Re: [Harp-L] RE: Fatigue and Reed Life: An Objective Test?

["Vern Smith" <jevern@xxxxxxx>]

----- Original Message ----- 
From: "Joe and Cass Leone" <leone@xxxxxxxx>
To: "Vern Smith" <jevern@xxxxxxx>
Cc: <harp-l@xxxxxxxxxx>
Sent: Saturday, April 19, 2008 10:31 PM
Subject: Re: [Harp-L] RE: Fatigue and Reed Life: An Objective Test?


> > Changing only the width of a reed does not change its pitch.

> No, but could it make it stronger.

No. The stresses arise from the radius of curvature of the reed.  Since two 
narrow reeds or one wide one all have the same curvature at any instant, 
they have the same stresses and the same tendency to fatigue.

Wide reeds are less likely to squeal by vibrating in a twisting mode.

> That's what 'I' thought. I thought that the reed would sound with  less 
> breath if the profile was changed WITHOUT making the reed so  thin as to 
> be almost 'foil' like (and weak).

> Why would I find it difficult to believe. What I was trying to say  was 
> that I felt that making the reed narrower but thicker might  produce the 
> same tone as the amount of unsprung weight would be the  same. But since 
> the metal was now in thickness (instead of width),  the reed would be 
> strong enough to handle the strain better.

It depends on what part of the reed you make thicker.  We know from tuning 
that making the reed thicker at the tip lowers the pitch and that making it 
thicker near the rivet raises pitch.  You could add thickness near the rivet 
which would raise pitch.  Then you could add thickness at the tip to bring 
pitch back down to the starting point.  That would result in a thicker reed 
overall.  However you would not like the result because you would have to 
blow a lot harder.  The reed would be very unresponsive.

Actually, a thinner reed where it bends near the rivet would be "stronger" 
in the sense that the stresses in the metal would be lower for a given tip 
deflection. If you made the reed thin near the rivet it would lower the 
pitch.  Then you would have to make the tip thinner to return the pitch to 
the starting point.  You would have an overall thinner reed that would 
probably last longer.  However, you would not like that either because it 
would sound weak and choke  & squeal easily.

A well-designed reed has a delicate balance among stiffness (thickness near 
the rivet); tip mass (thickness near the tip): length, stress distribution 
(thickness profile or taper); and elasticity and density of the metal. 
Because they are are all inter-related, you cannot just change one thing 
without changing others to compensate. Because pitch must be held absolutely 
constant, changes will affect responsiveness. Sadly, there ain't no free 
lunch.


> Much the same as I feel that reeds  should be polished smooth with NO 
> milling striations NOR any tuning  gouges. Tuning should be 'buffed' in, 
> leaving a gradual  infinitesimally shallow scooping.

I agree completely.  That is why I prefer Shofu Brownie (fine abrasive in a 
rubber matrix) wheels for tuning. However, polishing when you don't need to 
tune will change the design of the reed.

> ...... But as it sits right now, I feel  that the reeds are the weak point 
> of a harp (setting jet engine  breathers aside), and while they were never 
> intended to tolerate the  abuse that they take THESE days, still some 
> improvements could be made.

I think that Seydel is on the right track with SS reeds.

Do you think that valves rival reeds as weak points?

> Another thought of mine was to install pressure reliefs into harps to 
> prevent turbine breathers from exceeding their designed operating 
> pressure.

You would have to have one for each reed because there is no common air 
chest (but your own) in a harmonica. Where would you put them all?  I 
suspect that that relief valves in an accordian are there more to protect 
the bellows than to protect the reeds.

Vern
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