False Beats

[Ron Overs]

David, Ron, Richard and list,

David wrote;

>. . . .   I can think of hundreds of grands, especially
>Japanese/Korean, where I could visibly see the string drop to bridge cap.
>Another tap wouldn't move it.  

So often these makers use bridge pin inclinations which are insufficient and a string offset angle which is often below 10 degrees.

I learned a lesson the hard way a recently. Ten degrees of string offset angle and twenty degrees of pin inclination certainly works well.

In July we completed a new piano for the Australasian Piano Technicians Convention. The piano was a modified Samick 225. We designed a new scale and made new bridges, along with many other design changes. This piano was the first to get our new grand piano action.

However, during the design phase of this project, which was rushed to say the least, I made an error in a spreadsheet formula while working out the bridge pin locations to set the string offsets. Unfortunately, this error resulted in string offsets which were pretty close to zero in the top two sections. I discovered this problem just before the piano was to be strung, and too close to the convention to rectify. Therefore, we were compelled to string the piano, warts and all, since it was to be an exhibit at the convention.

I was not too pleased with the tonal qualities of the treble section. While it was just acceptable, it had none of the clean tonal qualities which I had expected. Indeed the piano was so false as to be difficult to tune. After the convention we stripped the piano down and recapped the offending sections. We are now delighted with the tonal qualities of the treble. The only difference between the two bridge caps was the string offset angle - yet the tone was radically improved.  For the second take, the bridge pin positions were transferred from the spreadsheet to a CAD drawing of the piano. The drawing scale was adjusted to produce an accurate 100% print out on our Epson inkjet. The print out was placed on the blank bridge caps, which allowed us to punch the marks through to the bridge cap. Using this system we were able to get the highest bridge pin location accuracy we have had to date. I have suspected for while that insufficient string offset angle to contributes to falseness. The bungled bridge cap saga prove it!

>  I have a 1870 or so, factory rebuilt, Bechstein grand that has some
>of the worst falseness in the treble...5 beats a second if you can believe
>it.  

Typical of Bechsteins of the period. Is the bridge pin group parallel to the capo bar?
Bechsteins usually do not comply - a highly suspect practice.

Ron Ns post was very interesting.

>. .  installing bridge pins
>was that it was crucial that they be seated at the bottom of the hole . . 
> to improve the termination and minimize, if not actually
>prevent, false beats. For a long time, I didn't question that until I
>started playing around with false beats to try to establish a cause and
>effect relationship for myself. What bothered me most about the "bottomed"
>theory was that anything that critical in theory ought to be pretty obvious
>in practice and that didn't seem to me to be the case. Years back, I had an
>old grand in the shop and hadn't torn it down yet, so I thought I'd see
>what I could break. I located a half dozen or so clean sounding strings
>among a whole bunch of false beaters and did some experimentation. Choosing
>a clean note, I tapped the bridge pin lightly with a hammer and punch. It
>moved down a millimeter or so and seated. It hadn't been seated before but
>sounded clean. It was also clean after seating. Trying a number of others
>just like it produced similar results. Well, it didn't seem to do any harm,
>I wonder if it will do any good. Choosing a beating string, I seated it's
>front pin. The beat lessened. Aha, improvement! Trying others, I found that
>some got pretty and clean, some were slightly improved, and others not
>noticeably changed. So much for the first blush of success. Since that
>procedure didn't seem all that conclusive to me, I chose a few more beaters
>and *turned* the front pin about 20° to get an un-worn surface under the
>string. That had approximately the same effect as tapping, but the pin
>hadn't been seated at all! Aha again! Next, I played each note with the
>turned pin, listened to the false beat, seated the pin, and listened again.
>Seating again seemed to improve some of them, but the difference was to my
>mind negligible. Aside from reinforcing the ever growing suspicion that my
>mind is negligible, this seemed to indicate that getting the string out of
>the old wear track in the pin was what made the most difference, whether by
>turning or seating the pin. That, however, isn't the point here.
>
>Seating bridge pins in the bottom of the hole may be beneficial, or it may
>not. I just haven't seen or heard anything to indicate to me that it makes
>a real difference. I have, however, seen and heard enough to convince me
>that the wear track on the pin is a contributor. That's primarily why I
>recommend tapping pins in slightly, instead of seating strings on bridges,
>to try to minimize false beats in field work. I know this is old
>installation stuff instead of the new we were discussion, but it ties in
>and is all part of my reasoning.
>
>I've tuned a lot of new to ten year old pianos with long pointed pins that
>were originally bottomed out in their holes and filed on top that weren't
>any cleaner - and occasionally much wilder - than my too deep holes with
>pins driven to finished height bridges of similar ages and usage conditions.

>I have no doubt that Ron O knows things I don't

I wouldn't be too sure of that Ron!

> and I know I'm not too
>alert at times

I not too convinced about this either.

Interesting posts guys.

Ron O

Overs Pianos, Sydney Australia
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Email:   sec@overspianos.com.au
Website: www.overspianos.com.au
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