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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.<br><br>
Andrew Anderson<br><br>
At 06:26 PM 3/7/2007, you wrote:<br>
<blockquote type=cite class=cite cite="">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?
<br><br>
Jason<br><br>
On 3/7/07, <b>RicB</b>
<<a href="mailto:ricb@pianostemmer.no">ricb@pianostemmer.no</a>>
wrote:<br>
<dl>
<dd>Hi List<br><br>
<dd>I see I sent the wrong post, a copy of one earlier sent. Please
excuse.<br>
<dd>What I meant to write was the following.<br><br>
<br>
<dd>I've been running some numbers and thinking a bit about this
traditional<br>
<dd>idea that vertical deflection of the strings is the main cause of
pitch<br>
<dd>change and thought some of you might find this interesting.<br><br>
<dd>Given the following string lengths, all with identical back
lengths<br>
<dd>(50mm), and lengths from front termination to tuning pins (200mm) (to
<br>
<dd>make the example simple) and assuming a 1 mm string deflection as
the<br>
<dd>starting point for all strings (also for simplicity) and calculating
for<br>
<dd>a roughly 50 cent pitch rise we get:<br><br>
<dd>A string length of :<br><br>
<dd>1400 mm needs 6 mm additional deflection which results in about 22
lbs<br>
<dd>of downbearing.<br>
<dd>1000 mm needs 5 mm additional deflection -->19 lbs
downbearing<br>
<dd>800 mm needs 4,5 mm additional deflection --> 18lbs downbearing
<br>
<dd>500 mm needs 3,5 mm additional deflection --> 15 lbs
downbearing<br>
<dd>250 mm needs 2,5 mm additional deflection --> 13 lbs
downbearing.<br>
<dd>100 mm needs 1,75 mm additional deflection --> 13 lbs
downbearing<br>
<dd>50 mm needs 1,2 mm additional deflection --> 13 lbs downbearing.
<br><br>
<dd>As you can see neither the amount of deflection needed to exact
the<br>
<dd>actual 50 pitch rise to begin with, nor the resulting
downbearing<br>
<dd>figures are within reason... which leaves one no choice but to
admit<br>
<dd>that something else is primarily responsible for seasonal pitch
change. <br><br>
<dd>Its also good to note that if we are starting with a 1 mm deflection
to<br>
<dd>begin with.. which btw yeilds reasonable enough string
deflection<br>
<dd>angles, then the absolute most downward pitch change possible is when
<br>
<dd>the panel flattens out and bearing becomes 0. In this case the
same<br>
<dd>string lengths yeild :<br><br>
<dd>1400 mm length --> -1 cent<br>
<dd>1000 mm length --> -1,4 cent<br>
<dd>800 mm length --> -1,7 cent<br>
<dd>500 mm length --> -2,4 cent <br>
<dd>250 mm length --> -4 cent<br>
<dd>100 mm length --> -7 cent<br>
<dd>50 mm length --> -10 cent<br><br>
<dd>These examples are simply illustrative of the kinds of things
that<br>
<dd>actually has to happen if the soundboard rise and fall is to account
for <br>
<dd>most of the pitch change. I apply all the resulting change on
the<br>
<dd>speaking length itself and do not account for any friction.
This is a<br>
<dd>best case scenario. In reality the string will disperse some of
any<br>
<dd>change in tension caused by a change in vertical deflection...
lessening <br>
<dd>the frequency change and resulting downbearing... but necessitating
even<br>
<dd>more vertical change for any give change in pitch.<br><br>
<dd>I can not help but conclude... looking closer at the
consequences....<br>
<dd>that vertical rise and fall of the soundboard simply doesnt have much
to <br>
<dd>do with the seasonal pitch change at all.<br><br>
<dd>Tension change, and hence pitch change can come from an altering of
the<br>
<dd>relative positions of end points to each other... i.e. hitch pin
and<br>
<dd>tuning pin. Pitch change can also happen without tension change
if the <br>
<dd>speaking length is somehow altered. Seems to me that ruling
out<br>
<dd>vertical deflection... one has to look to these to general
conditions<br>
<dd>for the explaination.<br><br>
<dd>Cheers<br>
<dd>RicB<br><br>
<br><br>
<br><br>
<br><br>
<br><br>
</dl><br><br>
<br>
-- <br>
=cell 425 830 1561= </blockquote></body>
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