Just to toss in some additional information about Helmholtz Resonance and its role in playing harmonicas, I mention that Douglas Tate wrote in is book, "Playing The Harmonica Well" about his use of "hand resonance" to allow him to be heard over an orchestra without using a microphone. Robert Bonfilgio uses this to good effect as well.
Basically, you adjust the size of your partially open hand cup based on the frequency of the tone you are playing. Pat Missin wrote about it too, complete with examples.
Michelle, I can see your point, but like the drunk who dropped his car keys, I'm looking where it is easier to see, not where the keys are likely to be. Time varying openings complicate the calculations :-)
Last Edited by STME58 on Mar 05, 2017 12:16 PM
Michelle, I hadn't done that because I was thinking of the opening as a wedge shape that changes as the reed swings. I modeled it as a slot around the reed of constant thickness (.005 in) and length of the thickness of the reed. This is not quite right as the reed actually sits above the reed plate. It would be more accurate for an idioglottal reed. I varied the comb slot length (10 to 20mm), the reed length (7 to 19mm), and the gap between the reed and the reed plate(.001 and .002 in). Sorry about the mixed units, I am much more used to dealing with small thicknesses in inches. All lengths were converted to meters for the calculations. Surprisingly, the frequency stayed in a range of about 150 to 250Hz.
I found out why the spreadsheet was not accessible to others in my previous post, I had not used the public link. This link should work.
Last Edited by STME58 on Mar 05, 2017 7:58 PM
Michelle - you say of me "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"
Earlier on you said "I'm beginning to wonder how you might feel about climate change." That's a belittling comment whose implication is clear to anyone, although I expect you thought you'd kept within forum rules by avoiding a direct insult.
That's all unfair and unbelievably rude. I have suggested a reasonable alternative which is that when playing the harp there are probably a mix of resonances involved from various bits of the body, throat and head, just like in singing. It seems like a reasonable explanation of why different players have different 'voices' on the harp, just as they have different speaking voices and singing voices. The papers we've looked out don't discuss timbre, other than in the flute case where they say their 'artificial mouth' doesn't sound that great. It seems likely to me, from reading those papers, that Helmholtz Resonance in the mouth cavity (and yes that can include the throat) is strongly involved particularly in bending a note, and that other resonances are involved in adding timbre.
What you dismiss rudely as 'pot shots' are actually just naming some commonly experienced effects people get playing the harp. Any decent theory should be tested by using it to explain these things. They are of interest.
Just for instance, a key feature of Helmholtz Resonance is it amplifies strongly around one frequency. But when you play a chord, with a harp in your mouth, a wide range of frequencies are amplified, and very clearly. I could imagine explanations that involve just HR, and ones that involve a mix.
Very clearly, a harp can sound without any Helmholtz Resonator attached e.g. by holding it out of a car window. Before you shoot me down in flames again, yes I forgot to say the car has to be moving :) These are interesting features, worthy of discussion beyond the simple "I'm right, your wrong".
As for saying "It's a matter of R-E-S-O-N-A-N-C-E not reflection." Well, while it's true that Helmholtz Resonance isn't caused by reflection, other kinds of resonance are. And the more common ones in music are caused by reflection: guitar strings, trumpets, organ pipes, oboes. Since you mention Pat Missin, he describes one kind of hand resonance that does look like Helmholtz (cupping round the harp with a little hole) and another that looks like reflection i.e. a standing wave (a shimmering effect on high notes by holding the hand some distance away from the harp).
Last Edited by MindTheGap on Mar 06, 2017 2:20 AM
...anyway that's my case. I do understand we disagree, In an nutshell, I currently think harp playing could involve a number of resonances, and you know it involves only Helmholtz Resonance. Have I got that right?
If so, my ideal is that we put that to one side and continue to discuss some of the interesting bits of physics, without the insults. When a paper comes along that proves all the features of harp playing are actually caused by HR, I'll very gladly accept it.
