[pianotech] Soundboard deflection - Pitch raise

[Ron Nossaman]

David Nereson wrote:
> ----- Original Message ----- From: "Ron Nossaman" <rnossaman at cox.net>
> To: <pianotech at ptg.org>
> Sent: Tuesday, August 04, 2009 8:15 PM
> Subject: Re: [pianotech] Soundboard deflection - Pitch raise
> 
> 
> I'm confused, and having to re-learn almost everything I was taught 
> about humidity changes and how they affect or don't affect the tuning.

I had to. I don't know why you shouldn't  too. <G>

> This statement:
> 
>> Exactly. Just like soundboard rise and fall with humidity swings
> 
> says that the soundboard does rise and fall with humidity changes.  But 
> the rest of it:

It's BELIEVED that soundboard rise and fall with humidity 
swings is responsible for pianos going out of tune, just like 
it's BELIEVED that the soundboard deflecting is responsible 
for pitch drop during pitch raises. NEITHER is the case.


> says that those rises and falls don't affect tuning much.  Then what 
> DOES make the low tenor strings go 25 cents sharp during the summer, and 
> drop back down after the heat's been running for a couple weeks?

Once again, the low tension and low break% scaling in those 
low tenor notes makes them much more reactive to tension 
changes. We've discussed this a half dozen times on list just 
this year. Lots of reading in the archives.


>    On a related note (pun intended), a new customer just moved their 
> grand from Boston to Denver.  Typically pianos go way flat when moved to 
> dry Colorado from more humid places.  Are you going to say that's not 
> the soundboard falling?  

I've been saying it for some time. It's not the soundboard 
falling. String bearing angles, assuming there is any bearing 
through the middle of the scale, aren't high enough for 
soundboard movement to anywhere nearly account for the pitch 
changes we regularly find. The soundboard would have to rise 
and fall 10mm or more in some cases, and they measurably DON'T 
move remotely that much.


>Also the soundboards often crack after being 
> here a while, and many techs advise that they get a room humidifier 
> and/or Dampp-Chaser system.  But in Boston, when the furnace is running 
> all the time during a cold winter, aren't most homes there just as dry?
>        --David Nereson, RPT

I don't know, are they? I lived in Denver for a year, and it 
was very dry there year round. How about Boston?
Ron N