Your breath does not "flow through" the flute - Physics vs Rumi

[uday_shankar]

Physics vs Rumi !

https://youtu.be/8_nr0IVBSrw

[uday_shankar]

FLUTE PHYSICS vs RUMI - part 2 (skeptics' version)
There were doubts raised, not of great merit, about the earlier demo, regarding the length of the tube, "air escaping through the holes", etc, etc. To lay to rest any doubts, I fashioned a holeless mini-quena out of a brass pipe, where the breath can only "escape", if at all, through the end of the flute or along the length of the pipe. As can be seen there is only a flutter but the flame is not blown out, the reason being that there is no breath flow at the flame in spite of a long steady note being blown straight at it.

https://youtu.be/HYPlTFVC0jo

[Nick H]

You could have demonstrated without making anything, although that might have been less satisfying!

Blow across the top of a bottle.

Without even trying to play one, I think that people ought to be able to see that flautists do not blow into the flute, they blow across that hole.

Uday, isn't the passage of air from mouth into the instrument (where it happens) incidental anyway? Take a reed instrument. Or even a brass instrument. Air must be passing into and out of the tube, because lips are closed around it and there is nowhere else for it to go. It's the vibrating column of air that makes the sound, not the passage of it.

I'm not a musician or physicist: am I right?

[uday_shankar]

You could have demonstrated without making anything, although that might have been less satisfying!

Blow across the top of a bottle.

Without even trying to play one, I think that people ought to be able to see that flautists do not blow into the flute, they blow across that hole.

Uday, isn't the passage of air from mouth into the instrument (where it happens) incidental anyway? Take a reed instrument. Or even a brass instrument. Air must be passing into and out of the tube, because lips are closed around it and there is nowhere else for it to go. It's the vibrating column of air that makes the sound, not the passage of it.

I'm not a musician or physicist: am I right?

True Nick but note that bottle case is not exactly analogous to the quena (Andean flute) as it is sealed off at one end. Technically the bottle is a "closed pipe". It is an exact analog to a pan flute. Other than than the blowing and the air not "flowing through" is the same ! But listen to this, even after demo 1, some folks on social media couldn't get it out of their heads that somehow the air that you blow "into" the flute is somehow channeled through the various holes and that's what makes the "notes'. Hence the need for the second demo above!

As regards reed instruments like clarinet, nagasvaram, oboe, etc the operations is a little different. At the outset, yes some air does flow through them. But as you say that too is not responsible for the sound and you only blow through the reed to provide the vibrational stimulus for the resonance or the formation of the standing wave, in the pipe. Pipe physics takes care of the rest. Of course since it is a closed pipe the fundamental mode is a quarter wavelength as opposed to half wavelength in the flute. Thus for approximately same column length (distance from mouthpiece to the first open hole, in a first approximation) the clarinet will produce a note about a fourth lower. I can work out the math but why belabor this.

[Nick H]

It is one of those things that, I suppose, "stands to reason" that air must blow through a blown instrument and carry the sound. And people like their "reason."

For you, who have researched the maths, the physics and the practical, there is a different set of "reason." The right one, of course.

Even for me, I learned the basics when I tried to make some simple music with a recorder, sixty years ago. Is it called an "edge tone?" And why does that edge make sound? Baby talk, please: no maths!

[uday_shankar]

Is it called an "edge tone?" And why does that edge make sound? Baby talk, please: no maths!

Indeed, it is called an edge tone for precisely the reasons you mentioned. However neither the edge nor the player's breath "makes the sound" directly but all of these have to come together to create a complex motion of air near the embouchure hole that stimulates the pipe into resonance/standing wave formation. Hence it is the resonating pipe that "makes the sound". Its length determines the frequency or pitch. The stimulus or "forcing function" for the pipe can be a variety of things:
1. Physics Lab tuning fork placed near the mouth
2. Flute player's breath meeting the edge
3. Clarinet or nagasvaram players blowing through parted reeds and exciting them into vibration
4. Lips of the brass player vibrating at the trombone's/trumpet's cup-like mouthpiece

[Nick H]

Thanks. Just a small thing about what's "obvious" to people...

Bananas.

Which way do they grow?

Almost everybody outside countries where we see them growing regularly will hold the stalk up and let the fruit hang down. Stands to reason, right?

[Vayoo Flute]

You don't even need to blow through a flute to point this out! Just take a flute and put the blowhole next to one ear. You will hear a note. Turn on a tambura nearby tuned to the first open hole. You will hear the flute playing by itself even more clearly. Manipulate the finger holes as if you are playing, and you will hear all the notes, despite being faint. The fact is that a flute plays all the time. It is resonating with the stray frequencies surrounding you.

[uday_shankar]

point this out!

