Re: [Harp-L] Brass vs Stainless Steel

["Vern Smith" <jevern@xxxxxxx>]

----- Original Message ----- 
From: "Vern Smith" <jevern@xxxxxxx>
To: "Björn Sigurdsson" <bjosi436@xxxxxxxxxxxxxx>
Cc: <harp-l@xxxxxxxxxx>; <jandkday@xxxxxxxxxxx>
Sent: Friday, September 05, 2008 4:06 PM
Subject: Re: [Harp-L] Brass vs Stainless Steel



----- Original Message ----- 
From: Björn Sigurdsson
To: Vern Smith
Cc: jandkday@xxxxxxxxxxx ; harp-l@xxxxxxxxxx
Sent: Friday, September 05, 2008 1:23 PM
Subject: Re: [Harp-L] Brass vs Stainless Steel


> Hi, when talking about that that steel reeds are thinner at the base than 
> brass, I get this idea of a reed that you make considerably thinner on the 
> middle and a bit thinner at the base - so it reminds of lying B in a 
> shape. My idea is: If I blow not so hard just the outer part will vibrate 
> giving me a tone, but when I blow with more pressure the whole reed while 
> start to vibrate, giving me a lower tone while the higher tone is still 
> sounding.

> What do you theory guys think, will it work in theory?

Short answer...no.

Long answer:  Harmonica reeds normally have one mode of vibration.  You are
describing a reed with more than one mode of vibration.  When this happens
in real life, the reed squeals and makes horrible sounds..e.g. certain
overblown Lee Oscar reeds.  Although the steel reed is thinner, the metal is
"stronger" so that the overall stiffness and the behavior of the reed in
vibration is exactly the same an equivalent brass reed.

You cannot just make a reed any shape you choose. There are the design
constraints of width, length, pitch, and stiffness/responsiveness.  There is
also stress distribution.  You want to spread out the bending so that it
does not occur at one thin place and overstress the metal.

Vern
> regards
> Björn Sigurdsson

2008/9/5 Vern Smith <jevern@xxxxxxx>


----- Original Message ----- From: <jandkday@xxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Friday, September 05, 2008 6:32 AM
Subject: [Harp-L] Brass vs Stainless Steel


..... I always thought brass to be a softer metal,

but does it's pliability make it easier to bend?  Stainless steel seems
stronger but is that a
good thing in a harp?   Any engineers want to chime in?  I'm in over my
head.


Definitions:
"Stress" refers to the amount of force (per unit area) applied to a piece of
metal.
"Strain" refers to the stretch (per unit of length) as it deforms.

When you stress a piece of metal, up to a point called the "elastic limit,"
then release it, it will return to its original shape.  Below the elastic
limit,  strain is proportional to stress. The elasticity of a metal is the
ratio of stress divided by strain. Steel has a higher elasticity than brass,
i.e. it takes more force to get a given amount of bending. Some steels have
a stress level (lower than the elastic limit) called the "fatigue limit".
Below that stress, you can exercise the metal for an unlimited number of
cycles without fatigue failure.

If you stress a metal beyond the elastic limit, it enters a plastic zone
where strain is no longer proportional to stress and it will not return to
its original shape.  Its behavior in thiis zone is described by its
ductility.  Ductility is roughly the amount of strain it will take before it
breaks. The opposite of ductility is brittleness. Brass is more ductile than
steel.  Glass is an example of extremely low ductility and gold is an
example of extremely high ductility.

When we change the gap of a reed, we bend it beyond its elastic limit so it
will not return to its original shape but will assume the new gap. Beryllium
copper is a very elastic spring material with high resistance to fatigue.
However, it is very brittle and easy to break when re-gapping.

Because of its higher elasticity, a SS reed will be thinner near the rivet
where it bends than a brass reed of equivalent pitch and responsiveness.
However, because SS is less dense than brass, it will be thicker at the tip
than the equivalent brass reed.  If each is reed is designed to have the
same pitch and responsiveness, there will be no perceptible difference in
tone between reeds of different metals.

Metallurgists may chide me for omitting some exceptions and qualifications.
The rest of you may chide me for getting too technical.

Vern




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--
Björn Sigurdsson
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+46 706 897257


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