Blowing machine

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trill
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Thu Mar 30, 2023 5:31 pm . . . I don't know if some capacity added to the system (eg a 2 litre plastic milk bottle) might slow some of that down....
Very interesting idea. Capacitors certainly smooth out the pulsations coming out of rectifier circuits !

Would you wire it series or parallel ?

Maybe wrap some duct tape around it to damp out bulk-mode oscillations.
trill
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Wed Mar 29, 2023 5:49 pm . . . Interesting to listen while doing it. With the long tube, not much sound issueing. As the tube is shortened, the sound gets louder and shriller.
The area of the tube (13.5mm dia) is ~11x the calibrator (4mm). So, once the flow has fully developed in a long tube, the velocity will be much lower (9%).

I think it's the velocity that produces the sound waves.

As the tube gets shorter, more and more higher-velocity flow creates the eddies, giving the sound pulsations.
Last edited by trill on Thu Mar 30, 2023 11:28 pm, edited 1 time in total.
trill
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Re: Blowing machine

Post by trill »

trill wrote: Wed Mar 29, 2023 1:13 am I'm wondering now about the role of entrainment . . . Reminds me of "added mass" for underwater bodies. It gets dragged along. . . I'm wondering if that "dragging" adds resistance. . . Speculation, of course.
Thought experiment: if you push a steel rod into maple syrup, you'll feel resistance from the drag.

In our case, the "rod" is the jet of air from the calibrator.

So, can the mixing/entrainment act like resistance ?

Well, the "information" or "feel" can propagate back (**) at the speed of sound, ~300 m/s. Compared to 27 m/s of the 20l/m flow.

I'm warming to the idea . . . still pondering though . . .

One thing for sure: all 3 measurement sets agree with a steady drop in pressure over the first 50mm of tube-overhang.

The question is: why ?

(**) Heaven forbid: Backpressure !
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Re: Blowing machine

Post by david_h »

How about an artificial mouth to give a reservoir at the inlet end, like Fabre et al with their recorders?

There probably isn’t much energy in that sound, but making the sound might use more. Energy loss = resistance. What’s its spectrum like? Vortices from an orifice (i.e no edge) when we whistle with our lips are tuned with our mouth cavity** but the tube beyond the jet as resonator might also serve. Or is the sound just being muffled and filtered down the tube?

** So you can push a piece of string in that context.
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Terry McGee
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Re: Blowing machine

Post by Terry McGee »

I wondered if we already have an artificial mouth in the form of the Whistle Connector? It's about 80mm long and 13.3mm bore. That gives it a capacity of about 11mL (just over 2 teaspoons!) (and not including the capacity of the thinner tube that feeds it from the Air Flow meter.

Whereas Google tells us the human mouth has a capacity of 55mL for women and 71mL for men. But I wonder if that is with a gobful of air or whiskey, rather than with the mouth in whistle-blowing shape? Did these recorder investigators give a volume for their "mouth"?

And I tried out a spectrum analyser on the noise emanating from the setup:
- Calibrator only: white noise plus a peak around 5K (flow 20L/Min, pressure 70mm)
- Calibrator plus about 47mm overhang of tube: white noise plus peaks at 1.8K and 4.8K (flow 20L/Min, pressure 63mm)
- Calibrator plus about 120mm overhang of tube: white noise plus peaks at 750Hz and 4.7K (flow 20L/Min, pressure 62mm)
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Re: Blowing machine

Post by david_h »

So maybe something to do with the jet at 5Hz that changes only slightly as tube is added plus something about right for a closed pipe resonance from the tube.

Can your ear detect the 5Hz tone or is it lost in a hiss of white noise? Blowing the wrong way through whistle windways sounds like a hiss to me but I'll have a look at the spectrum later.

I was the 13.3 mm bore at the beak I was wondering about. Earlier on Tunborough seemed happy that it was a large enough diameter for his modelling but that was before weird things were found at a change in diameter at the other end. Though I suppose the recorder guys, with a wide range of beaks, didn't have the simpler option of stuffing them into the same tube.
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Terry McGee
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Re: Blowing machine

Post by Terry McGee »

Note I said 5K, not 5Hz. Sorry for using the vernacular 5K, I should have used the formal 5KHz. And I wouldn't describe it as a 5KHz tone, more as white noise with a shallow peak in the noise showing at 5KHz. Slightly tuned noise, if you like.

You can experience the sort of effect I'm hearing with this easy simulation. Draw your mouth into a smile, and say a long "shhhhhhhhhhhhhh...". Now do it again while slowly extending your mouth into a pout. The apparent pitch drops, but it's tuned noise, not a clear note.

You can do the same illustration by pressing the window of a whistle up to your lips and saying the "shhhhhhhhhh" into it, while fingering the scale. Tuned noise.

Looking at the effect of adding scraps of tubing, I'm imagining that we're seeing a quarter wave tuning effect. Flutes and whistles are normally half-wave, as the tube is effectively open at each end, but the 30 by 4mm Calibrator and a lot of resistance upstream possibly presents more like a closed end. The 120mm overhand would thus imply a 480mm wavelength, about 715Hz, near enough to the 750Hz peak I saw. And the 47mm overhang would imply a 188mm wavelength, about 1824Hz, near enough to my 1.8K peak. Plausible?
trill
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Mon Apr 03, 2023 4:33 pm . . . Plausible?
Entirely plausible.

Very nice summary. Makes me think of "band-limited" noise.

I had a colleague once who studied "low-noise" flow control valves. If I remember correctly, noise is proportional to "(peak-velocity)**8". Yes, that's the eighth-power.

There are "low-noise" flow control valves. Prices are very high compared to simpler versions.

