Can someone shed some light on what actually happens to the reeds when a player bends a note? Or point me to a good source?
Let's say the four draw hole is an "A". I understand that by changing embouchure, the draw reed "bends" and pitch lowers and then the blow note starts to vibrate at a higher pitch than its normal pitch, in this case "G". But what is actually physically happening to the reed that makes the draw reed vibrate slower and then stop sounding and the blow reed vibrate faster?
And I find fascinating that it sounds completely seamless! Why?!!
As a player, it isn't necessary to understand this. But I'm teaching a couple of college classes about the harmonica that include engineering, computing and design students who ask! I can only explain so far.
"More specifically, the first semitone, draw bend of hole 3 ~B flat on a C harp is produced primarily from the draw reed. The second semitone, A, can be produced from either reed alone and is most easily produced by both together. The third semitone bend, A flat, comes from the lower pitched blow reed. Similar reed function is found in holes two and ten where the notes are three semitones apart. (In hole 10 the bend is a blow bend)"
The draw reed might start bending down one semi-tone, to be "joined" sympathetically by the blow reed at some blending point in the next semi-tone, where both reeds sound together. At the point the blow reed is modulated upward more than a semi-tone. Then the draw reed gradually tapers off leaving the blow reed to continue to modulate on its own, to a point about one semi-tone above it's natural pitch.
It seems that the lower reed only wants to "start" sounding when the higher reed has been bent down far enough to reach a specific pitch where its vibration is sympathetic to a spcific upwardly modulated pitch on the lower reed. This kick-starts the lower reed, and allows you to modulate that down towards it's natural pitch while the higher reed fades out.
Wow. Way to complicated for. But it sure sounds good, eh?
---------- Rob Laferrière Russell, MB, Canada
www.woozleeffect.com
Last Edited by WoozleEffect on Feb 18, 2017 11:14 AM
Diatonics were not designed to do it. I've researched it A LOT and came to that conclusion. The physics of it are truly wacky. The article above is excellent, especially for dispelling some misconceptions. And it also states, "The physics of exactly how all this interplay between the reeds, air stream, and slots works is largely unexplored, unintuitive, and not well understood." I say the fact that they work this way borders on divine intervention. If I had a group of students that I could assign the challenge to I would certainly do it. BUT IN NO WAY EVER WOULD I TELL THEM THAT THE BLOW REEDS BEND! The coolest (and effective) thing would be to let them discover it. That would be a tricky plan to work out. They couldn't Google it and they don't know how to bend the reeds. You could do it though. Telling them first will kill it though -promise. But if you're like 99.9% of the teachers out there you will. Please consider that a pedagogical challenge.
Last Edited by Littoral on Feb 19, 2017 7:13 AM
Thanks for the info - I'm glad I'm not alone in NOT understanding what is actually happening when bending!
Last Edited by Tom585 on Feb 19, 2017 8:19 AM
There was a marathon thread a while back that might interest you if you want to delve further into the mechanics of how harmonica reeds work.
It's about reed arcing but it goes into discussions about the articles I cited above and such interesting stuff as more on Steve's Finite Element Analysis, wind tunnel experiments and so on.
I hope this doesn't complicate things; in fact I hope this makes it a little simpler.
Two forces acting upon the reed are airflow and resonance. Both are kinetic energy. Resonance can also be called "vibrational energy".
You control resonance by making an air pocket in your mouth of a particular size. You use your ears and sensory feedback to adjust the size. The size determines the frequency at which you want the reed(s) to vibrate (or not vibrate).
"Control of the size of the air pocket in your mouth" is also called "embouchure".
The really exciting part of the diatonic harmonica has been described in this thread by WozzleEffect, but I want to point out why it is exciting: Dual reed bends.
The bends - especially the 2 and 3 draw bends - involve both reeds. Since both reeds cooperate, the result is a much juicier sound than a single reed bend. As you lower the pitch of the bend, one reed takes over from the other, but both reeds work hand-in-hand.
An overblow, a valve bend or even a bent note on a chromatic may sound on-pitch, but it will not sound as full as a bent note on the diatonic.
Typically, that's the sound we are looking for when we pick up the diatonic harmonica. That's what defines the diatonic harmonica sound.
Buried in one of those papers is the observation that one (and sometimes both of the reeds) doesn't vibrate as a simple harmonica oscillator - like it would if you just twang a springy reed. That's no surprise really, as it's moving through the slot with a lot of air forces on it, not being twanged in free air.
