Re: Re: Re: [Harp-L] steel reeds

["Vern Smith" <jevern@xxxxxxx>]

----- Original Message ----- 
From: "Tim Moyer" <wmharps@xxxxxxxxxxxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Thursday, March 29, 2007 6:43 AM
Subject: Re: Re: Re: [Harp-L] steel reeds


> I suppose now we need to have a protracted "steel vs. brass" reed
> materials debate.  Maybe Vern could make a pre-emptive strike
> against a difference, sparking a whole slew of emotional posts
> and "me-too" responses, then the "tastes great/less filling"
> arguments...

I think that the theoretical and empirical picture is clear enough that a 
protracted debate will be unnecessary. From my investigation of the 
literature and experience making reeds, here are my conclusions:

Exotic reed materials will not produce exotic sounds. The mechanism of sound 
production is the same provided that the air pressure, frequency, and 
amplitude is also the same.  I was disappointed to discover this.  Some 
materials THEORETICALLY SHOULD be more robust and resist fatigue longer. 
Proving this would require putting a large number of reeds of several 
various materials on an air supply and cycling most of them to failure.

The differences in modulus of elasticity and density among copper-alloy reed 
materials, brass, bronze, BeCu are too slight to perceptibly affect reed 
performance.  BeCu is more brittle, making it more difficult to change reed 
gap without damage.

Stainless steel has a  higher modulus of elasticity and a lower density than 
the copper alloy materials.  That means that a SS reed and a Cu-alloy reed 
having the same pitch and tone will have different shapes.  However, SS 
reeds can be designed to have the same pitch, response, and tone as an 
equivalent Cu-alloy reed.

To design a SS reed to have the same performance as a Cu-alloy reed of the 
same length and pitch, the following must be met:

1. At every cross section where they bend near the rivet, EI of both reeds 
must be the same.  E is the modulus of elasticity of the metal and is higher 
for SS than it is for Cu-alloys.  I is the moment of inertia of the cross 
section which is proportional to the third power of reed thickness.
2. At every cross section near the tip, the mass per unit length must be the 
same.

Thus the SS reed must be a little thinner near the rivet to compensate for 
its higher E and and a lot thicker near the tip to compensate for its lower 
density.  When these conditions are met, there is no difference in reed 
response or tone perceptible to the player or listener.

Some SS reeds have been made of flat stock and then tuned to produce the 
correct pitch.  However, they can have different stiffness compared to the 
equivalent Cu-alloy reed and thus a different response to the player's 
breath pressure.

I have a SS reed in a 270 that so far no one has been able to find by 
playing the harp.

My apologies for providing so much background that the foreground may have 
gone underground.

Vern