impedance and empericism -- longer

[Ron Nossaman]

>I am asking if soundboards DO have inharmonicity?   If so, how do you find
>out how much?   We have the experiments of R. Young for steel strings.  If
>suggestions of Ron and I for Ih for soundboards are true, they would have to
>be verified by experiment.  But how would these experiments be set up?

What suggestions have I made that soundboards have inharmonicity, other
than to acknowledge the possibility? I did agree with posts observing that
soundboards affect measured string inharmonicity, but to my mind, impedance
and resonant frequency are the base concepts. Just like in a string,
changing weight or stiffness, and therefor impedance and resonant
frequency, would affect any measured "inharmonicity" in a soundboard, which
makes soundboard "inharmonicity" a secondary definition of something that's
already covered by impedance.  



>,... This discussion started about humidity affecting inharmonicity.   I
>noted that the research on inharmonicity only considered it as an effect of
>a vibrating steel wire.
>No parameters were given to include effects of humidity.  Now inharmonicity
>readings from ETD's are apparently different from day to day.  What is
>causing the difference?

The soundboard. The strings don't exist in isolation, perfectly terminated
and driven. They are connected to, and affected by the soundboard. As the
moisture content of the soundboard assembly changes, so does it's mass and
stiffness, and thus it's impedance and resonant frequency at any given
point on the scale. All that is measurable, has been measured, and depends
on a whole lot of not easily determined factors to accurately predict
before the fact. While the strings are moving the soundboard, the
soundboard is moving the strings too. When the stiffness and mass of the
soundboard change, it moves differently and, in turn, moves the strings
differently too. String inharmonicity is computed or measured for one
string, or oscillator. That oscillator, along with 230 more with different
inharmonicity values is coupled to one large multi-rate oscillator whose
measured oscillation frequency and harmonics is dependent on the point of
measurement and the current moisture content. That's one string. How about
the other 230 measurements at the point where each string terminates on the
bridges? Now what's the "inharmonicity" value for this particular
soundboard at this particular temperature and humidity, or the impedance,
or resonant frequency for that matter? How do you separate the affect of
all the other strings that are coupled to the soundboard and modifying it's
responses, from the individual one you are trying to measure? You don't,
and that's the point. What you can do easily enough with a computer and
Tunelab, is measure inharmonicity in any given string on any given
soundboard at a variety of temperature and humidity conditions and observe
the effect for yourself.


>  We need to devise a simple
>experiment.  Compare the partial readings of a string between two clamps to
>one of the same length on a sound  board.  Keep a record over varying days
>of humidity and temperature.  Which changes the most?   Is this a valid
>experiment to arrive at an understandingof the effects of RH on IH ?
>---ric

Sounds like a reasonable start. Let us know what you find.

Ron N