The article that David P linked was helpful if you follow the math.
Let me try to put it in more simple terms. Impedance is, roughly speaking, resistance to motion. If you're pushing a dead car across a level parking lot, impedance is a measure of how hard you need to push it (basically related to friction and mass of the car). Vibrating systems like a piano string are a bit more complicated.
Imagine yourself holding one end of a garden hose that is stretched tight between you and the faucet. In this case, impedance is the answer to the question, "How hard to I have to waggle this end to get the whole hose to wave up and down?" The answer depends on the tension and linear mass density of the hose.
Tension: if the hose is stretched really tight, you have to waggle it really hard to get the same height of waves that you would get on a loose hose.
Linear mass density: It requires more force to waggle a fire hose instead of a garden hose.
The impedance is the square root of (Tension x Linear mass density). If you increase the tension or the weight of a string, the impedance goes up. In the article that David linked, the impedance is "Z", the tension is "T", and the linear mass density is "
ρ" (Greek letter rho). So Z=√TρThe reason impedance is important is that it is a factor in how quickly energy is passed between vibrating systems. Note that the soundboard has its own impedance. (Think how hard the string has to waggle the bridge in order to get the soundboard to vibrate.) If the impedance of the strings are close to the impedance of the soundboard, energy transfers very quickly from the string to the soundboard and you get a loud "Whomp" with no sustain. We want the energy to transfer slowly from the string, but not too slowly, otherwise the piano sounds weak.
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Anthony Willey, RPT
http://willeypianotuning.comhttp://pianometer.com------------------------------
Original Message:
Sent: 01-01-2021 12:11
From: Chris Chernobieff
Subject: String scale question- Impedance?
I was reading this article:
https://www.quora.com/What-is-the-velocity-of-sound-through-steel-if-Young-s-modulus-and-density-are-given?share=1
and it appears that the velocity of a sound wave through a material does not depend on its mass. If the numbers change just because the lengths change. I don't understand the value of the Z numbers on the stringing list. And that is regards to speed. As to stiffness of the wire, isn't that what inharmonicity shows?
-chris
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Chernobieff Piano Restorations
"Where Tone is Key"
chernobieffpiano.com
grandpianoman@protonmail.com
Lenoir City, TN
865-986-7720
Original Message:
Sent: 12-29-2020 15:16
From: David Pinnegar
Subject: String scale question- Impedance?
An interesting question
are possibly helpful places to start.
Best wishes
David P
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David Pinnegar, B.Sc., A.R.C.S.
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+44 1342 850594
Original Message:
Sent: 12/29/2020 2:36:00 PM
From: Chris Chernobieff
Subject: String scale question- Impedance?
A friend of mine and myself ordered a string scale from Del Fandrich. We were perplexed by one of the parameters that was called String Impedance. There was no units of measure to go by so we were wondering what the numbers were telling us and how it was derived. Maybe Del or someone else could explain. Thanks in advance.
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Chernobieff Piano Restorations
"Where Tone is Key"
chernobieffpiano.com
grandpianoman@protonmail.com
Lenoir City, TN
865-986-7720
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