Bridge Seating

[David Ilvedson]

So Ron,

Do you find you are applying CA a lot to bridge pins?   In other words it seems to really help?

David Ilvedson, RPT
Pacifica, CA  94044


----- Original message ----------------------------------------
From: "Ron Nossaman" <rnossaman at cox.net>
To: "Pianotech List" <pianotech at ptg.org>
Received: 9/9/2006 3:09:42 PM
Subject: Re: Bridge Seating




>> *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