Re: [Harp-L] flat, tuning drift, and the 100-plink test

[Winslow Yerxa <winslowyerxa@xxxxxxxxx>]

So what about when a reed changes slightly in pitch but continues to
play for months and even years? Clearly metal fatigue is a long way off
and yet something is causing the pitch to change. So you touch up the
tuning and continue to play it.

One thing I find puzzling is the settling process in tuning. You raise
the pitch of the reed and get it precisely in tune, leave it for
awhile, and it is even higher in pitch (but if you tune it down it
pretty much stays put). Or alternately, you tune a harp just the way
you want it. Then you play it and it sounds great, but the next time
you pick it up the tuning on some notes has drifted by a few cents.

The majority of tuning I do does not seem to involve reeds on the edge
of fatigue. It's a mix of touch-ups, tempering the pitch standard (A442
seems to work best for me) or tempering the notes in the scale to sound
well together, along with the occasional altered tuning.

When I suspect that a reed is on the edge of fatigue, I plink it 100
times in quick succession, raising it a few millimeters each time
before releasing it to vibrate. This only takes about a minute. If the
reed is going to fail, it will very likely fail within the 100 plinks.

Winslow

--- Vern Smith <jevern@xxxxxxx> wrote:

> 
> .----- 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
> 
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