[CAUT] False Beats and George Winston

[Ron Nossaman]

> My recollections here are that the pins remain high when the bridge 
> shrinks back down.  Dry weather is when I seem to find pins floating up 
> off the bottom needing to be tapped.  

Dry weather is indeed when false beats are the worst. What 
indication did you have that the pins were floating off the 
bottom and needed tapped, other than hearing a false beat and 
assuming the pins were floating?


>Is it not plausible that increased 
> downbearing in humid seasons is what reduces the falseness?

It might be contributory, but I don't think it's significant.


  > It seems the pin would have to wallow the hole at the 
bottom if it is
> flagpoling at the top.  That energy has to go somewhere.

I see. There is very little side stress at the bottom of the 
hole. It's all at the top, where the hole oblongs and makes a 
nice gently curved funnel for the pin to spring and flagpole 
in. Look at the leverage ratios. The side stress on the pin is 
0.015"-0.018" (thereabouts), and the point of support to that 
stress is ideally at the bridge cap surface, but moves farther 
down into the cap as the wood crushes. Even if the pin is 
presenting 0.050" of unsupported pin between the point of 
support and the string contact, the bottom of the pin is under 
less than 1/10 of that string bearing load. Remember the old 
advice that if you can't easily pull the pins with pliers, 
they're ok, and it's ready to string? Well, it's not. If there 
were flagpoling pin induced false beats before stringing, 
they'll be there with the new strings too unless the pins are 
at least CA'd, regardless of how tight the pin is at the 
bottom of the hole.


> Without having a cross section to study, or a teeny weeny camera to go 
> in and inspect the hole, I'm imagining each end of the pin flagpoling 
> with the string vibration, somewhat like holding a pencil in the middle 
> and "flicking" it.  Regardless of how many fingers or fists you hold it 
> tightly with, the pointed end vibrates when you flick the eraser end 
> unless the tip is anchored.  But having the sharpened end anchored, the 
> movement of the eraser end is further restricted (and sound is 
> transmitted more solidly), regardless of how tightly it is held nearer 
> to the eraser.  The top of the pin cannot move nearly as much if the 
> point is anchored at the bottom, regardless of how tight or loose it is 
> at the cap.

Wrong mental image. More like a yardstick partially hanging 
over the table edge and clamped down by a pile of books. Flick 
the overhanging end, and it oscillates - faster or slower 
depending on the free length. That's what bridge pins do too. 
They flex with string movement if they aren't solidly anchored 
right at the top of the cap. The produced beat rate is 
dependent on the diameter of the pin, the distance between the 
string contact point and the point at which the pin is solidly 
supported in the bridge cap, how far back from the notch the 
effective vertical string support is, and the frequency of the 
string's speaking length. Beat rates are different for each 
string because the effective point of support down in the cap 
is slightly different, as is the crushed notch edge for that 
particular string. This type of false beat only happens in the 
higher frequency areas of the piano, with the smaller diameter 
pins. That's why you don't get loose pin beats in the lower 
half of the scale. It's only in the top half that the 
flagpoling frequency can be close enough to the string 
frequency to make the beat audible.


> A simplified comparison for sure.  But, such is my mind.
> :u)

It really is a simple phenomenon once we get past a few 
entrenched assumptions.
Ron N