower tension generally) and above the treble break. When it gets to the
top octave, I would be inclined to think that the pitch doesn't move
that much except there always seems to be a row of pins that is affected
more. Sometimes I can really clean the treble just by doing unisons by
moving the front row of pins. So I'm still thinking this has to do with
soundboard, bridge, rim and pinblock assembly.

But as you may know, 2¢ (canadian) is not worth that much anymore. ;-)

Marcel Carey,
Sherbrooke, QC

> -----Message d'origine-----
> De : pianotech-bounces at ptg.org 
> [mailto:pianotech-bounces at ptg.org] De la part de RicB
> Envoyé : 1 mars 2007 17:48
> À : pianotech at ptg.org
> Objet : Seasonal pitch change: was -- Long term pitch drop, 
> was: Type O
> 
> 
> 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
> 
> 
> 
>