My dad was a physics teacher. My grandfather was a GE Engineer. My uncle was a mathematics professor and my aunt got a perfect score on her SATs. Whatever genes I inherited didn't prepare me for the heady content of this thread!
Remember people, this is complicated stuff. Theories are meant to be debated, but that doesn't mean we can't stay civil.
Hopefully back on track now. My aim with this is to see if we can use some principles and observations to discuss the harp, without resorting to difficult maths.
The harp is a relatively young instrument. Take the example of the trumpet, which of course was in use a long time before the maths to describe it, but it's been studied a lot since. How it works is fascinating, and the ideas are open to anyone without a maths background, but particularly with a musical background because it's couched in terms of the notes that you'll know. Start the principle of the standing wave in a tube or a string, and see how it's modified to give a practical working trumpet. It's not just about the valves, it explains things like the timbre and how it changes across the range of pitch and volume.
Can the all the features of harp-playing be described in this style? Not by me certainly. I was hoping someone else had done it.
What's the Number 1 thing that harp players value, what do they strive for and remark on in others? Tone. If someone can unlock that secret, that would be something. Some say it's a given thing, others say it can be developed. Some say different reed materials give a different tone, for some it's different comb materials.
Last Edited by MindTheGap on Mar 07, 2017 1:15 AM
MTG, good tone isn't secret. Pat Missin explains it: overtones.
"Well, by carefully altering the shape of your mouth as you play, it is possible to enhance certain of these overtones and thus alter the tonal characteristics of a given note, using a similar technique to that used by guimbarde players and throat singers (overtone singers)."
And from Wikipedia, "The harmonics (fundamental and overtones) of a sound wave made by the human voice can be selectively amplified by changing the shape of the resonant cavities of the mouth, larynx and pharynx.[1] This resonant tuning allows singers to create apparently more than one pitch at the same time (the fundamental and a selected overtone), while actually generating only a single fundamental frequency with their vocal folds."
So, yes, it's harmonic resonance, closely related but not equal to simple Helmholtz Resonance. A chamber, if not perfectly cylindrical, and not having a well-defined "neck" still cause sound waves to resonate.They just do so without a singular dominant frequency. And in fact, as the Missin article states, a player can manipulate the overtones in his resonant chamber. He goes on to say, "The best way to do this is to spend a lot of time playing long single notes and experimenting with your mouth shape whilst paying careful attention to the tone you are producing. Try shaping your mouth and tongue as you would when pronouncing different vowel sounds and listen closely to the effect it has on your harmonica - the development of this skill is not so much learning to do it, but more a case of learning to hear what you are doing."
We are seeing that the answers to all these questions keep coming back to resonance and resonant chambers.
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Last Edited by mlefree on Mar 09, 2017 3:17 AM
"...The harmonics (fundamental and overtones) of a sound wave made by the human voice can be selectively amplified by changing the shape of the resonant cavities of the mouth, larynx and pharynx.[1] This resonant tuning allows singers to create apparently more than one pitch at the same time (the fundamental and a selected overtone), while actually generating only a single fundamental frequency with their vocal folds".
Excellent, I agree!
(With the harp there's also the hands, and many say the metal used in the reeds and the comb material are important too.)
Where I'd like to get some clarity is the nature of the resonances. All the articles I've read say pretty clearly that the vocal tract is a tube with standing wave resonance. For example, here's an extract from http://hendrix2.uoregon.edu/~dlivelyb/phys152/L10.html#HV
This describes the production of sound signals within the vocal folds and larynx. The larynx, pharynx, oral and nasal cavities can be though of as a resonance chamber. The resonant frequencies of this chamber are controlled by altering the shape of these cavities and, thus, serve to filter the sounds produced.
So far so good, then...