The paper mentions the non-sinusoidal movement adds harmonics, specifically the 3rd harmonic. Which is exactly what you see and hear when you play the thing, especially hard.
We had a thread a while ago talking about acoustic volume. Winslow, amongst others, recording their dynamic range. I showed that, as the volume went up, most of it came from an increase in the 3rd harmonic. It's a characteristic sound.
There's a mechanism for your harmonica's harmonics. No need to go elsewhere, until you've ruled that obvious one out.
Last Edited by MindTheGap on Feb 22, 2017 8:44 AM
I know we've had the 'resonance' debate several times, but since you bring it up again: yes I'm sure resonance is important but it's not the only thing. It seems likely that some feature of the airflow is having an effect (speed, pressure, turbulent/laminar who knows). If resonance were the only effect, you'd have to explain why you can overblow using a straw. And you can't explain it using resonance, or tuning your 'cavities'. The key feature of flow through a straw is that it's laminar, so it seems a good idea to look at that. I'm happy to say I don't know.
Those papers are really good, but they don't attempt to go to that level. Is it important? Well imagine if we did know, then Brendan Power could find the right of sensor to sense it and add real-dual-reed-diatonic bending to that Midi harp he's been demonstrating. Imagine the power of that!!!
Last Edited by MindTheGap on Feb 22, 2017 8:51 AM
MindTheGap: You certainly can apply resonance through a straw. Why do you think otherwise?
Flow is something of which you have only limited control. You can control how much flow you apply. You have no control over whether it is laminar or turbulent - other than during the design phase.
Flow through a straw may be laminar up to a certain point. Once you exceed the threshold (Reynolds number) as you increase flow, it will become turbulent. If you want it to be laminar at higher flows, increase the diameter of the straw. Whether it becomes laminar after it leaves the straw depends on what is downstream.
I don't think there is any relevance to the fact you can bend or overbend through a straw. In fact, it's a little harder because the straw is poorly insulated and not soundproof - the greater the loss, the weaker the influence.
Conversely, it's easier to bend notes when the harp is far into your mouth because you are not wasting or losing vibrational energy.
As I remember, the Reynolds number through a pipe is proportional to the flow velocity and the diameter, so if you want to keep the number down as the flow goes up you decrease the diameter. Someone can correct me if necessary - at least that's a matter of fact.
Anyway, I don't know what regime we're in blowing through a straw, neither do you I think. But my point is that straws are often used to create laminar flows in experiments, so it's worth looking at.
My general point is that no one seems to know much about the mechanisms, so we should be wary of asserting it's definitely this or that. It's fun to conjecture but it doesn't make it real.
Bluethird has the right idea, on the throat-bending thread. He thought he was throat bending, devised an experiment to test it, and proved to himself that he wasn't.
Same with the discussion about reed failure. I'd be surprised if 'metal fatigue' wasn't involved, but there are some observations that aren't a good fit with it being the catch-all process. Or maybe it's compounded by other mechanisms.
Last Edited by MindTheGap on Feb 23, 2017 1:44 AM
...ok I may as well be hung for a sheep as a lamb...
The Helmholtz resonator. Everyone asserts that your mouth is a Helmholtz resonator and you tune it to the note. End of story. I'd be surprised if HR weren't a vital thing, but a key feature of the HR is that it has ONE resonant frequency - quite unlike other common musical things like guitar strings and bells and trumpets, which have many. That is why it was used such a lot in the early exploration of sound and speech - you can use a set of them to isolate individual frequencies. And why it's used in all kinds of engineering applications to enhance or dampen specific vibrations.
But the harmonica note is rich with many frequencies - those dual-reed bends especially, says the paper. And you mention the richness of timbre. So: multiple Helmholtz resonators? Other kinds of resonance? I don't know.
I read that a guitar body acts like an HR, but in addition it has resonances all over it's surfaces which are about the vibration of the wood, and these amplify all the notes and partials of notes on the instrument. The holes (round holes or f-holes) are not primarily to 'let the sound out' but to provide lots of different vibrating lengths.
Last Edited by MindTheGap on Feb 23, 2017 2:17 AM
So much good stuff to read and digest. Surround yourself with people smarter than you are - that's what I've done in this discussion. Always a smart move!
I suspect that Helholtz vibrations are involved. I was reading on the University of New South Wales Department of music science web site that a violin string has both a torsional and transverse mode of vibration and an experienced musician gets these in phase with each other. I wonder if something similar goes on with the Helmholz and reed vibrations in a harmonica.
