Maraboy
71 posts
Dec 16, 2018
7:30 AM
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Can anyone wise guy tell me what physical phenomenon is behind the bending? So how does the blow reed participate in the phenomenon? Why the draw reed can be bend only if the tuning of the blow reed is lower than the tuning of the draw reed? And why the bending can’t go lower than the tuning of the blow reed? If the blow reed is stuck and does not move at all, the draw reed can’t be bend at all. Why?
If you can’t explain this, write something “good question” so that you help to keep my question on the first page as long as someone can give a good explanation of this phenomenon, Mara
(I hope that you understand my Finglish (Finnish –English)
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The Iceman
3736 posts
Dec 16, 2018
12:20 PM
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Try to find a copy of "The Harp Handbook" by Steve Baker. You may have all your questions answered there.
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The Iceman
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MindTheGap
2583 posts
Dec 17, 2018
1:06 AM
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Maraboy, I wouldn't go any further with this if I were you. As a physicist I wanted to know why too - it's such an unusual and interesting thing.
I looked around and I found some scientific papers on the subject, they've been refenced a number of times of this forum. But they typically only explain the circumstances you need to make it happen rather than the fundamental reasons. Interesting though: MRI scans, lab mock-ups with syringes and tubes, hi-speed film etc.
The basic idea put forward is that you alter your resonant cavities in the vocal tract, just like for speaking and singing, and somehow the two reeds respond to pick up a frequency from that. For a single reed bend that seems fair enough. But why and how the two reads couple - I've not seen an explanation of that beyond that they do.
I need to add that I've heard some weird and wonderful ideas put forward too, by harmonica players :) The vocal tract is a pretty well understood thing as it's been researched for speech and singing, but some people like to invoke other physical principles - not sure why that is.
It's also popular to liken a harp reed to a guitar string (harmonics, standing waves and all that) which looks clearly wrong from the physics, high speed photography and the sound output! My guess is that harp players often play guitar, so why not? :)
You might start simpler by asking how does a single harp reed vibrate at all when you blow air over it, and how it produces sound? Again, wacky common sense based theories abound! But that one is known (properly) I believe.
Last Edited by MindTheGap on Dec 17, 2018 1:19 AM
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Littoral
1648 posts
Dec 17, 2018
4:12 AM
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My version, and backed up by much of what MindTheGap references in the available research (which I've fussed over for years). It's basically an advanced whistle that can shape air flow. Think of the pitch that occurs blowing across the top of a bottle, which is also a whistle. There is a specific frequency possible because of the shape of the bottle and air blowing across the top. The two reeds in a harp function together to make the shape of the airflow moveable. The reeds are not making the sound.
Now, why the physics of the diatonic design allow for the fundamental notes to be so accessible can only be explained by super natural powers. I've never seen any evidence that shows the bends were intentional in the design - much less allowing for the chromatic scale. Which brings us to overblows, in case you thought the supernatural part was a joke. We all know they only happen with some bonafide faith. Just like Santa and Mel Tormes Christmas Song. It's all there, you just have to believe.
Last Edited by Littoral on Dec 17, 2018 4:12 AM
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MindTheGap
2584 posts
Dec 17, 2018
4:47 AM
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I don't think the harp is classed as a whistle, but it's similar territory in that it's an air-flow instability thing going on. The same thing that makes wires sing in the wind.
It's a complicated business, but even without understanding the detail it seems clear that the reeds themselves aren't making much sound. When you ping a guitar string it sounds like a guitar, when you ping a harp reed it doesn't sound much like a harp. Which points the finger at the air chopping about.
This doesn't answer the OP though - the double reed issue.
Last Edited by MindTheGap on Dec 17, 2018 4:49 AM
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Littoral
1649 posts
Dec 17, 2018
5:47 AM
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The two reeds both move (on bends) to shape the air flow- like a double sided whistle in which we can control the shape. We could add a lot of details on pressure differences but the principle would still be a lot like what happens with a whistle. Understanding what happens with a whistle, like a bottle, is pretty easy. That's why I like the comparison to a whistle.
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MindTheGap
2585 posts
Dec 17, 2018
6:08 AM
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Actually a whistle? OK then :)
EDIT: ah, the penny dropped, you're pulling my chain. Ok you can have that one as it's nearly Christmas :) But actually the physics of whistles is relevant, as I say.