Thinking about the boundary conditions of this chamber, we note that the bottom of the larynx, just above the vocal folds is a pressure antinode. The other end, at the opening of the mouth, is a pressure node like the end of an open tube. We recall from earlier lectures that the overtone series for this type of chamber are odd harmonics. The overtone content (amplitudes of the odd harmonic overtones) can be adjusted by shaping the resonant cavities, forming vocal formants. This is accomplished mostly by manipulating the tongue, lips and the soft palate.
Vocal formants are frequency regions where harmonics have large amplitudes. The speaker or singer controls the frequency of the source sound by tensioning the vocal flaps, and controls amplitude by varying the average air pressure available just below the vocal folds. The vocal "tube" is about 17 to 18 cm long for the average individual, with resonant frequencies of about 500, 1500, 2500, 3500 Hz and so on. The principal vocal formants are at these frequencies, but can be manipulated simply by manipulating the tube diameter at the position of nodes and antinodes for various overtones.
Last Edited by MindTheGap on Mar 09, 2017 6:05 AM
So that article is about the voice, using standing-wave-type resonance to shape the harmonics. But it's worth considering if it applies to harp playing too. With standing-wave resonance frequencies as described, it's worth thinking whether they might contribute to harp playing. BTW I'm not citing this article as the source of all wisdom, but it's similar to articles I've read about the voice.
The papers we discussed earlier used an 'artificial mouth' which used HR to single out a frequencies to make to make the reeds sound and bend etc. Is it then true that that is the way real mouth operates? I don't think they actually state that in the article - maybe any type of resonance will do. Was the choice of a Helmholtz Resonator specifically so they could single out individual frequencies? That's a common use for them in experiments.
What I can't find anything about is your idea of a kind of Helmholtz Resonator where "A chamber, if not perfectly cylindrical, and not having a well-defined "neck" still cause sound waves to resonate. They just do so without a singular dominant frequency"
Can you provide anything? To be clear this is not a pot shot or personal criticism, I want to learn about something new (to me). The resonance coupling described in the flute paper involved two resonance chambers - that resulted in a split frequency.
Any references gratefully received - genuinely!
Last Edited by MindTheGap on Mar 09, 2017 5:57 AM
MindTheGap, Have you looked at the University of New South Wales Department of Physics and Music Acoustics website? There is nothing there on the harmonica, but I found the research on the Sax interesting. Part of the research indicated that the sax's conical shape made it more responsive to vocal tract changes than the similar, but cylindrical clarinet. I have found from personal experience that a trumpet is much more responsive to vocal shaping of tone than a trombone, but neither is as responsive as a harmonica.
Another point alluded to in this thread, that is not physics, but I find it fascinating, is biofeedback. Practicing long tones, on any instrument, is biofeedback. The tone is the feedback mechanism. We make changes, and when we hear a tone we like, we learn to replicate that condition to get the good tone. We really have no idea what is really going on inside our bodies that causes the good tone, we just hear it and learn to do what causes it. Many people confuse what they are thinking about when they get the good tone with what the muscles are actually doing. This, and the fact that there are likely many different combinations of factors that can produce a good tone, are probably the source of a lot of the confusion around tone production.
PS: I enjoyed your links to trumpet physics. I may have to make myself a PVC bugle!
Last Edited by STME58 on Mar 09, 2017 12:17 PM
STME58, re your observation on trumpet: on this page on brass, right at the bottom, they look at whether trumpet players tune their vocal tract to play the very high notes, given that they use tongue placement and mouth shape to change register and intonation: apparently 'no'!
What I take from this for the harp, is that it's always worth considering that different mechanisms might be used at different places in the range, or for different techniques. Just because we think we've found an explanation for one thing, doesn't mean it's applicable everywhere. I guess that the nub of my concern about applying specifically Helmholtz Resonance to explain every harp sound, it just seems unlikely to be down only to one thing.
That's a very good point you make about biofeedback. And what you think you're doing vs what you're actually doing. I'm happy with teachers using metaphor to get you to play better, but when they start saying it's actually what's going on physically, that's going too far.
