harpdude61
779 posts
Mar 17, 2011
7:03 AM
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Since we've had a couple of good threads on overbends lately I'll bring up a question I have pertaining to overbend physics. Maybe some of you customizers or pro players know. I have a natural curiosity of how the harmonica does what it does.
I understand that draw bends and blow bends are possible because of the two reeds of the hole working together. You can bend from the higher pitch down close to the lower pitch.
With overblows the blow reed stops and the draw reed sounds. ..with overdraws the draw reed stops and the blow reed sounds.
My question is...what is actually happening when you bend an overbend? Does the other reed come back into play? That doesn't seem possible....or are you changing the shape of the reed in some way?..are you using less of the reed? I've never heard this discussed.
Thanks for answers and/or speculation.
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MrVerylongusername
1615 posts
Mar 17, 2011
8:03 AM
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Very interesting question. I wish I could answer it! If anyone knows a definitive answer I'd love to hear it.
Here's my speculation:
Normally there is sympathetic vibration of one reed upon another
With the partner reed eliminated from the equation (it is choked) the reed is resonating with the throat and mouth alone; not with it's partner reed.
Since the airflow rate can be constant - you don't overblow by blowing harder - I can only presume the change in pitch is about a shift in the point at which the reed flexes (as a result of harmonising with the resonant frequency of the mouth). That might help to explain why longer thinner reeds are better for overblows too.
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HarpNinja
1224 posts
Mar 17, 2011
8:08 AM
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Aren't there some vids that show this? I think I saw them on the forum at one time.
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Mike
Quicksilver Custom Harmonicas
Updated 3/14/11
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harpdude61
780 posts
Mar 17, 2011
8:51 AM
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You may be right Mr. Very.....I know that sometimes it sounds like the overbend bends up a step and a half, so the reed must be getting shorter.
Ninja....I remember those but not sure if they showed bending an OB. I can't find them.
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MrVerylongusername
1617 posts
Mar 17, 2011
9:00 AM
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I think they were by GermanHarpist if it's the ones I'm thinking of.
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nacoran
3897 posts
Mar 17, 2011
9:22 AM
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I think Turboharp.com has some x-ray photos of bending. I've seen some strobe pics on YouTube too.
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Nate
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sorin
264 posts
Mar 17, 2011
9:36 AM
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I think the overbends are just a single reed bends .When you overblow the 6 hole the 6 draw reed bends inward , toward the blow plate , inside the the slot , making the reed shorter . There is no interaction between the reeds in the same hole ( like in a regular bend) and its very easy to prove by taking the covers off , blocking the 6 blow reed , and you will see that you can still overblow and bend it up , actually it makes it much easier.
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HarpNinja
1226 posts
Mar 17, 2011
9:43 AM
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I think sorin is right, but I don't have a way to double check right now.
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Mike
Quicksilver Custom Harmonicas
Updated 3/17/11
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MrVerylongusername
1618 posts
Mar 17, 2011
10:29 AM
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Yes, that explains the mechanics of overblows, but it doesn't explain what happens when you bend an overblow which was the original question.
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HarpNinja
1228 posts
Mar 17, 2011
10:59 AM
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It does explain it. The one reed moves for the ob...when you bend the ob, it moves differently and created the pitch shift.
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Mike
Quicksilver Custom Harmonicas
Updated 3/17/11
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MrVerylongusername
1619 posts
Mar 17, 2011
11:03 AM
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What mechanism makes the reed move differently?
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HarpNinja
1229 posts
Mar 17, 2011
11:10 AM
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The direction of the air flow....just like any other bend. I guess the air hits the blow reed, which is closed (so it is like hitting a wall) and that makes the draw reed move. As you change the angle of the air coming it, it changes how it reflects off the blow plate.
At least that is my guess...and it make sense with how a good ob'ing harp works...I think your previous point probably nails it.
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Mike
Quicksilver Custom Harmonicas
Updated 3/17/11
Last Edited by on Mar 17, 2011 11:11 AM
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MrVerylongusername
1620 posts
Mar 17, 2011
11:32 AM
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Ah, OK, so changing the angle of airflow effect the force acting on the reed tip - would that change the flex point? I can't see it would, but I can see it altering the frequency of the reed vibration, which would be the only other way to change pitch if the flex point stays constant.
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mrdon46
65 posts
Mar 17, 2011
10:51 PM
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The physics of bending an overbend? That's getting into the realm of quantum mechanics--and I'm no Einstein.
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Milsson
13 posts
Mar 18, 2011
3:27 AM
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I'm shure it has to do with resonance. When the frequency in the mouth cavity matches the blow reed it stops vibrating, aka chokes, and the draw reed can "popp".
This is just my own opinion but it could be true.
Further reading:
http://www.motorcycle.com/how-to/how-twostroke-expansion-chambers-work-and-why-you-should-care-3423.html
http://en.m.wikipedia.org/wiki/Acoustic_resonance
Edit: oooops.. I missed the real question. I think the one reed bending has to do with air velocity.. Think of blowing on a straw between your thumbs. The "faster" wind flow alters the pich.