...but now I'm thinking were all the other long discussions I had on here a wind up too? d'Oh!
Last Edited by MindTheGap on Dec 17, 2018 6:16 AM
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dkrulewich
18 posts
Dec 17, 2018
9:10 AM
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As a fellow physicist and mathematician by education, I really enjoyed this discussion. I passed on the opportunity to put in my two cents. Although I've read explanations, they've either been too simple or too complicated.
In the end, it might make no difference to playing technique. You just try things out, until something works. I sometimes visualize my entire airflow tract down to the diaphragm as an organ tube, through which I can only adjust pressure and speed of the air. No attempt here to explain what role reed interaction plays.
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dchurch
213 posts
Dec 17, 2018
1:25 PM
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I don’t know how this “fact” that it takes 2 reeds to create a bend was accepted. But that is simply not true.
I made a weird experimental practice harp a few weeks ago. It just took a little bit of me learning to adjust to it. I’m draw bending the 1, 2, and 3 just fine. And it ONLY has draw reeds in those holes. The blow slots are totally blocked off!
If you have something like a “French Tuner” you can try it yourself, or tape off the holes… Just understand it takes a delicate touch and a few minutes of practice.
That leads me to believe that bending has more to do with the physics of precise air flow and altering air pressure within a resonant air chamber (air pressure within the aforementioned bottle).
We may have learned to create a precisely controlled airplane wing at a choke point in the bottom of the chamber. I think the theory is backed up by the fact that it not easy to develop the bending technique.
Here’s another air pressure theory test. Draw a deep sustained 3 hole bend using a pucker technique. Then let a marginal amount of air leak between your mouth and the harp. You should be able to draw the 3 note without a problem but the bend is instantly lost with the change in your resonant air chamber pressure.
I am not trying to fully explain bending so much as just offering something to consider about the subject.
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It's about time I got around to this.
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dkrulewich
20 posts
Dec 17, 2018
1:57 PM
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Mathematicians and Physicists admit they don't fully understand even the model of fluid flow given by Navier-Stokes. Million dollar prize for complete rigorous solutions is still offered.
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MindTheGap
2586 posts
Dec 17, 2018
2:05 PM
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The observation that you need a good seal to get those bends, and you don't to get an unbent note, always made me think that air pressure or some characteristic of the flow ought to be involved.
That doesn't go down well with those who believe that resonance in the vocal tract is responsible for everything. I don't know why they believe it - it doesn't strike me as a matter for faith - but they do.
It's true that you don't have to have two reeds to make a bend, but there definitely is a two-reed bend phenomenon which has different features to a single reed bend.
Certainly you don't need to understand it to play it, and if visualising your throat as an organ pipe gets a better sound then job done. It would seem reasonable that doing the same things that make your singing voice better could make your harp sound better too. Probably some people have a naturally better sound.
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Maraboy
72 posts
Dec 18, 2018
12:08 AM
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Thank you very much for interesting thoughts. I put the same question on MBH Facebook and I thought I should accept this:
Patrick Byrnes Authoritative studies indicate that it involves selling one's soul to Old Scratch.
Then I got the link (it is down there) to a research summary (14 pages), and I have come to the conclusion that in full bend it is really the blow reed which make the sound like in the overblow it is the drew reed which make the sound. So from a study in a nutshell:
Referencing hole 4 on a C Harmonica, the draw note sounds at the pitch D. As the constriction point moves back in the mouth, the pitch of the anterior chamber is lowered and the D note lowers in pitch. The blow reed is tuned to C, which is a whole step lower than the draw reed. As the bending process lowers the D note of the draw reed, the C reed starts to get excited and vibrates. As the pitch-lowering process continues, pitch production transfers almost entirely to the blow reed, to the point that if you were to take the cover plate off the draw reed side of your harmonica, you could place your finger on the D draw reed when in the full bend and the bent note will continue to sound.
