Seasonal pitch change:

[Andrew and Rebeca Anderson]

Les,
I'd have tended to agree but the pattern repeats in all different 
types of pianos and in the same way for different people.  I think 
there is a smoking gun here.

Andrew

At 10:00 PM 3/7/2007, you wrote:
>Do people notice tiny discrepencies of lever pressure on tuning 
>pins?  We never can get all of them perfect. My suspicion is that 
>some of the unison problem is simply the fact we are never perfect 
>tuners, and as the piano "flexes", when it settles back those 
>discrepencies "come to the surface".......  There are so many 
>factors at work in tuning 3 strings together..... It's a miracle, to 
>me, anything stays.
>les bartlett
>
>
>----------
>From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] 
>On Behalf Of Andrew and Rebeca Anderson
>Sent: Wednesday, March 07, 2007 8:11 PM
>To: Pianotech List
>Subject: Re: Seasonal pitch change:
>
>I've been suspicious of soundboard deflection being entirely 
>responsible too, for different reasons.  Thanks to Ric we know we 
>need to look elsewhere.  I've also noticed a pattern to seasonal 
>pitch changes that involves the unisons, especially the three string 
>unisons.  It usually don't go out entirely the same way.  Sometimes 
>in opposite directions.  Think about it.  There's not a whole lot of 
>board and rib to push up or sag down, but there is a lot of board in 
>the horizontal positions.  I wonder how much bridge movement back 
>and forth we get with hydration and dehydration?  By the way, the 
>pattern is the same on uprights too.
>
>Andrew Anderson
>
>At 06:26 PM 3/7/2007, you wrote:
>>So has anyone measured plate expansion and contraction with 
>>temperature changes? Wouldn't that be the most likely suspect given 
>>this newfound innocence of the soundboard?
>>
>>Jason
>>
>>On 3/7/07, RicB <<mailto:ricb at pianostemmer.no>ricb at pianostemmer.no> wrote:
>>Hi List
>>I see I sent the wrong post, a copy of one earlier sent. Please excuse.
>>What I meant to write was the following.
>>
>>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.
>>Given the following string lengths, all with identical back lengths
>>(50mm), and lengths from front termination to tuning pins (200mm) (to
>>make the example simple) and assuming a 1 mm string deflection as the
>>starting point for all strings (also for simplicity) and calculating for
>>a roughly 50 cent pitch rise we get:
>>A string length of :
>>1400 mm needs 6 mm additional deflection which results in about 22 lbs
>>of downbearing.
>>1000 mm needs 5 mm additional deflection -->19 lbs downbearing
>>800 mm needs 4,5 mm additional deflection --> 18lbs downbearing
>>500 mm needs 3,5 mm additional deflection --> 15 lbs downbearing
>>250 mm needs 2,5 mm additional deflection --> 13 lbs downbearing.
>>100 mm needs 1,75 mm additional deflection --> 13 lbs downbearing
>>50 mm needs 1,2 mm additional deflection --> 13 lbs downbearing.
>>As you can see neither the amount of deflection needed to exact the
>>actual 50 pitch rise to begin with, nor the resulting downbearing
>>figures are within reason... which leaves one no choice but to admit
>>that something else is primarily responsible for seasonal pitch change.
>>Its also good to note that if we are starting with a 1 mm deflection to
>>begin with.. which btw yeilds reasonable enough string deflection
>>angles, then the absolute most downward pitch change possible is when
>>the panel flattens out and bearing becomes 0.  In this case the same
>>string lengths yeild :
>>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.
>>Tension change, and hence pitch change can come from an altering of the
>>relative positions of end points to each other... i.e. hitch pin and
>>tuning pin.  Pitch change can also happen without tension change if the
>>speaking length is somehow altered.  Seems to me that ruling out
>>vertical deflection... one has to look to these to general conditions
>>for the explaination.
>>Cheers
>>RicB
>>
>>
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>>
>>--
>>=cell 425 830 1561=
>
>
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