Downbearing----Sustain?

[Michael Wathen 556-9565]

I have carefully read Mr. Hartman's articles regarding the
effects of Downbearing.  The first installment was well put
together and it is the kind of think we need to see more of.  Mr.
Hartman explained the principles involved in a clear and
inventive way.  He has taken care to use terms and concepts that
are well defined and understood by a broad scientific community.

Since these concepts are well known and can be referred to in
countless in texts there is no need to reference anything.
Speaking for myself, I fell confident that I can check any of his
arguments by looking it up quite easily without any quoted
reference on his part.  However, at the end of the first
installment he illustrates the typical modes of soundboard and
the spectrum of a soundboard driven at two frequencies; these are
not referenced.  I am left to wonder; where did he get this
information?

It is complicated further by his second installment.  He speaks
of energy being shifted to lower modes by the stiffness provided
by downbearing.  This is contrary to everything I have ever
understood about the subject.  Does he have sources or is it pure
speculation on his part.  Has he performed some type of
reproducible experiment that shows this.

My own reasoning leads me to <believe> that a stiff bridge
divides the board's modes up into smaller areas by acting as a
surface node.  It would be much like striking a string with your
finger lightly touching a cross section of the string. This would
restrict the string from vibrating for any wavelength that was
both greater and not an integral length of the distance between a
termination and the finger.

My own understanding leads me to appreciate just how great is the
Baldwin acujust hitch pin that allows one to to have uniform
downbearing angles and limit it to a reasonable small angle. The
next greatest thing one can do is design a string scale that has
uniform tension.  Uniform tension translates to uniform
downbearing force from note to note if the down bearing angles
are all the same.

Finally, the idea that greater downbearing means more sustain is
something that I have not been able to verify.  I have a
monochord with a twenty inch speaking length (C#3 at 160 lbs
tension, I believe).  This string is excited by a grand action
model.  A fixed weight is set on the key to provide a fixed
velocity for the hammer to excite the string.  One end of the
monochord has an acujust hitch pin so that I can control the
downbearing on the wooden bridge.  The other termination of the
string is a mounted agraffe.  A transducer is attached that
consists of a six inch copper strip. It measures the change in
the electric field as caused by the moving of the string which is
acts like the other side of a capacitor.  This signal is captured
by an Analog to Digital board in my computer and the software
graphs the changing voltage over time.  I took six samples each
at a different downbearing angle.  I could find no correlation
between downbearing angle and the sustain, as you call it.

Now to be rigorous it would be best to take maybe thirty scans of
each downbearing angle and then average them and check for a
correlation again.  Perhaps I might try this in the future.
Also, my monochord is mounted on an aluminum I beam not a piano
soundboard.  But, with this model I really am checking the
sustain or the dampening of the string independent of the sound
that is produced.  In other words it is measuring the movement of
the string and not the sound that is produced.

If Mr. Hartman has references I would like to know them.