Stretch tuning a resistor string... why NOT to!

[Ian Fritz]

----- Original Message -----
From: KA4HJH <ka4hjh at gte.net>
To: <synth-diy at mailhost.bpa.nl>
Sent: Sunday, January 16, 2000 10:56 PM
Subject: Re: Stretch tuning a resistor string... why NOT to!

> As I understand it, in the real world elastic materials become more
> resistant to being deformed the more rapidly you try to deform them,
> and so the deformation gets propagated more rapidly. In other words,
> the higher the frequency, the stiffer the wire, and the higher the
> frequency.

I really doubt you see any effects like that in piano wire at audio
frequencies.

The reason the harmonics of a piano string go sharp is because of the finite
thickness of the string. (The usual simplified textbook picture assumes zero
thickness.) As frequency increases the wire becomes stiffer because the
string radius is a larger fraction of the wavelength, or to put it another
way, because the curvature of the deformed string is higher at high
frequencies. The string becomes more like a bar. The relevant derivations
may be found in Morse and Ingard section 5.1.25.

 Ian