Yes I expect so too. I'm thinking of 'Throat Singing' or 'Overtone Singing'. There's a few variants of it apparently, but one is where they sing a melody by picking out notes from an overtone series. So the listener hears the fundamental tone and one strong higher note. Being able to pick out one frequency like that makes me think of the that kind of resonance. But I expect it's been studied and people actually know how it's done.
It'd be like the guitarist's trick of playing a tune with the harmonics (like the Edge does on most songs, well the early ones) but while having the fundamental going at the same time. Or a brass playing playing a pedal tone and one high note at the same time - maybe you can do that STME58?
Last Edited by MindTheGap on Feb 24, 2017 1:40 AM
MindTheGAp, here are a couple things you might consider.
This figure illustrates the resonant frequency waves inside an open-ended pipe.
Also, I would suggest that a harmonica player's oral, pharyngeal (throat) cavity and respiratory tract (airways) do not form an ideal Helmhotz Resonator that would favor a specific frequency. In fact, this is where the analogy of Helholtz Resonance to complex-shaped musical instruments breaks down, and why string and other instruments can "ring" at many different frequencies.
Like a guitar or violin body, which have complicated, irregular shapes and in which a range of different frequencies can be excited, a harmonica player's resonant chamber is also irregularly shaped. Such irregular shaped chambers account for the overtone series that produces the particular timbre and character of the sound unique to each "instrument." That's why harmonica players can have different tones.
It's true that the vibrational quality of the wood used to make a violin or guitar helps influence their particular timbres but that is a higher order effect. A plastic or graphite violin or guitar still sound like a violin or guitar.
Thanks for contributing your knowledge and enthusiasm to this interesting thread.
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Last Edited by mlefree on Feb 24, 2017 6:21 AM
Who knows? I don't. And I don't have an specialist knowledge here, just general knowledge. I just observe that the harp player seems to be able to bring out lots of frequencies, and the throat-singer can pinpoint one.
In that sense, one is reminiscent of the 'guitar body', and one of a Helmholtz resonator.
Maybe harp player DO pinpoint individual frequencies, maybe it's an important part of harp technique.
Re the OP, specifically what happens when you bend, rather than resonances in general, it's often said that the player tunes their mouth to the desired note and the reeds obey. Could be. Why dual-reeds do it so well, and single-reeds don't seems to be left as an exercise for the student. As Littoral quotes for the paper, the physics is little understood. My observation is that when you start a bend, the flow resistance seems to go up a little and it feels like your doing some to the flow. It could be a side-effect or a red herring.
As a beginner on the trumpet I can tell you that controlling the flow (speed, rate and quality) is very important there! And also rather difficult.
Anyway, enough, we're not going to answer any of these questions.
Last Edited by MindTheGap on Feb 24, 2017 10:02 AM
Minds the Gap, I think we agree upon more than we disagree. But first, in speaking of Reynolds number and laminar versus turbulent flow, when you say flow velocity, I think you mean velocity whereas when I speak of flow, I mean Liters per minute (Q or flow).
If you increase the diameter of the tube and keep flow constant, velocity goes way down (resistance goes down by a power of four). I believe (please correct me if I am wrong) in your model, you are keeping velocity constant, which would mean you would need to increase flow drastically which would not be realistic here. I think that's where we are not connecting on this idea.
You are correct, there may be many other forces acting upon the reeds - we don't know.
But for me, it's a practical matter. I know flow affects the reed and I make adjustments based on empirical evidence and get reproducible results. Resonance also has a measurable, reproducible effect upon the instrument and I find myself benefiting from including that in how I work on harps - again, with empirical results.
At the end of the day, it's about what allows me to do my job better.
On certain makes and model of harps, the high notes don't bend very well in certain keys. It's not a matter of air leak or reed work. It can be addressed by making the slot of the comb shorter and/or narrower. Is this the Helmholtz resonator? Is the chamber acting as a resonator at the exact wrong frequency? I don't know really... One of those things!
What draws me in particular to the diatonic harmonica is the connection with the vocal tract. Everybody has a unique voice. Everybody has a unique way of expressing themselves - intonation, emphasis, volume, tone, attitude. In the olde days before cell phones and caller I.D., you could answer the phone and identify not only which loved-one was calling but what is their state of mind just by the first few words they say. Our ears pick up on that; it's in our genes.
What the harmonica can do - better than any other instrument (other than the singing voice), I believe, is use that. We can play the harp and infuse our own nuances to tell the story.
For me, what makes a harp sound good has a lot more to do with the person playing it. My job is to make the harmonica as cooperative as I can so that it doesn't get in the way.