Not clear what you mean by "point this out".

In order to point out that one's breath does not "flow through" the flute as commonly imagined, we absolutely have to blow the flute and somehow show that in fact it doesn't. That is the only stated intent of the video.

[Vayoo Flute]

Only to "point out" that even without the breathing, the flute plays by itself and although there is a little bit of breathing that passes through the tube (as evidenced by the flicker that you demonstrated), that is not what creates the notes heard.

[uday_shankar]

Only to "point out" that even without the breathing, the flute plays by itself and although there is a little bit of breathing that passes through the tube (as evidenced by the flicker that you demonstrated), that is not what creates the notes heard.

No sir, I request you to please watch the video again. I clearly state that the flicker (or flutter is the word I use in the video) is due to the extension of the standing wave itself beyond the mouth of the tube, which has sufficient amplitude (i.e. before they dissipate as plain sound waves) to create a flutter. I make it clear specifically and emphatically it is not due to any "little bit of breath passing through" the flute. If you wish to disagree with that and insist that breath passes through, please say so. Also please watch the second video with a short pipe.

Secondly, it is the complex motion of the breath near the embouchure hole that provides a stimulation to the formation of
standing waves resonances of sufficient amplitude to be audible. That the air column has a natural standing wave frequency is determined by well known physics which we don't need to belabor. When we put a ear to the hole, we are hearing the natural standing wave frequency of the column. The stimulus for this comes from small random perturbations in the air around us. The atmosphere is full of white noise. It take extremely small amplitudes of acoustic pressure, in the order of a microPascal, for sound to be audible from an object placed at the ear. The stimulus required to create this amount of acoustic pressure is sufficient from extremely tiny random perturbations of air. So yes you will always hear the natural frequency of a pipe if you stick the ear to its mouth. Flute operation is to make it audible by way of blowing at the embouchure hole.

[shankarank]

If breath indeed passes through only there will be breath and no wave

OK a serious one : Heard recently in a TNS Lecdem on youtube (done somewhere in Kerala), that the default full open configurations produce Harikambodhi scale. So he concludes that tamizh isai ( or isai tamizh) developed based on the Flute sound!

Here is a Flute Raman video that demonstrates the notes : https://www.youtube.com/watch?v=njrktdMAZhg

Now how do we explain the physics of the notes Vs. the open/closed holes?

On another note: May be kambu osai became kamboji , and became kambodhi. So there, the rAgA name etymology.

[uday_shankar]

Now how do we explain the physics of the notes Vs. the open/closed holes?

A simple way to think about this systematically is as follows:

1. The flute obeys open pipe resonance physics
2. The two "open ends" of this open pipe, in a first order approximation ignoring cross fingering, are the blow hole and the first open finger/tone hole. If all finger holes are closed, then it is the end of the flute. So we have two ends always open to the atmosphere, always at ground pressure (atmospheric).
3. The distance from the blow hole to the first open hole or the end of the flute, whichever the case, is the vibrating length
4. Because both ends are open and always at ground state, whatever pipe resonances there are will always have a pressure node (i.e. zero acoustic pressure) at the ends, and conversely always have a displacement antinode. Consequently, at the lowest mode or fundamental, we could have a pressure antinode at the midpoint of the vibrating length, thus making up a half wavelength or lambda/2. Nothing simpler is possible. You can visualize this schematically as the familiar bow shape.
5. If L be the vibrating length, then the resonant frequency of the note in question is f = v/λ = nv/2L when v is the speed of sound in air and n is the harmonic number and λ the wavelength. For the fundamental mode n = 1 and hence f = v/2L. There is some nonsense called end correction depending on the diameter which we will ignore in this discussion
5a. The wavelength and frequency are related by the equation v = f*λ.
6. Thus far we have explained until the frequency of any fingering but haven't explained what stimulates the resonance or standing wave at the frequency corresponding to the calculated wavelength
7. So that happens due to a complex interaction of the dynamics of air flow at the mouthpiece/blow hole and the rest of the pipe. A simple and incomplete and flawed but satisfying way to visualize it is that blowing creates a swirling motion of air at the mouthpiece and when the revolutions per second of the swirls match the standing wave frequency in Hz, the flute spontaneously resonates. So it all depends on the velocity of the jet of air that the player ejects from his/her mouth and constantly modulates that jet velocity as he/she traverses the notes. Of course if any flute player learns that he/she is constantly changing the veolcity of the jet he/she may be too gobsmacked to continue playing, having prided himself/herself about the "steady" breath. The fact is there is something like a steadiness of breath over and above all the modulation !

[uday_shankar]

The phrase "vibrating length" is inappropriate when speaking of air columns. We should use the term "resonant length" in its place. "Vibrating length" is more appropriate for strings, for example in a vina.