Re: [Harp-L] flat

["Vern Smith" <jevern@xxxxxxx>]

.----- Original Message ----- 
From: "michael hines" <otisharp@xxxxxxxxxxxxx>
To: <Harp-L@xxxxxxxxxx>
Sent: Saturday, December 01, 2007 11:31 AM
Subject: [Harp-L] flat


> What actually causes a reed to go flat? Does it lose temper, or is it gunk 
> on the reed or a combination? Sounds like a dumb question, but i never 
> really thought about it before and now i have one.
>
> Mike

Copper alloys (Brass/bronze) cannot be "tempered" like steel.  Heating and 
cooling steel at various rates can affect the dissolved carbon and greatly 
change its properties.  Brass/bronze for reeds is cold-rolled to work-harden 
it by breaking the metal crystals into smaller ones.

Reeds usually go flat because the metal fatigues near the rivet where 
bending is greatest.  Microscopic cracks develop along the boundaries of the 
metal crystals or grains and gradually get larger and join to make bigger 
cracks.  If  a reed goes flat, you tune it up, and it soon goes flat again; 
that is a symptom of metal fatigue.  The only remedy is to replace the reed. 
Fatigue can occur when you are blowing/drawing hard for a long time...many 
millions of cycles of vibration at a high stress level in the metal.   I 
believe that steel reeds would be less likely to fatigue than brass/bronze 
ones.

Gunk on a reed is much more likely to glue it shut so it won't sound at all. 
Removing the gunk will remedy the problem.  A piece of gunk big enough to 
flatten the pitch perceptibly would be visible.  A piece of gunk in the 
clearance between the reed and the slot will be visible when you back-light 
the reed and view it straight-on with one eye.

Vern