Again, I was hoping to make the answer to the original question a little simpler. Oh Well!
Yes you're right. I was indeed thinking 'speed', my mistake.
I'm good with empirical evidence! The more the better. I'm just pushing back against stating simple bits of physics as the full explanation. The reason is that it's probably a lot more interesting than that, and simplifying it kills the conversation.
Most other instruments have been studied in fine detail, and it's amazing to read about the complex things going on. Much more interesting than just the basic physics principles. One of the delightful things about the harp, in an age where everything is supposed be known, is that it's still a bit (or a lot) mysterious. Making good musical instruments has, for centuries, been about skilled artisans knowing every trick, some public and some secret, and combining them in special recipes. You are carrying on that tradition - so please, don't keep it simple! :)
On the other hand, I keep hoping someone will appear on MBH who specialises in this area and unlocks some new secrets. Imagine if delving into the physics unlocked some new area: finding something so a dual-reed bend can go down to the pitch of the lower reed!
Last Edited by MindTheGap on Feb 25, 2017 11:46 PM
hi Folks, once again i don't under stand why we would care about a sound wave in a pipe as that is not what makes the reed move which makes the sound. Would we not want no how a liquid moves in a pipe too move the reed so it makes the sound we want? mX
mX, I agree with your straw issue. The illustration I posted of sound waves in an open pipe was to clarify a mistaken notion made by someone who asserted that waves don't resonate in a straw.
I find any comparison of water flowing through a pipe to a harmonica even more remotely relevant, however. Or maybe I don't understand your question. 8^)
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Oh that's why you posted it. Ok, yes I do understand that you can have resonance in a straw. The question is whether that's what is causing the overblow in this case. In Ben Hewlett's demo of this effect (link below) he gets OB in holes 4, 5 and 6 with the same straw. It's possible that by chance he's chosen a straw of the correct length that has resonances at all the right frequencies. Worth a think though isn't it? Just in case it isn't that?
What I'm saying is it's best to keep an open mind until you know for certain. Certainly useful to have a working theory, but if a bit of evidence comes along that doesn't fit very well, it's normal practice to question it.
I think we're getting nowhere again with these discussions - you'll have to believe what you like. Let's enjoy the magic. I bet there's some interesting resonances going on here, probably no drinking straws involved but I expect she'd play a mean harp...
It's not a matter of belief. As they say, science doesn't care about beliefs.
The answer to the question as to why you can overblow through a straw is found in the subject of Helmholtz Coupling. Google reveals many references to Helmholtz Coupling. Here is one of the more directly relevant.
As the abstract says, "The coupling is described by the mutual impedance between the neck openings, and an additive reflection impedance modification to the radiation impedance, which models the effect of reflections from the outer ‘‘shell’’ of the other resonator."
To understand what that means requires working knowledge of some pretty high falutin' math. It's been a while since my days of muscling heavy mathematical equations in engineering school, so I'm a tad rusty. Suffice it to say that one Helmholtz Resonator can become acoustically coupled with another under the right conditions of chamber volumes and neck sizes to "change the resulting sound." As the article states, "In some musical instruments, the coupling may lead to undesirable detuning and possible beat effects. These phenomena lead to increased workload for instrument builders and tuners since an interactive building approach is then needed to correct for the coupling, which cannot be estimated beforehand, but is obvious when the instrument has been assembled. As an example, the possible importance of the coupling in flue organs is illustrated by Fig. 1, which is a picture of the interior of a large pipe organ. It should be mentioned here that the ear is particularly sensitive to small changes in frequency, which means that even effects of very weak coupling can be audible."
So, what's going on with the straw experiment is that the Helmholtz Resonator formed by the straw is being acoustically coupled with the reed chamber in a way that chokes the draw reed and causes the blow reed to sound. Evidently the harmonics in the straw are such that this works on several holes of a given harmonica. It has nothing to do with the straw directing the flow of air.
BTW, this is the same principle behind Brendan Power's new "Powerplugs." They adjust the size of chromatic comb chambers to "overcome the effects of Helmholtz Resonance Coupling" that make higher notes difficult to sound in chromatic harmonicas. As Brendan puts it, the resonant frequency of the stock reed chamber "fights" the frequency of the vibrating reed.
So you reckon that the straw is one Helmholtz Resonator, and the chamber is another? But a HR has a specific frequency that depends on it's dimensions. So how does the same straw work on different holes?
Earlier on, you showed a diagram of standing wave resonance in a pipe (straw). I took that to mean you thought it was that kind of resonance that was going on. Which do you think it is? (I don't know, could be either or none).
