[CAUT] M&H crown device

[Bob Hohf]

It's not that hard to investigate this sort of thing, which Dave Carpenter
and I did a number of years ago while preparing a seminar for the Chicago
School.  I don't have time at the moment to get into a long discussion of
this, but will toss our grist into the mill FWIW.

 

I made a toy soundboard, like the M&H device, on which we could gauge the
amount of flex along the grain.  It had 3 sockets for tuning forks: one at
1/2 the length, one at 1/3, and one at 1/4.  We put a vibrating fork in the
middle and flexed the board while Dave measured it with some sort of
spectrum analyzer he had lying around. As we gradually increased the flex, a
distinct "node" appeared where the 2nd partial jumped out of the spectrum--a
little more flex and it disappeared.  This is the point where the salesman
raises his eyebrows and the customer goes, "Oooooooo...."  A little more
flex and another, weaker node appears for the 3rd partial. Move the fork to
another socket and the same thing happens but at different degrees of flex.
Using a different pitch fork does the same thing with different flex.  Dave
and I spent the better part of a morning doing this with different pitch
forks accumulating quite a pile of data. When we graphed it, Dave thought he
saw the beginnings of a complex pattern, but all I saw was a bunch of dots.
As Del and Ron have already said, this data means very little because real
soundboards are not crowned along the grain--at least not nearly enough to
produce this sort of effect.

 

So make a similar device that can be flexed across the grain the way
soundboards are crowned, and what happens to the spectrum as you flex it?
Nothing.

 

Draw your own conclusions.

 

Bob Hohf

Wisconsin

 

 

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