Bridge Seating

[David Ilvedson]

That's got to be a Sohmer with agraffes on the bridge?   I've run across the same thing and it was very false...I never tried lifting the string at the agraffe but that might make a difference...it certainly can in the normal agraffe arrangement...

David Ilvedson, RPT
Pacifica, CA 94044





Original message
From: "alan forsyth" 
To: "Pianotech List" 
Received: 9/9/2006 12:15:57 PM
Subject: Re: Bridge Seating 


I have this piano where every single string is false. I know it is not the bridge pins because there are no bridge pins. Another form of clamping the strings to the bridge is being used. ( I'll leave you to imagine what that might be.
 
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
----- Original Message ----- 
From: Ric Brekne 
To: pianotech at ptg.org 
Sent: Saturday, September 09, 2006 10:57 AM
Subject: Bridge Seating (was Re: Where to notch a bridge,& relative effects ????? (Advice sought)


List:


"Exactly right William, thank you. Johnathan, when you hear a 
string that sounds like something you would typically seat, 
try this. Place a screwdriver tip against the speaking length 
bridge pin of that string, and apply a bit of pressure to the 
side of the pin opposite the string. Odds are, the sound will 
clean up as if you'd seated the string. Take the screwdriver 
away and the noise returns. Replace the screwdriver, and the 
sound cleans up again. Ask yourself why that is, when you 
haven't seated the string at all."


I'd suggest folks go a couple steps further with this advice.  Ask yourself why if you increase pressure on the screwdriver the beat starts up again.  Also actually count and write down which strings have false beats and which of these actually reacts to the screwdriver. Then figure your percentages.  The real odds are that the percentages are somewhat more a game of bingo then anything else.  More importantly, when you are done identifying all the strings that react to the screwdriver trick and have written down each note and string,  go back through and remove each of them one at a time and check to see whether the conditions given to explain both the false beat and the fact that the screwdriver trick works are present. If this explanation was correct then in nearly every (if not all) instance you should find   1:) a loose pin, and  2:)  a deepened string mark that effectively places the notch behind the pin
 
If you actually do this, as I have on several restringing jobs to date, you will find somewhat less then half of the pins are actually loose, and that the string mark factor shows up even less often.  Since the above quote is a leading  into the loose pin / false beat proposition again, we might as well go there right off and get it done with.  Complete your researcher's ensemble by proceeding to add CA or epoxy to your pins.  Add it to ALL the pins.  When done re-identify all individual strings that show false beats.  What you will find is a general improvement of significant degree.  But closer examination of your data will indicate there is some other casual effect at work. The data shows that 1:) far from all of the original false strings are cured.  2:) some amount of the uncured are improved.  3:) there is a significant degree of new falseness on strings that were clean originally.

All this can lead you to try several different experiments in an attempt to better understand false beats.  And in the end you will still lack anything close to the definitive answer.  My experience shows clearly to me that a string is just as likely to display false beats (of the sort that reacts to the screwdriver) with the above conditions as without.  Loose pins can be downright wobbly in there holes with the string propped up with a center pin under the strings 2-3 mm behind the pin and still there is no significant degree of assurance that a false beat will or wont appear.  Try it on 20 or so strings on the next beater you get in your shop. On the other hand pins that are tight as you can ever expect them to be can also display this same kind of beat.  

There is just plain too much randomness to the occurrence of false beats if the loose pin/crushed edge explanation is applied.  

What we do know (because the rest is pure conjecture) is that the introduction of CA or epoxy significantly improves the situation. Even more so then replacing with larger pins by accounts I've heard here.  So add the stuff and be glad for the improvement.  But as far as I can see we have not arrived at an explanation for false beats.  

Cheers
RicB
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