Leif Motsch Knudsen Maybe this: https://www.bluesharmonica.com/sites/bluesharmonica.com/files/mri_bending_study_barrett.pdf?fbclid=IwAR0pbCd5zY93XWRvEttU7ofcaElyFLrWcObfewxFydAiRAS6PoQEdyYz9i8
And I disagree with dchurch: “I don’t know how this “fact” that it takes 2 reeds to create a bend was accepted. But that is simply not true.” Namely, the whole question came in to my mind when I wondered how to build a harmonica where all the draw reeds can be bent. I built a harmonica where the blow reed plate was a solid metal plate. Then the draw reeds I was able to bend very little or not at all, mara.
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MindTheGap
2587 posts
Dec 18, 2018
2:47 AM
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Maraboy - thanks, although this is just another observation what the reeds do during the two-reed bend. Not an explanation of why. But if that answers your OP question, that's fine.
The deeper question is what is the pitch-lowering process? The prevalent explanation seems to be something like that the vocal tract makes a resonant frequency and the two reeds are bound to follow that note. Which doesn't really add up as enough of an explanation: a single reed doesn't feel compelled to do it in the same way, so what's special about two reeds?
A single reed played in its normal mode (not OB) has a resonant frequency based on its shape, weight etc. Like all resonant systems, you can make it vibrate at a different frequency if you force it. That seems consistent with the feel of playing a single-reed. It's easy to make it vibrate at its natural frequency (e.g. hold it in the wind) With effort you can bend it a bit and the note gets weaker as you move away from the normal note.
Last Edited by MindTheGap on Dec 18, 2018 3:00 AM
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mx
37 posts
Dec 18, 2018
10:50 AM
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hi all, the thing I find COOL is when the drew weed stalls out and stops moving the blow reed vibrates backwards ( instead of moving up and down the reed moves down and up ) to the direction of air flow.
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Littoral
1650 posts
Dec 18, 2018
12:22 PM
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Does it help to realize that the reed isn't what we hear? Some of the mystery seems implied by an idea that reed vibration is what we hear. It still seems easier to me to think of the shape of the air flow changing (due to the reeds interacting). Optimizing those conditions (reed work) allows for better control of the air flow.
mx - I find that part cool too. That, and the fact the no one actually designed the harp to do it. Serious serendipity.
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SuperBee
5683 posts
Dec 18, 2018
6:53 PM
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"the reed isn't what we hear"
does this influence how people think about the topic of reed material as an influence on tone?
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Littoral
1651 posts
Dec 19, 2018
8:07 AM
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"...does this influence how people think about the topic of reed material as an influence on tone?"
Yes
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WinslowYerxa
1621 posts
Dec 19, 2018
10:27 AM
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By way of supporting the correction stated that bending does not require two reeds, here's a link to a brief recording I made of bending a blow note down three semitones on a chromatic harmonica. Chromatics isolate each reed so that airflow goes only to that reed, so a two-reed bend is by definition impossible in most holes(I did it on two different instruments, though I no longer remember which two.)
===========
Winslow
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Last Edited by WinslowYerxa on Dec 19, 2018 10:28 AM
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Tom585
84 posts
Dec 19, 2018
10:20 PM
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Is there a moment in the bend on the diatonic when both the draw and blow reeds are vibrating at the same time?
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JSalow
48 posts
Dec 20, 2018
11:10 AM
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"Does it help to realize that the reed isn't what we hear?"
This is a meaningless distinction. Yes, that's how sound works. When you hear a guitar, you're not "hearing" the strings, you're hearing the air movement caused by them. Same with every sound in existence. That doesn't change the fact that it is the specific way in which materials vibrate that affects the way the air moves and therefore the sound (timbre). So yes, for all practical purposes you are "hearing" the reed in the same way you hear anything else.
Last Edited by JSalow on Dec 20, 2018 11:11 AM
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Littoral
1652 posts
Dec 20, 2018
11:45 AM
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JSalow ,
"This is a meaningless distinction."
To you, which is why I asked IF it helped to realize that the reed isn't what we hear. It's clear from some statements that are made that a lot of people DON'T actually realize the reed isn't what we hear. Making that distinction, and trying to describe what we do hear, was an attempt to help make better sense of the interaction between the two reeds - which was the topic of the OP.
Maybe you could actually add something meaningful?
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MindTheGap
2588 posts
Dec 20, 2018
1:08 PM
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Last Edited by MindTheGap on Dec 20, 2018 1:35 PM
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