M&A A

[piannaman at aol.com]

It isn't ALWAYS bridge pins.  I suspect the reasons for false beats are many.
 
I got a call from a prospective client who was complaining of a false beat at the tenor treble break area (Maybe one note removed to the treble side).  Very bright chap.  He tunes his own piano sometimes when he can spare 5 hours, but doesn't want to do any technical work.  He was interested to know if his brand new Kemble grand's false beating note could be remedied by string replacement.  Like the other techs he asked, I was somewhat dubious that it would work, given its location and all.  But, since he agreed to pay for it and try to get reimbursed by Kemble, I agreed to give it a shot.
 
Sure enough, the offending beats disappeared with the replacement.  That was proof to me that while bridge pins may often be the cause, there may be other causes as well.  
 
 
 Dave Stahl





 
 
-----Original Message-----
From: ricb at pianostemmer.no
To: pianotech at ptg.org
Sent: Sun, 18 Feb 2007 3:41 AM
Subject: M&A A


Hi Paul. 
 
The variability of beat speeds you mention bothered me as well for a long time. But lots of reading on the subject removed my objection per se. What finally made the light go on there was Jim Ellis's article from way back. He used a pendulum analogy to show that the degree of springyness a support (i.e. termination) has can essentially lengthen the effective arm of the pendulum and slowing the period. It does this by moving in phase with the oscillation of the pendulum. The more springyness, the greater the complimentary oscillation and the faster the beat rate. That in itself tho leaves one with a single slower frequency... not two frequencies needed to create a beat rate. Ok... so a string vibrates at many frequencies... but it still would need to have to simultaneous nearly identical lengths for a beat rate to happen... and this needs to happen at the termination..... Ok again... the string can vibrate at same frequencies in several different planes at the same time... and then this becomes possible... at least as far as springyness of the termination in general is concerned. 
 
The problem with fitting a loose pin into this as something that <<directly causes>> false beats is that one attempts to go back to Jim's article... define the pin as the pendulums <<support>> and as such must claim horizontal movement of the pin as being the culprit. This gets problematic immediately. Jim himself denies that (stricktly) horizontal movement of the pin.. or that any in phase movement by the termination in any /particular/ direction at all is at root. In phase movement at the termination occurs in all directional planes of string vibration. He cites general springyness of the termination as a whole, tho is the first to go along with the idea that bridge pins can be a contributing factor in the general condition. I also wonder about the sidebearing of the string in this picture... it would seem to me that even if a loose pin was involved.... the least likely direction for in phase springyness would be the horizontal exactly because of the side bearing the string has. 
 
Then there are some empirical facts that simply cant be ignored. Purely from a statistical standpoint there is really no identifiable correlation between the occurance of false beats and loose bridge pins. Way to many cases where the opposite happens... way to many cases where the same false beat occurs when pins are actually tight. Then there is also this famous <<test>> with the screwdriver. Why does pressure with the screwdriver actually cause the false beat to start up again and speed up with more pressure when you've first put enough pressure on the pin to quite a false beat ? Why does the application of mass to neighboring bridge pins or back side pins also (sometimes) affect the presence of a false beat ? 
 
Strikes me that the whole presently and popularly accepted idea that bridge pin is /thee/ support for the string and that it /causes/ false beats is a pretty large oversimplification of the whole thing.... likely based on an equally over simplifed interpretation of articles like Jims. And as is very common in our trade the collective we jumps on the wagon declaring a new (and just as magical as any previous) Truth . Viola ! 
 
For my part.... I'll keep adding CA in appropriate circumstances... because it does help... (another discussion entirely :) )... but I'll also keep wondering about what the heck is really causing false beats. Clearly the loose pin thing is to thin. Actually... when it comes down to it... the recessed notch bit seems much more likely as it allows the string itself to have a partial vibrating in several planes at the same time at different lengths... the bridge pin doesnt need to even get involved here. For that matter... string imperfections at or very close to the termination can cause a string internal springyness that could be at root. The whole thing needs IMHO a lot more looking into before any definitive explanation is available. 
 
Cheers 
RicB 
 
  Ric: 
 
  What has always struck me about that particular mythology is the 
  variability of beat speeds in real (false) beating. Attributing it 
  to loose bridge pins would lead us, no?, to believing that the loose 
  bridge pin is moving in some way in the bridge pin hole, wandering 
  in some oscillating manner that would create a "countable" beat, 
  sometimes as slow as one beat per second, and certainly much faster 
  in most instances, but still regular and countable. I share your 
  skepticism, and return again to some length differential being 
  created in the speaking length by way of termination deterioration, 
  particularly the notch part of the termination creeping forward in 
  the curve of the notch and creating a separation from the ideal 
  simultaneous contact of the string at pin and bridge top. This is an 
  old can of worms, I know, but maybe worth revisiting. 
 
  Paul 
 
  IF YOU WANT TO KNOW THE TRUTH, STOP HAVING OPINIONS! 
 
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