Bridge Seating

[Ron Nossaman]

> *Now, as for the cause, we have to start from the very beginning. A 
> false beat is two different frequencies produced by the same string. To 
> have two frequencies produced can only be caused by changes in either 
> the speaking length or a change in the tension of the string. What is 
> the actual mechanical link between a loose bridge pin and either of the 
> above causes? Does a loose bridge pin create changes in tension or 
> changes in the speaking length of the string?*
> ** 
> *AF*

Neither. It's a soft termination problem.

Strings assume an elliptical excursion path as they vibrate, 
so they're going both horizontally, and vertically. The 
termination at the bridge is the pin, not the notch. During 
the vertical part of the excursion the string is solidly 
terminated by the pin, which is firmly embedded and doesn't 
move vertically in the bridge. If the notch edge is crushed 
and the pin is even a little loose at the very top of the cap, 
the pin will flagpole with the horizontal part of string 
excursion, providing a lossy termination, and producing a 
lower frequency then the vertical excursion. The difference 
between those frequencies is the beat. Seating the string 
temporarily mashes it down on the notch edge enough to wedge 
the pin back and, sometimes, prevent the pin from flagpoling, 
temporarily clearing up the beat. The test of touching the pin 
with the screwdriver keeps the pin from flagpoling, and almost 
always kills the beat. There are other causes of falsness, but 
the one that is "fixed" by string seating is caused by loose 
bridge pins.

Ron N