Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Speaking and non-speaking length tensions

Following Jeff Deutschle's super demonstration/proof about tuning pin twisting, what 'd be fascinated to see, would be a demonstration of the tensions in the speaking and non-speaking lengths of a tuned piano string.

Over the years, I have read statements that stability is achieved when tensions are 'evened out' between the speaking and non-speaking sectons, and statements that stability depends on higher tension in the section between tuning pin and agraffe or V bar and/or pressure bar helping to keep the speaking length at pitch.

It would be fascinating if it were possible to inset strain gauges into those lengths, just to see!

Had the same thought, but not so much about stability as about how the tensions in SL and NSL change. See, the amount of max difference in tension between a SL and NSL is dependent on the amount of bearing friction. At a certain percentage of that max difference, we would consider the string to be stable.

OK, there's many factors, and I feel I might be rambling. Here's an experiment I thought of. Maybe somebody else's turn to do one. (Still have some firewood to cut if the snow ever melts, and a van with body cancer that is due for inspection.) Make a mock-up of a string and tuning pin arrangement with 1 SL and 2 NSLs. Each segment being a whole ratio of the others like the SL being 12 inches, one NSL being 3 inches, and the other being 1 inch. Include a "Twistometer" gauge like I made for the twist demo and somehow make the friction of the bearing points adjustable. If the string path was a "Z" and the bearing points were tuning pins ground into ellipses, turning the pins would make the bearing point sharper or duller, thereby changing the friction. By listening to the SL and NSLs while plucking, the resulting just intervals that would be heard will tell if one section has more or less tension than another section. (Think about it...) A frequency meter would be helpful for documentation.

To continue rambling, as I know what it is I wonder about, but not confident in expressing it... Ken Burton's book "Different Strokes" on hammer technique talks a great deal about how the proportional relationship between bearing friction and pin torque helps determine the appropriate hammer technique. (Gotta apologize, I haven't read it for a number of years. I am going by memory.) The idea is that if when pulling up to pitch, the pitch stays there when releasing torque, the SL and NSL are at the same tension and the string is stable. This would be because the extra tension in the NSL necessary for the strings to render on the way up, are relaxed the required amount when torque is removed from the pin and the pin untwists. BUT IS THIS REALLY SO? And is there a window of stability, and when there is more than one NSL, would both those lengths end up with equal tensions (I doubt it...), and do they need to be? And one other question is about the residual torque in the pin being a factor when an actual tensioned string is involved. And what about flagpoling?

Ugh, might be better to just get a copy of that university study someone mentioned. But then again, seeing (and hearing) is believing.

Gosh, I hope someone else is up to this challenge...

Oh, and it would be best if this was done with someone with an impact tuning lever so we can see if it truly turns the entire pin without twisting and renders the strings at the same time. Maybe someone from Missouri, the Show Me State.

Possible approach?
The physics used to determine the pressure exerted on the bridge due to string tension and bearing offset may give at least some information?
So if you use the formula to calc the pressure of let’s say note 88 at 50 mm speaking length (other note 88 lengths omitted for ease of thinking) at 0.5 mm bearing or bridge height above string plane and have an accurate method of weighing the bridge and the downforce and this pressure is measured/weighed at something less than what is calculated then the difference is proportional to the tension loss across the bridge.
Make any sense?

It would require making a rigid enough bridge segment that had a very accurate scale under it.
Probably not realistic. Fun to think about though.

I wasn't considering having a bridge at all, just a hitch pin, probably a tuning pin as a substitute. I am not a believer in there being any significant change in tension of the bridge string sections while tuning. Someone could do a demo on just that, I suppose...

Perhaps a lucrative government grant could be pursued and one could spend the next ten years researching the matter (and living a comfortable life). TIC

Peter Grey Piano Doctor