[pianotech] Bridge pin locations help (image oops)

[Roger@Integra.net]

Ron,
Well, I guess we'll agree to disagree about the string seating verses loose 
pin. I believe the seating process is effective because the string is now 
laying flat against the bridge cap. I've found that false beats can be 
reduced or eliminated by seating, on both new pianos out of the crate that 
don't have loose pins and strings on 90 year old pianos that obviously have 
loose pins. This points to the cause of these false beats to be created by 
poor termination on the bridge cap. I believe most manufactures recognize 
the importance of the uniform termination by applying great care to ensure a 
perfect string and notch alignment. I must emphasize that I'm not 
discounting loose pins as the cause of false beats but pointing to other 
sources as trouble.

As for the screwdriver test. Listen closely when applying pressure to the 
pin with a screwdriver. In those instances when a loose pin is not the 
cause, the false beat is reduced in strength and duration but not speed. 
I've found this to be the case on many Yamaha pianos. To acknowledge this 
effect may point you to something else, such as a poor termination on the 
opposite end of the string. That's the tree I was referring to.
Roger Gable

----- Original Message ----- 
From: "Ron Nossaman" <rnossaman at cox.net>
To: <pianotech at ptg.org>
Sent: Friday, February 04, 2011 4:39 AM
Subject: Re: [pianotech] Bridge pin locations help (image oops)


> On 2/3/2011 11:22 PM, Roger at Integra.net wrote:
>> Ron,
>> I would have a tendency to disagree with your analyst.  First, if a false
>> beat was usually caused by a loose pin (which it frequently is) then
>> there isn't a rational reason why string seating cures a major portion
>> of false beats.
>
> Seating sometimes stops the beat because it jams the string against the 
> bridge cap hard enough to stop the pin flagpoling - sometimes.
>
>
>>What seems more rational is that the seating process
>> beds the string against the pin and bridge to create a uniform
>> termination during the entire circular motion of the string -- remember,
>> strings rotate, not just move up and down. In the situation pictured,
>> the rotational movement of the string would indeed vary the termination
>> length and/or create an "energy leak, or skip" past the termination
>> sometime during the rotational cycle. That picture "screams" of an
>> situation where the energy can't be uniformly reflected back into the
>> string during the entire rotational cycle.
>
> Again, the pin is the termination in all directions of string termination 
> unless the notch edge extends into the speaking length. The string doesn't 
> slither up and down the pin except perhaps the first millisecond of the 
> attack impulse, well before the beat can be heard. The friction between 
> the string and pin doesn't allow it. The beat comes from the different 
> "effective" speaking lengths caused by the more rigid termination in the 
> vertical direction, and the springy termination in the horizontal. That's 
> why the screwdriver test works.
>
>
>> Your mention of using a screwdriver to temporarily "stake" the pin for
>> testing is, in my opinion, suspect many times. When the false beat seems
>> to be reduced or disappear during this test, you will, with close
>> examination, find that you are not always hearing the effects of a more
>> solid pin, but only the result of a dampened bridge cap, giving you the
>> impression that the false beat has disappeared.
>
> Close examination? What method do you use to indicate a "dampened" bridge 
> cap? And how do you get an impression that the beat disappeared if it 
> didn't? If the screwdriver "damps" the cap, then you can push directly on 
> the cap and get the same effect, or on the adjacent pin. This isn't the 
> case. Have you actually tried it? The beat suppression is a direct and 
> repeatable result of stopping the pin flagpoling, and it doesn't take much 
> pressure to do it.
>
>
>>This is not to say that
>> the screwdriver test is an invalid test, but is to say that you may find
>> yourself barking up the wrong tree.
>
> No, I'm not. How about you inform us what, specifically, is a valid test 
> that barks up the right tree?
> Ron N
>
>