Humidity Change and Unisons

[Ron Nossaman]

>Hi  Ron,
>
>So it *is* the red felt in the casters after all? LOL
>
>Seriously I would love to see the sort of research you suggest. But lets
>agree that the plate moves with humidity change. And further that most
>pitch correction is plate related more than sound board related. 

Hi Don,
No, let's not. The movement of the soundboard and bridge relative to the
plate is the major culprit. As far as I know, cast iron doesn't measurably
change dimension with humidity swings, only temperature. Wood does. I'm
going with the observable. Incidentally, that wasn't a research proposal.
It's a logic exercise.



>One *hint* again is that damppchaser bars under the soundboard do *less*
>than bars at the belly and tail. To me that indicates that drift is plate
>related more than soundboard related. 

I haven't tried it, but if that's the case, to me that would indicate that
different bar placement locations produce different air convection and
dispersal patterns underneath - some more efficient than others. I don't
get a connection with the plate at all there. Perhaps it's just a case of
"warm tail, happy piano". Maybe it's time to re-design my business card.
<G> I kind of like it.



>The smearing of the unisons is also very real and can be measured. Simple
>sound board movement I don't believe could be responsible for this type of
>drift.

I didn't say it wasn't real. I just attempted an explanation as to how it
got to where you found it. The soundboard movement is relatively simple,
it's all the friction and tension interactions along the string length that
get complicated, and the only data we have there is pitch measurement in
the speaking lengths.



>Then too, apparently (I have not noted this but will accept that others
>have measured it carefully) pianos with aliquotes or *double scaling*
>appear to be more stable. If this is true then the hitch pin / string angel
>is where atleast some of the unison smear is happening. 
>
>These are just hints nothing more.

This may very well be real too, but I doubt it's the aliquots that make the
difference. I'd think it's the longer total backscale length. 

Most of the mysteries we see can be explained by what we already know.
Determining what we already know seems to be the hard part.

Ron N