Last Edited by on Mar 18, 2011 3:35 AM
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Andy Ley
87 posts
Mar 18, 2011
5:43 AM
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I believe Jon Gindick espouses practicing your first overblows by removing the coverplates and physically blocking the blow reed with your finger.
In answer to the OP, I guess the way to check would be to block the reed and see if you can still bend the OB.
I would attempt this, but overblows are still giving me the Foxtrot Oscar.
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MrVerylongusername
1625 posts
Mar 18, 2011
6:30 AM
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@Milsson
You don't necessarily blow harder to change the pitch of the overblow, although I like HarpNinja's idea that the angle of reflection alters the velocity. That does seem to fit with my experience of bending overblows, which is more about the mouth shape and direction of the airstream.
@Andy Ley
You can still bend the overblow if the other reed is blocked - I don't think the paired reed has anything to do with this sort of bend. That in itself is interesting, normally a bend is limited by the interval between the pitches. The only things that seem to limit the overblow bend is the skill of the performer, the stability of the reed and the degree to which the blow reed stays choked.
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Andy Ley
88 posts
Mar 18, 2011
6:48 AM
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@MVLUN
Thanks. I will file that tidbit away under "things to concentrate on when I can actually play"! I'm still trying to get my standard bends to some semblance of accuarcy. As for overbending, I can choke and squeal, but no note yet. I'm happy to ignore bending an over bend for the time-being :)
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nacoran
3905 posts
Mar 18, 2011
8:20 AM
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There are some good articles on how accordions work inside, though I don't have the bookmark handy. They are fairly high on Google rankings. They might be useful on the subject of what is going on with the reeds.
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Nate
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harpdude61
781 posts
Mar 18, 2011
8:32 AM
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Mr. Very...you bring up a good point. Bends are limited to the pitches between the two notes of the hole. Overbend bends are infinite in a sense of speaking.
The skill of the player, harp set-up and type of reed affect this I'm sure. I have a couple of old harps that I've tinkered with and I can get the overblow to bend up two full steps.
I relate it to hanging 6 inches of a ruler over the end of a table and plinking it to get a pitch. The less ruler hanging over the edge, the higher the pitch...but , there comes a point to which the effort it takes to make the ruler vibrate is greater than the strenth of its structure and it breaks.
How far can we go with a harp reed?
I know bending up a 1/2 step or maybe a whole step may be useful. Beyond that probably does not sound good. Still an interesting subject. WOuld it be possible to make a one hole harmonica with one reed that can be overbent and play maybe an octave?
Last Edited by on Mar 18, 2011 8:33 AM
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GermanHarpist
1967 posts
Mar 18, 2011
9:56 AM
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As far I think it goes like this...
The pitch and ease at which the reed vibrates is determined by the resonance chamber in your mouth. If you change your mouth resonance the reed is willing to follow to a certain extend (depending on resonance and airflow control).
Bending implies that it alters from the 'optimal' harmonic resonance (at which the reed vibrates the strongest) and thus the strain on the reed is reduced.
It is important to distinguish between a reed being played inwards like it was supposed to be or played backwards/outwards as the blow reed when draw bending and the draw reed when overblowing.
When the bent reed is pushed into the slot at a certain moment it simply gets stuck because of the airflow push.
When the reed is pushed outside of the slot something like this can't happen. As long as you can apply enough resonance force on this reed it will continue vibrating. However, also here you have to fight against the air stream which wants to hinder the vibration by pushing in one direction.
Luckily, when pushed outside of the slot (although this is not the way it was 'supposed' to be played) the reed actually plays louder as it is forced by the air stream to alternate wider. This is beneficial for the strong bends on hole 2 and 4 because it gives the reed a very prominent and slightly distorted sound. This is also quite useful for overblowing because you can easily bend up the note but still have the necessary volume.
However the reed was not dimensioned for this kind of vibration and will break when overstressed. In general it needs a rather soft and steady controlled airflow to play the outward vibration well.
For all regular bends it is necessary for the inwards played reed to be a little further away to bend nicely. And the outward bend reeds to be a little closer.
For the overblows the inward played reed needs to be gapped closely so that it blocks easily and the outwards should be gapped closer so that it bends higher.
Gapping is always a trade off between gapping for ob/bends and gapping for normal attack.
Embossing basically helps with any kind of vibration so it is beneficial for all bends and overblows to play easier.
This did not directly answer harpdudes question, but I hope it is of help anyway.
Last Edited by on Mar 18, 2011 5:53 PM
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harpdude61
784 posts
Mar 18, 2011
2:31 PM
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GermanHarpist..Excellent answer! I had not visualized what the reed would look like taking its vibration source form the opposite side of the rivet.
Great response and I agree with it all except one thing....I beleieve you can gap the reeds for maximum play of all overbends available and still attack the harp to get any type of dynamics or style you want to play. To me, the key is learning to play at a low volume and totally relaxed. Let the amp take care of the volume and I think overbends come easier if you play them softly and the reeds do not stick when you try to blend in other styles.
Last Edited by on Mar 18, 2011 2:32 PM
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