Brendan Power's article talks about the problem of the high reeds not sounding because the reed's frequency and the resonance of the chamber aren't similar. When he changes the size of the chamber, it can work better so that seems consistent. That's his 'resonance coupling'. That paper you mention, though, is about the coupling of two resonant chambers (e.g. in a pipe organ). Is it relevant? I can't do the maths either, but more to the point I don't know if the situations are even similar.
Brendan describes an experiment by Rick Epping where he makes a little 'pan pipe' from a harp comb, and blows across the top to find the natural frequency of each chamber. So some data can be had. No hard maths or theories about how the sound is generated or what kind of resonance is going on - he just measured it.
Last Edited by MindTheGap on Feb 27, 2017 8:16 AM
...I don't know I'm lost now. It's just all this insistence on Helmholtz Resonance. I can't get over the thing that traditional HRs are like a bottle - i.e. with a relatively big mass of air and a narrow neck, and the harp's chamber isn't like that. All the instruments I read about that do use HR like Ocarinas and Jembes are 'bottle-like' too. I didn't think pan pipes were though?
I can see that a mouth/lips can be 'bottle-like' too. But earlier on you said "I would suggest that a harmonica player's oral, pharyngeal (throat) cavity and respiratory tract (airways) do not form an ideal Helmhotz Resonator that would favor a specific frequency"
Then I went and starting reading a paper about end-blown flutes. And it's fantastically complicated. Far too complex to apply simple principles to.
I'm out.
Last Edited by MindTheGap on Feb 27, 2017 8:37 AM
Hi just me again, The thing is air or water moving in a pipe is just liquid moving in the pipe so we can use the same math for either. So the thing to note here is that pressure decreases when velocity increases so to me this is what is being manipulated with the shape of the chamber by changing embouchure in you or the straw. MX
Like Michelle, it has been a while since I have done the serious math, but you might be able to find a geometry for a water flow harmonica that has similitude with a normal harmonica. This would probably only work if a harmonica is basically incompressible flow, which is not the case if Helmholtz resonance is a significant factor. If you could find a geometry that worked and had similitude, the water harmonica would allow you to study things in a way you could not on a standard harmonica.
MindTheGap, I'm saying that this is a very complicated system we're talking about with Helmoltz Resonance and Coupling occurring at multiple levels.
The reed chamber is one Helmholtz Resonator with the open part of the chamber the volume and the restriction of air flow due to the gap between reed and reed slot being the "neck." As such each reed chamber has a time-varying resonant frequency because the size of the gap (neck) changes rhythmically as the reed opens and closes. Thus there is a range of natural resonant frequencies that can be excited as the characteristics of the Helmholtz Resonance change within the chamber over time.
Then there's the straw which is also capable of resonating at a range of frequencies defined by its harmonic series. To further complicate the situation, the straw and the player form a "system" in which the player is able to tune his oral cavity and upper respiratory tract "chamber" to different frequencies (and the straw is the "neck"). [This is what I meant when I said that the player's airways don't "ring" at a specific set frequency as in a simple Helmholtz Resonator. We see this all the time when we bend notes. I didn't mean to imply that the player's airways don't constitute a Helmholtz Resonator.]
So for the sake of this discussion I posit that there is Helmoltz Coupling going on inside the harmonica. If we think of the player and the straw "system" as one Helmholtz Resonator and the reed chamber as another, there is Helmholtz Coupling between the straw/player and the reed chamber. Each contributes to the change in frequency of the resonance in the reed chamber due to Helmholtz Coupling that in effect results in the same action that excites normal overblows. The draw reed chokes and the blow reed vibrates at a higher harmonic frequency that it usually does.
You seem hung up trying extrapolating what you know about a simple, classic rigid cylindrical chamber with a neck on it to all forms of Helmholtz Resonance. You seem unable to accept that in a complex-shaped chamber like the body of a guitar or a violin, a player's airways can resonate at multiple, even time-varying frequencies. [Further, it is the harmonic overtones that ring in a guitar that gives it it's unique timbre compared to other string instruments, just as singers have their own sound.]
Simple Helmholtz Resonance obviously doesn't explain what is happening in such a complex system. Classic Helmoltz Resonator experiments offer little bases for inferring what is happening in such a vastly more complicated situation. So I agree with you to the extent that further discussion will be unproductive if we can't get past that limitation in our thinking.
