[pianotech] Pitch Change (was: Grey market pianos, seasoned pianos, etc.)

[Gerald Groot]

I did read that William, thank you.  After reading more of it as well, it
appears to me that there is much more speculation than positive proof either
way from either Ric or John.  

 

I visited with Dr. Yat Lam Hong all afternoon today.  He is a man FULL of
information and is most willing to share it.  How he manages to retain it
all is beyond me.  I wish I had that kind of memory.  For those of you that
do not know Yat Lam, he is an extremely knowledgeable RPT.  

 

I asked Yat Lam Hong his philosophy on what he thought was the main cause of
why pianos go out of tune so drastically from seasonal changes and his
immediate reply was "humidity."  He went on to say that "humidity causes
swelling and contraction of the sounding board sending pitch up and down.."
A pure and simple answer.   I asked him about the rim being a factor.
"Possibly some, but no, not much."  Adding:  "It would be a very small
factor as would the sounding board near the rim because it is glued down
there.  The bass section changes tuning and pitch also but not nearly as
much as the tenor section.  One reason is because it is closer to the edge
of the piano.  Whereas the tenor section of the pianos bridge runs down the
middle of the sounding board where it swells and contracts the most."  

 

We both agreed that there some other factors that do come into play.  Some
of them have been mentioned here such as heat or lighting.  We both think
however, that the major contributing factor is the sounding board swelling
and contracting.  So, I stand firmly by what I was taught.  We had other
things to do so we dropped it at that.  

 

Jer

 

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of William Monroe
Sent: Saturday, April 03, 2010 1:59 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Pitch Change (was: Grey market pianos, seasoned
pianos, etc.)

 

Hi Gerald, List,

Having sifted through the archives.........  ;-]

OK, so my memory did serve.  Here's an excerpt from Ric Brekne's posting of
the math that shows resultant pitch changes due to rise & fall of a
soundboard.  This shows minimal effect on pitch due to soundboard
deflection.  Here's a link to the archives as well with the thread, "
Soundboard Deflection and Pitch Change / was Downbearing."

https://www.moypiano.com/ptg/pianotech.php/2006-August/thread.html#194422


 
William R. Monroe














Ric wrote:





.............Let me illustrate..given the following, and by all means check
my 


figurings... (for the moment disregard the width of the bridge and deal 


in simple triangle trig)












- an undeflected string tension of 160 lbs.


- string diameter of 0,8 mm.


- front length of 50 mm.


- back length of 25 mm.





This yields a front length frequency of roughly 4248.88 Hz.  f = SQRT((T 






* 398 *10^6)/(L^2d^2))








If you then deflect this string 1 mm upwards you get a string deflection 


angle of a whopping 3.46 ¤,  a downwards force of 9.59 lbs, and a 


frequency of 4248.98 hz. Thats only a change of 0.106 hz.... at note 88 









or there abouts.  Even a 2 mm deflection would'nt increase the frequency 


of the string more then 0.42 hz and that would at the same time cause a 


string deflection angle of 6.87 ¤ !! and a downbearing force of just 









over 19 lbs... for just one string ! You'd be quickly over 3000 lbs of 


total downbearing force on the soundboard...





If these figures are correct... then clearly soundboard deflection can 


nearly be ignored when it comes to pitch changes. 

 

On Sat, Apr 3, 2010 at 9:55 AM, Ron Nossaman <rnossaman at cox.net> wrote:

Gerald Groot wrote:

I have read what has already been written in this thread, currently.  Ron,
I'm not going to sift through the archives.  The dissusion has been and
still is being presented now.  I'm merely adding to it as you are giving my
current thoughts on the matter again, as you are.      
Have YOU had the time to do all of these measurements yourself?  If so, I
don't know how you managed to find it let alone have the patience for it.  I
haven't nor do I have the desire to do so.  Taking measurements is not the
only proof available.  When does logic and common sense ever come into play
here?  

 

It comes into play immediately when you find how much a soundboard has to
move to produce the required tension changes. Yes, I've taken a whole lot of
time trying to learn how things actually work, rather than assuming that
what I was taught was correct. It used to be common sense that horse hairs
in the rain barrel turned into worms. I take the time because I'm interested
in learning something real.

Ron N

 

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