Re: [Harp-L] Re: Changing a reed's length and thickness

[Vern <jevern@xxxxxxx>]

The pitch of a reed is proportional to the square root of K/M where K is its stiffness and M is its mass near the tip.  Stiffness K is affected by length and thickness near the rivet where it bends.  Its responsiveness to your breath depends on its stiffness K and its surface area.

If you shorten a reed to move it to a higher & shorter slot, its pitch will go up and its responsiveness to your breath will decrease.  Then to restore the pitch and responsiveness, you will have to remove material near the rivet. Within the outline of an optimally-designed reed lie the outlines of smaller, higher-pitched reeds.  If you know what to remove, you can usually sculpt a higher pitched reed from a lower-pitched one. 

This will not greatly affect its fatigue life unless you remove the material in too localized a part of its length and create a stress concentration.   Pitch and responsiveness limit the ranges over which you can change the geometry.  Optimum designs have been determined experimentally over the years and any radical departure from them will produce disappointing results.

Vern  

On Jul 9, 2014, at 7:50 AM, David Pearce <harpdog123@xxxxxxx> wrote:

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> I've been testing some different harmonica designs using sydel's configured plates and I would like to know what the effect of changing a reeds length and thickness would be.  Let's say you have a G note for a 2 hole draw.  What would be the effect of moving that G to a 3 hole draw and what would be the effect if you moved that G to the 1 hole draw?  I would think that increasing the reeds thickness by moving the G to hole #3 would shorten the reeds life since a thicker and less flexible reed would be vibrating vs a thinner and more flexible reed.  What would be the effect on the reeds tone?  
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> David Pearce
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