I've offered a number of increasingly complex explanations complete with references. You've offered a lot of critiques and random facts. If you are so convinced that Helmoltz Resonance and Coupling don't offer plausible explanations, I'd like to know that you do think is going on. Until I see you develop a similar coherent explanation that cites references and builds a case beyond what you know about simple Helmholtz Resonators I feel no further obligation to continue this discussion.
Steve and mx, it is true that air and water are both fluids and subject to the same science and equations of fluid dynamics. But the physical characteristics of air and water such as density, viscosity, and compressibility among others as represented in such equations are so vastly different as to render any water-based flow experiments in some sort of a reed chamber model moot, IMO.
At least that's the way I see it.
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Last Edited by mlefree on Feb 28, 2017 6:03 AM
Hi folks, what confuses me the player is able to tune his oral cavity and upper respiratory tract "chamber" is this not before the note is made. so there is no resonant frequency. chamber like the body of a guitar or a violin is this not after the note is made, so now we have a resonant frequency. MX
harpwrench I'm sure you're right about how we pre-shape the notes. What you're describing even works just one or two holes apart. If you sound a blow note in hole 4, and then try to change absolutely nothing about your mouth and play that note exactly the same on hole 6... it can either choke out out sound awful. The closer the holes are together (and the closer the notes are together) the easier it is to play those two notes without any change in the way we sound the note with our mouths.
If you play a D in 4 draw, get that note stuck in your head, and try to play that same D on 5 draw... what happens? Probably a pretty crappy sounding F...
I've read and posted that Robert Johnston on "Pitch Control In Harmonica Playing" article a number of times. It's based on some heavy duty math but Johnston hid most of it pretty well. The result is readable by patient if non-technical readers.
I've gone to the trouble of bypassing the math and sifting out the gist of this important article by cutting and pasting sections of the germane text.
For example, here he states in plain English what goes on inside a player's oral cavity and airways during bending.
Further down in the article he goes into great detail about opening and closing reeds and how they interact during bending, including insights about overblows.
Some one asked, so here he describes reed dampening.
And to underscore the impact of Helmholtz Resonance,
I hope this helps some to understand this landmark article, clears up some points and answers some questions.
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Last Edited by mlefree on Mar 03, 2017 2:09 PM
I can't help returning to this, only to understand why people are so certain about what they think and why there is so much disagreement.
What harpwrench describes is the resonance from standing waves. A perfectly nice resonance and responsible for lots of music including singing, so I always thought. Helmholtz Resonance is a different thing and has different characteristics, and present in some instruments too. I think it's likely that either or both could be used to play the harp, either in an experiment or in real play.
It occurred to me, reading back, to wonder if maybe people aren't quite clear that they are different and in what ways. Clearly STME58 does, from his response to mx (about a water experiment). When Brendan Power writes 'Helmholtz Resonance is causing problems with high reeds' in his article, does he really mean 'Some Resonance is causing a problem'? He doesn't say why it's specifically HR, but then he may write in and say he's done some experiments and shown it has HR characteristics and his calculation of the chamber HR resonance is consistent with the measured frequency, and inconsistent with standing wave resonance - in which case, it probably is that.
Anyway maybe not, but it would explain a lot of the strange disagreement in this and other threads. And we could all go dancing off, and resonating, into the sunset.
Last Edited by MindTheGap on Mar 04, 2017 11:11 AM
MindTheGap, I don't know about you but I am so certain about what I think for several reasons.
1) I make no claim to being a James Antaki, Ph.D. but I do have training at the graduate level in the physics of acoustics including a full semester studying the 3-dimensional acoustic wave equation; 2) I have researched and read all the available scientific literature on the subject of harmonica physics, much of which I've cited here, including my most recent parsing of the Johnston paper; and 3) my knowledge of the fact that the wavelengths of the harmonica sound waves are orders of magnitude longer than the dimension of any reed chamber, such that sound waves aren't reflected within the chambers or back from the player, and thus the reeds only serve to chop air flow, and that is what causes the various physical phenomena we seek to understand. It's a matter of resonance and resonance coupling and not waves bouncing around.
Others have presented conjectures without citing any prior work or science to justify them. Curiously, you disbelieve the very Johnston article you've cited, yet freely admit you don't understand ("Good luck with it."). Even when I make direct quotes that explain the gist of the article while removing the math, you cling to your concern about disagreements on the subject. Just because you don't understand something doesn't make it false.
I'm beginning to wonder how you might feel about climate change.
Maybe we should just leave it at that.
