[CAUT] False Beats and wood

[Don]

Hi all,

I was reading through the five lectures again--been a while. 

In the coupled motions article the point is raised that the bridge is a
springy termination which cause the string to "think" it is longer than it
is lowering the frequency.

Ric has asked often why a screw driver on a bridge pin may initially stop a
false beat but when more pressure is added the beat may start up again.

The simple answer may be that adding "apparent" mass by touching the screw
driver makes the pin less able to spring--but as pressure is increased past
a certain level, the frequency will begin to change--causing a return of
the falseness. If this is the case then as Ric increases the pressure the
beat should change it's speed (that is until the screw driver slips off and
makes a hole through the soundboard *grin*).

As a side issue it may also offer an explanation of why CA glue works. It
may simply makes the bridge a bit denser--providing a more support--making
the wood less springy. I.E. It hasn't got much to do with the bridge pin
being loose—it has to do with the wood failing to be dense enough. That
nicely explains why a bridge pin can be so loose it can be removed with
just your fingers—and still not produce a false beat, or it can be so tight
that a captive hammer is needed to remove it—and still produce a pronounced
beat.

Here is the quote (out of context) from the article that got me thinking
along this direction:

"If the support is "springy," that is, one which displaces sideways in the
direction in which the string applies a force to it, there will no longer
be an exact node at the support. Instead, the extrapolated node will be
somewhat beyond the physical end of the string; or, in other words, the
string will "think" that it is longer than it really is, causing it to
lower its frequency."

Comments?
Regards,
Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T.
Non calor sed umor est qui nobis incommodat

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