Re: [Harp-L] REED REPLACEMENT

[Vern <jevern@xxxxxxx>]

The (Young's) modulus of elasticity of spring brass and phosphor bronze is the same, 15x10^6.
If both the brass and bronze reeds were the same thickness near the rivet where they flex, their performance in the harp would be identical.  However the density of the bronze is a bit greater because the % of copper is higher.  This means that the bronze reed would be a bit thinner at the tip to have the same pitch.

In copper-alloy reeds, The thickness where it flexes determines the stiffness of a reed.  A stiffer reed must also be thicker at the tip to have the same pitch.

The square root of the RATIO of (stiffness where it bends)  / (mass of the tip) determines pitch.  If one copper-alloy reed is stiffer than another, it is because it is thicker where it bends, not because its material is different.  

Joe is correct that you can make a reed less stiff by shaving it where it bends.  This will make it go flat.  Then you must shave the tip to get it back up to pitch. I suppose that means you have shaved the whole thing.

If you can find a replacement reed with the correct pitch, width and length, I suggest that you don't need to worry about the material.  By time you get it tuned and playing, differences in stiffness won't be perceptible. 

IF you cut a longer reed off to fit a shorter slot, you are changing the design in unpredictable ways. Even if you can tune it to the desired pitch , unless you have Joe's unusual talent, the stiffness can be way off.


On Dec 5, 2009, at 9:58 PM, joe leone wrote:

> 
> On Dec 5, 2009, at 9:33 AM, Brian Walker wrote:
> 
>> Can a brass reed replace a phosphor reed and vs versa?
> 
> Yes, the only affect a phosphor bronze reed has is that it is stiffer. The sound should be the same. If the phosphor bronze reed is TOO stiff (action wise) and doesn't flex as quickly as the brass reed that it replaced (or the neighboring reeds), it can be 'shaved'. That means that the ENTIRE reed can be taken down a few microns.
> You know that by removing material on the rivet end of a reed you lower the pitch and if you remove material on the tip you raise the pitch. Well, if you remove material on the entire reed, the pitch can be kept the same but the reed winds up being more supple (read bendable). This can be a good thing or bad depending on how hard you play.................
> 
> smokey-joe (the Cafe s, Slim Buckston band, Stoney Brooks band)
>> 
>> 
>> 
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