Re: [Harp-L] Solder retune - practical limits?

[Vern <jevern@xxxxxxx>]

This is excellent information to guide the placement of solder to lower pitch. It makes reed mechanics understandable. âNeutral point" is a very useful concept. 

It confirms the theory that where you place the solder is as important as how much solder you use. The farther the solder is beyond the neutral point, the more effective it is in lowering pitch.  At the neutral point, it is ineffective and acts to increase pitch when closer to the pad. Between the neutral point and the pad, bending forces in the metal predominate and inertial forces are negligible.  Between the neutral point and the tip, inertial and restoring forces predominate and bending forces are negligible.

In a simple mechanical system consisting of a weight and a spring (and in a harmonica reed,) the resonant frequency is proportional to the square root of spring stiffness K (restoring force per unit of deflection distance) divided by weight (mass) M.  When adding solder, you are increasing the mass M (in the denominator) and reducing the frequency.  By placing the solder close to the tip, you reduce the spring stiffness that it experiences and that too reduces the frequency.

Because of the square root, you must increase the weight near the tip by about 2% for every 1% of frequency reduction.  Then you must convert frequency change to cents to determine the effect on pitch. Unfortunately, this means that huge amounts of solder are required for large changes of pitch.

Because solder is a poor spring metal, it absorbs more energy per cycle than brass.  I posit that solder on the reed between the neutral point and the pad will dampen vibration and should be avoided, especially in thicknesses great enough to increase pitch.

There is another way in which solder can be used to achieve special tuningsâattachment of the reeds to the plate by resistance soldering. Because reed location on the slot does not depend on rivet hole location in either the rivet or the plate, any reed can be installed over a slot of equal or longer length.  The tip of the reed is aligned with the end of the slot and attached.  Then the rivet holes and uncovered slot can be covered.  I posit that soldering the reed to the plate is easier and less ticklish than adding solder to the reed and the desired result can be attained with standard reeds. See https://youtu.be/DOBJCpZQ68Y <https://youtu.be/DOBJCpZQ68Y>

Vern   

 
> On Aug 6, 2015, at 5:49 AM, Rick Epping <rickepping@xxxxxxxxx> wrote:
> 
> While working at Hohner I conducted a test to see where the (neutral) point liesâ..