struck and unstruck plane

[Michael Wathen]

Here is the explanation I promised about the traces.  We made a monochord.
The foundation for the monochord is an aluminum I beam.  To the I beam are
mounted various things.  The string is tied in a loop which is attached to
an Accu Just type hitch pin. Next it passes over a small bridge with two #7
bridge pins.  The setup on the bridge is the same as would be found on a
piano.  The other end of the string terminates by passing thru an agraffe
and down slightly to the tuning pin.  The downbearing is adjusted by raising
or lowering the string on the hitch pin.

The notes are all the same tone.  I don't have my note book in front of me
but I believe that it was C#3.  I think the string length was about 78 cm.
The string gauge was #19.

Also attached to the I beam is a transducer.  The transducer converts the
mechanical energy of the string to electrical energy.  It consists of two
thin copper plates about 0.4 cm x 8 cm.  One plate is positioned so that it
is parallel to the struck plane and the other is set perpendicular.  Both
plates are about 0.4 cm from the string.  A power supply provides a charge
to the plates and the change in the electric field is measured for the
string in motion through each plate separately and independently.  The
signal is then sent to a signal analyzer which records and processes the
information for the graphs.

This whole I beam assembly is fastened to a grand action model.  A uniform
blow was provided by lead weights on the end of key.  The traces you see are
the result of twenty five scans averaged out.

These traces are 2 second intervals.  The X position for each graph
indicates the peak amplitude.

We tried many types of bridges and ways of terminating the string on our
monochord.  We found that even if you terminated the string with a steel
roller or any other method you always got a significant string motion in the
unstruck plane.  So for Mr. Coleman's question, from what I have seen
circular or near circular motion is next to impossible.
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Michael Wathen				Fax: 513-
Piano Tech ML 0096			tel: 513-556-9565
Colleg-Conservatory of Music
University of Cincinnati
Cincinnati, OH 45221-0096

http://www.uc.edu/~wathenmj (personal)
http://www.uc.edu/~wathenmj/piano.htm  (Piano Tech Department)