Measuring soundboard thickness

[V T]

Hello List,

I am sure this is old stuff for those of you who
design soundboards, but I will post it anyway.  I
often wondered about methods of measuring soundboard
thickness, once the board is installed.

I was in a violin shop today and saw how violin makers
do it.  The tool is so elegant and simple!  It
consists of a small magnet and a spring loaded tool
that visually resembles a long syringe.  I have no
idea what this tool is called, so I will just call it
"syringe".  Inside the syringe is a spring, one end of
it attached to an iron disk (or possibly another
magnet).  The other end of the spring is attached to a
handle that sticks out of the syringe.  The function
of the syringe is to contain the spring and it has a
calibration scale on it as well.

The magnet goes inside the violin body.  The syringe
is on the top.  The little magnet is attracted to the
iron disk in the syringe and the attracting force is
related to the thickness of the intervening wood. 
When you pull on the spring, it stretches and
eventually the force from the spring is approximately
equal to the attracting force between the iron disk
and the magnet.  At that point, the magnet drops and
you hear the impact.  On the calibration scale on the
syringe, you can read off how thick the wood was at
that spot.  Then, you let the spring retract, the iron
disk is near the violin top again, and if you move the
violin body, the magnet finds the plate again.  You
can slide the tool over the top and map out the
thickness.

Vladan


		
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