Re: [Harp-L] Repair problem Mystery?

[David Payne <dave@xxxxxxxxxxxxxxxxxxxxxx>]

First, you all know how much air it takes to set a reed vibrating. Unless a wormhole in time and space has opened up inside the harmonica, it is impossible for air to flow like that. A leak would just leak out into the atmosphere. You know that trick where you cup your hands around a harmonica REALLY tight, blow the 10 and you get the draw reeds going? You know how TIGHT you gotta get the seal to make that happen? That's the concept you guys are describing with the air leak, it ain't gonna happen. But, with the loss of any other explanation, you're stuck with that theory. So was I, until I started studying it.
Next suspect: harmonic resonance. If you've tuned a guitar, you may notice that once you hit the lower string (fretted on the appropriate fret for tuning the next higher string) when it is all in tune, the energy of the plucked string will make the next string vibrate. I first thought maybe harmonic resonance was at work. So, I tried tuning the affected reeds to see what happened. I was tuning them like whole steps or more apart from where the were (and also the other direction) and noticed NO change whatsoever, thus ruling out harmonic resonance.Â
This leaves just one possibility - what you've got is the Tesla Effect, it's mechanical resonance, which was further confirmed to me by the fact that the longer I blew those notes, the stronger the vibration in the other reed became. It was like this feedback loop... like pushing a kid on a swing, you apply the same amount of force throughout, but the kid goes higher and higher. You both mention this happening on plastic comb harps. It happened to me with wood.. so it's not related to any of that, but as I remember, it only happened with the coverplates on. I would be interested whether your examples were changed by addition or removal of coverplates. Very interested.
This link explains the theory of what I am talking about:
http://en.wikipedia.org/wiki/Mechanical_resonanceÂ;

if you watch this episode of mythbusters, you can see where they took a 6 pound machine, based on Tesla's designs, and were able to shake a large steel-frame bridge with a 6 pound machine using mechanical resonance on Tesla's earthquake-machine principle. When they first try it out, nothing happens, but as they dial the frequency of the oscillations in to match the mechanical resonance of the bridge, the bridge starts to vibrate.. when they tune it in, the whole bridge shakes that part is about 21:30 into the episode. They never got Tesla's legendary/mythical earthquake, but their results shook them up.
http://www.youtube.com/watch?v=jUy2HYoUd6MÂ;

Like I said earlier, I mostly tried to make the effect worse, so I could study it and I'm not an engineer or anything, plus I've long since lost track of the harps that did it. So, for actually getting rid of it, I've not devoted a lot of effort to that, but from what little I did do, I think changing gaps and curvature, and making sure the reedplates are on and torqued correctly could make a difference if it's not bad. Changing pitch has NO effect whatsoever. It seems ultimately that changing the mechanical resonance of the reedplates would help. If I had one here doing it now, I would try stuff like adding a strip of brass to the outside of the reedplate... or adding a line of solder or shortening one reedplate slightly. ÂMaybe distribution of weight would change the mechanical resonance. Maybe somebody who knows more about mechanical resonance would have a better idea. The fine details of this are out of my league at the moment.

This whole mechanical resonance experience had me develop another theory a few years back, but it's pretty controversial. As soon as I mention it, it'll kill this thread's subject and will go off into something else. I'll try to remember to post that one later.

On the addition of the sound vents on that one, I'd be interested to know what happened. Side vents don't work by letting sound out, they change tone by letting air in and air flows into the reedslot in different ways Âand directions as a result. Maybe it would also change the mechanical resonance, maybe not. I would be interested to know this.Â

David
www.elkriverharmonicas.comÂ



________________________________
 From: "burket@xxxxxxx" <burket@xxxxxxx>
To: harp-l@xxxxxxxxxx 
Sent: Friday, April 13, 2012 12:35 AM
Subject: Re: [Harp-L] Repair problem Mystery?
 

I had a similar issue a while ago after doing some modifications to one of my old Golden Melodies. It was if when blowing with some energy in 4.5.6.7 holes, solo or in combo, the (resonance ?) as Dave mentioned was traveling down the harp making the 2 blow note make a soft sound.  I thought it was an air issue or leak somewhere in the plastic comb since its a bit old and worse for the wear. I recently made some side vents on that harp's covers so I'll check again if its still there.

I look forward to hearing Dave's take on it. 

Burke T.



Message: 5
Date: Thu, 12 Apr 2012 14:28:46 -0700 (PDT)
From: David Payne <dave@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Harp-L] Repair problem Mystery?
To: Harp L Harp L <harp-l@xxxxxxxxxx>
Message-ID:
ÂÂÂ <1334266126.7480.YahooMailNeo@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset=utf-8

This has nothing to do with air circulation. Nothing at all. I'll explain in 
more detail later, but I'm on my way out to Power Park for the WV Power opener. 
It's resonance and vibration. I've seen it before.ïï

David
www.elkriverharmonicas.comïï