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Michelle, I do think it's likely that Helmholtz resonance is involved. And I'm sure you know the difference, I was pointing out that harpwrench described standing-wave resonance and thought it was that. mx suggested using a water-based analog which I don't think would be relevant for looking at HR, as STME58 said.
Unfortunately I can't see your extract images (I get a message about https protocols) but I did read the paper looking for your model of two coupled Helmholtz Resonators with a time-varying resonance based on the reed opening being the 'neck' of the bottle, but I couldn't find it. As you say, I don't get the maths so it may be in there but I can't see it, and I'd be grateful if you can point it out. Just give me a paragraph or a bit of text as a bookmark - I still may not understand it though!
What is in the paper is that he uses an 'artificial mouth' based on some other work on mouth resonance in flute playing http://gjk2.com/stuff/mouth.pdf and that is indeed a Helmholtz Resonator which they modelled on the resonance of around 1000Hz found in a real mouth. In that case they were looking at small variations in pitch in flute playing rather than the big primary effects we are talking about with the harp. They do talk about resonance coupling and they see a split into two frequencies but it's between their artificial mouth and flute, and the flute is using standing-wave resonance (or so I think, they talk about the 2nd mode).
If it's all about HR in the mouth, and (as you say) there's no waves being reflected around in the vocal tract then that's interesting. It's often said by the musicians that they get the best tone with the 'airways wide open down the diaphragm', with the image that your vocal tract and other bits were resonating away. I guess the analogy is made with singing. I thought I saw a video from Steve Baker about that specifically, I'll have to go and have another look.
Another interesting feature in that 'mouth' paper is that the Q value of their 'mouth' varied a lot with the airflow - meaning I think that you could get a much stronger resonance effect at lower flow rates (I think I read that right). Now that's definitely worth a look!! BBQ is often saying how the harp should be played very gently - what if it's something around that?
Last Edited by MindTheGap on Mar 04, 2017 2:18 PM
Michelle, I just looked up the notes on Chromonica 64/280 and it goes down to C3 = 130Hz, can a mouth HR go that low? I'm asking because you are able to do the calc.
In the paper they say they found the "mouth's" volume as 3.6cc at 1000Hz - that sounds quite small to me actually, for a mouth. But I guess you can make the cavity as tiny as you like. With everything else equal, what would the volume be at 130Hz?
Last Edited by MindTheGap on Mar 04, 2017 2:00 PM
The other thing I've always wondered about is: if I blow into the low notes of a harp from a little distance, the notes sound but it's a tinny little sound. If I play the same notes with the harp in my mouth, but make no attempt to 'tune' anything, just blow gently, I get a much louder rounder sound.
Then I play a chord of holes 1-4, and ALL the notes of the chord are amplified. There's a whole octave between them, but the same embouchure. What's going on there? I always thought that was resonance in the head and vocal tract, similar to singing. Then I know that if I drop my jaw on the low notes I get a richer sound again: I rationalised this as the sound was probably a mix of mouth-cavity resonance and other resonances available. Is that wrong?
Last Edited by MindTheGap on Mar 04, 2017 2:17 PM
Re Brendan Power's problem with high reeds, that Chromonica 64 goes up to D7 = 2349Hz In a stopped pipe, the first resonance is at 1/4 wavelength. I wonder what 1/4 of that wavelength is, and if it's similar to the path length in his harps? If it were, then it would be hard to totally rule out that resonance. He may have done that analysis though, in which case job done!
All interesting stuff to ponder thought, isn't it.
Last Edited by MindTheGap on Mar 04, 2017 3:26 PM
A while back I made a spreadsheet of Helmholz cavity volumes that would resonate with various neck lengths. You can find it here . I don't think that assuming the comb slot acts like the neck of a Helmholtz resonator is a reasonable assumption, but I was curious what the math would show. The spreadsheet calculates what volumn would resonate at various frequencies with a 6mm x6mm x various length necks.
Can't help thinking What would LW,BW.SBW,HW,etc etc would of thought about this discussion? Personally even though i don't pretend to understand any of it,i do find it interesting. So thanks guys.
STME58, unfortunately I don't have dropbox account to see that - but what did it show? Did you have the mouth being the 'bottle' and the reed chamber being the 'neck'? That's were I'd start - at least there are some actual dimensions to work with.
The Rick Epping experiment described by Brendan is a bit different - making a pan-pipe out of a comb and blowing across the top. That 2nd paper I mentioned http://gjk2.com/stuff/mouth.pdf about the side blown flute they're looking at the mouth-cavity resonance changing the pitch a bit, but not much.