Last Edited by MindTheGap on Mar 10, 2017 12:00 AM
I took up the trumpet recently, good grief I didn't think it would be as hard as that - particularly how long it takes to play the higher notes. Even the not very high notes.
Here's the article on Helmholtz Resonance, and it describes guitars and violins with a bit of practical detail. I'm still in search of the resonator that Michelle describes - I just cannot find anything though.
http://newt.phys.unsw.edu.au/jw/Helmholtz.html
Last Edited by MindTheGap on Mar 09, 2017 11:52 PM
I have to say that that UNSW site does go into some detail about voice production, resonances and filters in the vocal tract. And while there is a lot of detail and some maths, the basic principle they discuss is resonance based on reflection.
http://newt.phys.unsw.edu.au/jw/voice.html#origin
This squares with everything I've read in the past. So I think I can be forgiven for assuming that this applies in harp playing too. And for being surprised that so many harp players say that Helmholtz Resonance is the important (or only) thing. Doesn't mean it isn't - that would be even more interesting if singing were to use one kind of mechanism and harp playing a different one.
So I'll ask again - please someone, anyone, post a reference to the vocal tract working purely as a special kind of Helmholtz Resonator, either in singing or preferably in harp playing. I read the statement of fact so many times there must be a source surely? It can't just be something that a harp player/builder said, however venerable. Nor the Wikipedia article on HR - I know it exists.
I'll keep looking myself.
Last Edited by MindTheGap on Mar 10, 2017 3:08 AM
MTG, with these last few post of yours I've gotten over my feeling of having been trolled. I apologize for falsely accusing you.
Now, to avoid the both of us having to sift through some mighty dry and technically involved scientific literature, I think I'll use guitar resonance as auditory and visual examples.
Here's a video where a luthier uses Helmholtz resonance to design the size of the sound hole in one of his unique looking instruments.
You can hear that, by changing the size of the air hole, how he can vary the frequency of the air vibration inside the sound box.
You've no doubt seen Chladni patterns on drum heads where some salt or sand is used to show the nodes and antinodes of the surfaces of the vibrating drum head.
I'll call your attention to the varying latitudinal "diameter" of a guitar top, from the wide part at the tail through the typical hourglass narrowing and on to where it widens back out but to a lesser degree towards the neck. One can think of a guitar top as several different connected drum heads. The wider area towards the tail stock vibrates at lower frequencies than the narrower area near the neck.
Here's a nice interferometry image showing the same thing in greater detail.
You can see how, as the exciting frequency of the vibrating air at the sound hole rises, higher order (more complex) vibrational patterns (modes) are excited in the guitar top. Luthiers go to great lengths to design structural ribs that are glued to the inside of the top to try to ensure an even magnitude of resonance across the range of frequencies the instrument can produce. In fact, poorly designed guitars have non-uniform levels of resonance that cause undesirable loudness at certain tones.
This guitar forum reply is to a player complaining that one of his strings sounds much louder than the others:
"Open strings always sound different to fretted notes - more resonant and with more sustain. Players of string instruments learn to avoid open strings for that reason, and sometimes to take advantage of the different tone of an open string.
Other than that, it does seem that you've identified a resonant frequency in the body of your guitar. That is probably a symptom of a cheap guitar - better guitars will have been crafted to have a pleasing set of resonances, with no glaring anomalies.
A luthier may be able to fix this by shaving wood away, or by building up the soundboard. Depending on the value of your guitar, the cost of the luthier's time may not be warranted.
As your link, and Tim, have suggested, you might be able to achieve the same thing by sticking things to the inside of the soundboard; experimenting with different positions. The intention is just to damp the vibration of the part of the soundboard that resonates at that frequency.
Tuning up/down a half tone, while playing the same positions, would let you avoid the problematic frequency a lot of the time. However, it would prevent you from playing along to recorded music, and from playing with other musicians with normally tuned instruments. It may also affect your ability to sing along to your own playing, depending on your range -- although one semitone shouldn't make too much difference.
