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




----- 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
Visit my harmonica website www.Hands-Free-Chromatic.7p.com







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