Seasonal pitch change:

[Don]

Hi Ric,

Most interesting figures. I've not believed soundboard moving up and down
had much to do with pitch corrections for some years.

What I *do not* understand is *why* damppchasers work to ameliorate
seasonal pitch change. Clearly they don't have much effect on metal. That
leaves the rim and the main frame as possibilities.

At 01:12 AM 3/8/2007 +0100, you wrote:
>Hi List
>
>I've been running some numbers and thinking a bit about this traditional 
>idea that vertical deflection of the strings is the main cause of pitch 
>change and thought some of you might find this interesting.
>
>1400 mm length --> -1 cent
>1000 mm length --> -1,4 cent
>800 mm length --> -1,7 cent
>500 mm length --> -2,4 cent
>250 mm length --> -4 cent
>100 mm length --> -7 cent
>50 mm length --> -10 cent
>
>These examples are simply illustrative of the kinds of things that 
>actually has to happen if the soundboard rise and fall is to account for 
>most of the pitch change.  I apply all the resulting change on the 
>speaking length itself and do not account for any friction.  This is a 
>best case scenario. In reality the string will disperse some of any 
>change in tension caused by a change in vertical deflection... lessening 
>the frequency change and resulting downbearing... but necessitating even 
>more vertical change for any give change in pitch.
>
>I can not help but conclude... looking closer at the consequences.... 
>that vertical rise and fall of the soundboard simply doesnt have much to 
>do with the seasonal pitch change at all.
>
>Cheers
>RicB
Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T.
Non calor sed umor est qui nobis incommodat

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