My first guess would have been that you'd get a pitch roughly corresponding to the 1/4-wave length stopped pipe. But then again, the lengths are so small that it might be blurred by end effects. If we had the results of that it would be interesting to look at.
I wouldn't know how to model the HR resonance of a reed chamber, without the mouth, but the HR resonance frequency varies as 1/sqrt(volume) whereas the stopped-pipe frequency varies as 1/length. So you'd hope it would be possible to compare all ten holes and see which it is. Nothing's ever that simple though!
Last Edited by MindTheGap on Mar 05, 2017 12:50 AM
indigo - glad you're finding it interesting! Actually I think it's all a load of conjecture. We can point to all the papers we like, but without some actual modelling vs experimental results, it's just chat. But, hey, it's a forum - what else is that for!? What's interesting to me is that it has teased out a number of apparently contradictory views for what might be going on, and what's important and what's not.
I reckon that various types of resonance are involved, and I'm basing that on partly on what people have said about producing good tone (you know, from the diaphragm), partly from simple observation (stick a harp in your mouth and the sound is amplified, without special effort) and from what I've read about the singing voice is produced. But I don't know that. If someone shows by model+experiment that Helmholtz is the only game in town then I'll take that, and have learned something.
Also I think it's worth not ruling out that the air flow may have an effect. For instance in the 'mouth' paper they seem to say that it does, at least for a flute.
Personally I like the idea that blowing more gently gives more resonance! I hope I've read that right and it's not the other way round.
Last Edited by MindTheGap on Mar 05, 2017 5:42 AM
MindTheGap, I did not think you needed a Dropbox account to access things in my public folder. My spreadsheet numbers came from starting with reed chamber volume for a 6mm x 6mm by various length chamber and finding the resonant cavity volume required for that "neck" size to resonate at various frequencies associated with notes in the 12 tone equal tempered scale. Anyone who thinks about this a bit, will realize that the geometry of the reed chamber, with openings on the side rather than the ends and two reeds obstructing the opening in a time dependent way, is nothing like the neck of a bottle, but as you said, it is a starting point.
One I ~never~ said or implied that it's all Helmholtz Resonance -- in the mouth. I don't know where you got that idea. In fact, both my previous posts and the image captures I just posted from the Johnston article that you apparently can't see state quite the opposite. Just for your benefit I'll type the contents of the first capture out.
"E: The technique that is used to achieve these changes, while complex, is essentially as follows. For medium to high pitched notes the size of the oral cavity, controlled by the position of the tongue, seems to be the crucial factor. For medium pitch draw bends , the tongue is pushed down and back to flatten the pitch. For the high blow bends, the tongue is pushed forward and as mentioned above the pitch drops more or less abruptly. In both cases, the higher notes are played with the tongue further forward in the mouth. For very low pitched notes the movement of the tongue is less pronounced and it is noticed that the Adam's Apple drops on bending to lower pitch, and this is an indication that the larynx is being lowered [5]. These changes in tongue position are similar to those found in woodwind playing."
This is fully concordant with my previous statements about the player's airways contributing to their resonant chamber. You may wish to go back and read them. And yes, the reason players open wide to achieve improved tone is, guess what? They make a bigger resonant chamber that allows lower frequencies to resonate and higher order harmonics to sound. Further,the reason that your tone is tinny when you blow your harmonica from a distance is that, surprise, there is no resonant chamber. I just don't understand why you find it so difficult to believe that Helmholtz Resonance can account for these observations. It seems obvious to me and, I might mention, the scientists who've written about this subject.
For completeness, what I meant by sound waves bouncing around inside the mouth is that they are of such a long wavelength that it is erroneous to think that sound is reflecting off of the surfaces like a light in a headlight reflector or sound in a soundproof booth. It's a matter of R-E-S-O-N-A-N-C-E not reflection.
You appear unable to take your thinking further than your slippery grasp on simple Helmholtz Resonators. You vigorously deny anything that deviates from that rudimentary framework. You seem content to sit back and proffer randomly selected pot shots even though you don't read your own reference article. I could be off base but to me you are coming off as the kind of person who enjoys criticizing someone else's statements because they are unable to offer any of their own constructive ideas. Please prove me wrong.
At this point I feel no further obligation to try to help you understand the extremely complicated mathematics and physics required to explain this stuff when you seem so unwilling to learn. I've given it my best shot.
Michelle
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Steve, I don't think the reed chamber is the neck. I think the "neck" is the space formed between the reed and its slot. In my way of thinking the reed camber would be the resonant chamber.
Michelle
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