Of course, tuning down a half tone, then playing a fret higher to compensate, will not help at all - you will still be playing the problem frequency, and your guitar body will continue to resonate.
If you're not playing along to recordings or other players; or if you can get the other instrumentalists to tune to match you, you could detune by a fraction of a semitone. Even a very small change may be enough to take you away from the resonant frequency."
Now, one might ask what all this reference to vibrational modes of guitar tops has to do with my assertion that "A chamber, if not perfectly cylindrical, and not having a well-defined 'neck' still cause sound waves to resonate. They just do so without a singular dominant frequency." What happens in actually playing a guitar is that, just as an external sound generator was use to induce vibrations in the guitar top, so does the sound due to the strings vibrating at the sound hole. And both the harmonic series at which the strings vibrate as well as the higher order vibrational modes of the guitar body add up to inducing resonances that create the unique timbre of the instrument. All guitars sound like guitars in general, but there are significant differences between various maker's instruments and even differences between the tones of individual players.
Obviously, the tissues of human airways don't have the same kind of vibration that rigid guitar bodies do. But you can feel your own mouth and throat vibrate when you sing or play harmonicas and if you're an accomplished player who knows how to open up throat and drop your Adam's apple you can feel the vibrations all the way to your diaphragm.
I hope you get my meaning.
Michelle
---------- SilverWing Leather - Custom leather creations for musicians and other eccentrics.
Last Edited by mlefree on Mar 10, 2017 3:51 AM
Michelle - Great! All good. Apology accepted. There's absolutely no trolling here, and no malice of intent. But I want to clear that I am disagreeing with you, in some particular things - well, one particular thing, and questioning some of the received wisdom. I expected to get some flak for that of course, maybe not quite as much! :)
That's an excellent piece about the guitar. So from what I understand it has:
1. Helmholtz Resonance caused by the bulk of air in the body and the sound hole. It's at the low end of the spectrum, and can be altered by the size/shape of the body and the hole. It has ONE resonant frequency, although that can be spread out a bit by damping. That UNSW site says this resonance is, "...often near or a little below the frequency of the second lowest string, around D on a violin or G-A on a guitar"
2. Standing-wave resonance in the wood of the guitar body, caused by reflections in the normal way. That's what is visible in those pictures. There are many resonant frequencies caused by the different path lengths in the wood and the vibration modes. As you say, "You can see how, as the exciting frequency of the vibrating air at the sound hole rises, higher order (more complex) vibrational patterns (modes) are excited in the guitar top". It's vibrations in the wood, not the bulk of air as in HR.
Together these two effects amplify the different harmonics of the strings and give the timbre. And we DO agree on that! The analogy with the harp (and it is just an analogy) is that we may have:
1. Possibly Helmholtz Resonance in the mouth/throat/reed slot. Again a single frequency, although one you can change in play, and again it might be smeared out a bit by damping. This could be used to single out a specific, strong frequency to do the bending? That's what the 'artificial mouth' experiments maybe imply.
2. Standing-wave resonance in the vocal tract, which can amplify/filter harmonics in the sound and give the timbre.
I do get what you are suggesting about the guitar body, that the different shapes in the body might give different Helmholtz Resonances frequencies from the one body of air. It's just that I cannot find anything that suggests that can happen. If it is a real thing then, honestly, absolutely, genuinely I'll accept it.
Last Edited by MindTheGap on Mar 10, 2017 8:11 AM
I must say that before I started with the harp, I never thought much about Helmholtz Resonance, other than knowing it was a thing, had a single frequency, and gave particular effects like blowing a note from a bottle and unpleasant throbbing in the car when someone has a window open just so.
When I read it was responsible for bending, that seemed plausible, because of the strong, single frequency resonance. Then then I read everyone saying it is responsible for everything, and I'm thinking, hang on, surely the harp can't be that singular can it?
