Fw: [Harp-L] Retuning reeds




----- Original Message ----- From: "Vern Smith" <jevern@xxxxxxx>
To: "Aongus MacCana" <amaccana@xxxxxxxxxx>
Sent: Monday, March 23, 2009 11:01 AM
Subject: Re: [Harp-L] Retuning reeds




----- Original Message ----- From: "Aongus MacCana" <amaccana@xxxxxxxxxx>
To: <robertpcoble@xxxxxxxxxxx>
Cc: "Harp-L List" <harp-l@xxxxxxxxxx>
Sent: Monday, March 23, 2009 10:05 AM
Subject: [Harp-L] Retuning reeds



....................Lowering the pitch of a reed by filing or chiseling the root seems like a
bad idea to me as it introduces a stress raiser at the most highly stressed
part of the reed and must surely shorten the reed's life.
Beannachtaí
Aongus Mac Cana


I disagree for the following reasons:

IF the excavation is spread out and tapered over about a
third of the length of the reed , there is no reason for
there to be a stress raiser.  With all but the most skilled
and careful of technicians, that is admittedly a big IF!

However....let us assume that you lower the pitch of two
identical reeds, one by weighting and one by thinning.
Assume that both vibrate at the same frequency and amplitude
and have about the same curvature at the extremes of motion.
Because the stress in the metal fibers at the surface is
proportional to thickness, it is arguable that the stress
in the thinner reed is actually less! Because the air
pressure required is less for the thinner reed, it might be
slightly less loud. Because human hearing is logarithmic,
the difference in loudness might be imperceptible.


Although impractical, the ideal way to lower the pitch of a
reed would be to increase its length.  Then at the same tip
amplitude, its curvature and thus its stress would be less.

When lowering the pitch of a reed by removing material near
the rivet, think about minimizing its curvature at the top
and bottom of its swing.  If you remove all the material in
one area, most of the bending will occur there, the
curvature will be high, and so will the stress.

Vern





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