Re: [Harp-L] Reed Arc?

["Tim Moyer" <wmharps@xxxxxxxxxxxxxxxxxxxx>]

Blake Taylor wrote:
> as a struggling novice at harp maintenance, what exactly is harp 
> arcing, and how is it accomplished, and for what purpose?

Reeds are arced to a more or less degree for a couple of reasons.  
The first and foremost is simply to remove negative arc -- arcing 
downward toward the plate at the tip.  Negative arc puts the tip of 
the reed into the slot while allowing the reed length to stand above 
the slot, leaking air.  Applying a greater upward reed arc will let 
the reed tip stand above the plate leaving the majority of the reed 
length in the slot, reducing air leakage.  

The amount that reeds need to be arced is dependent on the reed 
length and desired result.  Generally, the longer the reed the more 
arc it will tolerate.  Shorter reeds don't arc well.  Long reeds 
with weighted tips are also difficult to arc, because they tend to 
want to bend in the thinner sections rather than gently curve 
throughout the weighted portion.  

> I think I get embossing, though I'm not entirely sure.

Embossing is the process of deforming the reed plate at the edges of 
the reedslot, effectively narrowing the slot inward toward the 
reed.  Reducing the tolerances between the reed slot and the reed 
further reduces air leakage and makes for a more responsive reed.  
It can also emphasize every burr and nick in both the slot and the 
reed edges, making centering and offset adjustments more critical.  

> Oh, and is it a common occurance for you to tune a reed that has 
> gone flat, have it sound fine, put the harp back together again, 
> play it - still sounds fine - and then the next day be flat 
> again?  What gives here?

If the reed has just soured a little, tuning it back up should be no 
problem, and should last a while.  If a reed has gone seriously flat 
it's a sign of some kind of stress failure.  You can probably tune 
it back up again, but it's going to fail again rather quickly.  This 
can have a catastrophic effect, like the reed snapping off in your 
mouth.  If the way you're testing the tuning is by playing, it's 
likely not a matter of having sat overnight, but rather is 
coincidentally the next day when you played it again it flatted.  A 
reed like that needs to be replaced.

-tim