Re: [Harp-L] ...Why do reeds go out?

[David Payne <dave@xxxxxxxxxxxxxxxxxxxxxx>]

I'm pretty sure you meant reeds going out of tune via metal fatigue, but I wanted to add. 
Reeds will also go out of tune for other reasons. You can be playing a harmonica in cold weather and it will go out of tune. That's because all the humidity in your breath turns to water in the cold air and forms droplets inside the harmonica and makes it go out of tune. This is especially true on blow reeds, because water droplets collect on the reed itself. The water wants to run down the reed -although some will stick anyway - but the reed keeps slapping it back up toward the rivet. Most people probably wouldn't notice the drop in pitch, but it's there. 
I've seen reeds go sharp because of an obstruction near the rivet end of the reed - it has to be a solid one that effectively shortens the reed, but that's kind of rare. USually the reed will just sound dead. I did have a stuck mustache hair change a reed's pitch this way a few times.   
I've seen gunk drop a reed in pitch. I had one come in a while back for a several reed replacements. It was out all over the place, especially the blow reeds. When I took off the blow plate, there was all this extreme nastiness inside, it wasn't just regular nastiness, it was of Biblical proportions with a big, thick strip of green nastiness near the rivet end of the reeds (it's hard for stuff to collect on the free end because it moves so much). Turns out after cleaning, only one reed needed replaced. I suspect sugar was involved to glue bits of food inside. Sugar is like cement inside a harmonica. It will lock up a chromatic slide like super glue, although that was probably the first time I noticed sugar being detrimental to a diatonic. Think about that before you down a six pack of Bubba cola while playing your favorite harp ;)
 
David Payne
www.elkriverharmonicas.com


Elk River Harmonicas Forum now available via Iphone app, www.elkriverharmonicas.com/forum


________________________________
 From: David Payne <dave@xxxxxxxxxxxxxxxxxxxxxx>
To: Harp L Harp L <harp-l@xxxxxxxxxx> 
Sent: Saturday, May 19, 2012 6:10 PM
Subject: Re: [Harp-L] ...Why do reeds go out?
 

Take a paper clip. Bend it back and forth until it breaks. That's what happens. It starts with a little crack. When it cracks, the reed drops in pitch. That crack always starts in a milling mark near the rivet end, wherever force is most concentrated. There is a lot of force involved. When the reed swings one way, it is under tension force. When it swings the other way, it is under compression force. Both these forces are strongest on the outside surface of the reed. For example, let's take a reed that is swinging outside the harmonica. Let's stop it there and look what happens. The back of the reed (the one facing the inside of the harmonica) is under tension force. The side of the reed facing outside is under compression force. These two forces are opposite, so as you go deeper inside the reed - let's say from the outside - the compression force decreases. Then you get to a point where there is neither compression or tension force... kind of a force
 purgatory. go deeper, you start seeing tension force, which increases until you come out the back of the reed. 
The milled side is the weakest, so it's going to crack there.  

OK, so both these forces are strongest on the outside of the metal. A crack will appear on the surface of the reed. This crack is shallow (remember that as you go inside the reed, force decreases until you get to a point where there is no force). As you play, the crack gets longer (but not necessarily deeper) until it has gone all the way across the reed. As it does this, the pitch gets flatter. An interesting thing happens once the crack goes all the way across. The surface of the reed moves deeper. That is, the place where the force is concentrated moves deeper inside the reed as the crack gets deeper. Once that crack has moved all the way across, you have a significant defect in the structure. Now, the reed is thinner where the crack is, while the rest of the reed is much thicker. Thus, more and more force is concentrated at the location of the crack. This is why a reed will fall slowly out of tune, but then one day it's done. 

Back in the 1930s, when a harmonica employed by Borrah Minnevitch's Harmonica Rascals started going out of tune, Leo Friedman would coat the reed with a very thin coat of solder, retune the reed and it would last them until they could get a replacement reed. What he was doing was filling in this crack at the first inkling the reed was going south, distributing the force over a wider area. 
 
David Payne
www.elkriverharmonicas.com


Elk River Harmonicas Forum now available via Iphone app, www.elkriverharmonicas.com/forum