One low-cost way to keep noise down is to use a clamp on an elastic tube-segment.
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Terry McGee
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Re: Blowing machine

Post by Terry McGee »

A long time ago....
Terry McGee wrote: Wed Mar 08, 2023 11:59 pm Tunborough, you mentioned some way back that you'd like to see data from a head with a longish blank tube and the same head with a shorter blank tube. I delved into my brass tubes division and found it emaciated in the extreme. Best I can offer at the moment would be a 237mm long and a 141mm long length of 12.64/11.9mm tubing. This tubing will fit the Old Gen, New Gen, Feadog Mk1 and Killarney heads. Any good to you? Which head? Same 4L/Min increments? Tubing pushed all the way into the head, or leave a typical and equal gap in both cases?
Tunborough wrote:Those tubes should work nicely, as long as you don't mind going high and loud with the short one. Let's start with the Feadog mouthpiece, with the tube pushed all the way in. I'll want to know what the length ends up between the splitting blade and the end of the tube. For this, remember, we're measuring frequency as well as flow and pressure, going up as high as you dare, and back down again, to test the limits of the hysteresis in the register shifts. Because we want to get as close as we can to the register shifts, we can't limit ourselves to fixed intervals like 4 L/min.
So I've just done it on the longer tube on the Feadog Mk 1 Head. The bottom of the first regime is too wafty to get a real fix on. And the top of the 4th regime needs more flow than our flow meters can handle. You can certainly see a lot of hysteresis in the flow and pressure columns. EG I can push the top of the 2nd Regime to 22L/Min, but then drop the bottom of the third to 17.6L/Min.

With all the noise, and the flip-flopping between regimes, it is a bit bewildering running these tests, so I won't be surprised if I got some of it wrong. Feel free to be harsh!

Code: Select all

Feadog Mk1 with 244mm blade to end of tube, 4 April 2023			
Regime	Flow	Press	Hz
Bot 1			Wafty
Top 1	10.9	20	647
Bot 2	11.8	23	1242
Top 2	22	75	1296
Bot 3	17.6	52	1865
Top 3	34	182	1947
Bot 4	25.5	106	2505
Top 4	>40	370	2602
Is this useful? Is there more data you want collected? How do you want the results presented? Should I do the shorter tube?
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Re: Blowing machine

Post by Tunborough »

Terry McGee wrote: Tue Apr 04, 2023 1:07 am Is this useful?
Absolutely!
Terry McGee wrote: Tue Apr 04, 2023 1:07 am Is there more data you want collected?
Lots.

From those numbers and measurements on a Feadog here, I would have thought the tube was a hair longer, more like 245 to 245.5 mm from blade to open end. Is this a possibility?

We're seeing overlap (hysteresis) between the second and third regimes and third and fourth regimes, but not between the first and second. What's happening between 10.9 and 11.8 L/min?

Can you fill in data points between the top and bottom of each regime, please. The goal here is to be able to plot frequency as a function of air speed out of the windway, so enough points to show the shape of the curve. The low end of the first regime should be particularly interesting. The format you give above is good.
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Re: Blowing machine

Post by Terry McGee »

Tunborough wrote: Tue Apr 04, 2023 7:28 pm From those numbers and measurements on a Feadog here, I would have thought the tube was a hair longer, more like 245 to 245.5 mm from blade to open end. Is this a possibility?
No, measured more carefully it comes in at 243.6mm. Now, the Window Length is 5.32, I don't suppose I was guilty of tampering with the edge back in the day? We did desperate things back then. We had to!
We're seeing overlap (hysteresis) between the second and third regimes and third and fourth regimes, but not between the first and second. What's happening between 10.9 and 11.8 L/min?
Primal Chaos. Firstly you hear the higher regime starting to sneak in, then it gets warbly, and then the lower regime exits the field. I'm guessing that the warbly effect suggests that at that point the two regimes are not in a simple harmonic relationship. Certainly the Top 1 at 647 is a long way from half the Bot 2 at 1242 Hz!
Can you fill in data points between the top and bottom of each regime, please. The goal here is to be able to plot frequency as a function of air speed out of the windway, so enough points to show the shape of the curve. The low end of the first regime should be particularly interesting. The format you give above is good.
OK, how does this look? I've arbitrarily gone with a total of 5 points per regime, picking round numbers as they are easier to set on the Flow Gauge(s). And avoided going below 6 L/min as I thought we'd cast doubt on the accuracy any lower. But let me know if you'd like me to go lower and by how much (in flow or Hz terms).

Code: Select all

Feadog Mk1 with 243.6mm blade to end of tube, 5 April 2023			
Regime	Flow	Press	Hz
Bot 1	6	5	600
Lo 1	7	7.5	628
Med 1	9	13.5	641.1
Hi 1	10	17	645.2
Top 1	10.9	20	647
			
Bot 2	11.8	23	1242
Lo 2	14	34.5	1268
Med 2	17	48.5	1281.5
Hi 2	19	62	1290.5
Top 2	22	75	1296
			
Bot 3	17.6	52	1865
Lo 3	22	72	1899
Med 3	26	104	1916.5
Hi 3	30	143	1933
Top 3	34	182	1947
			
Bot 4	25.5	106	2505
Lo 4	30	140	2532
Med 4	36	201	2556
Hi 4	40	264	2575
Top 4	>40	370	2602
It will be interesting to see if other whistles follow the same general pattern, or if this one is different for perhaps reasons of voicing.
trill
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Re: Blowing machine

Post by trill »

Terry McGee wrote: Tue Apr 04, 2023 11:52 pm . . . Certainly the Top 1 at 647 is a long way from half the Bot 2 at 1242 Hz! . . .
I was puzzling over the ratios of individual tones in the 1st 2 regimes. I was wondering how the ratio varied with pressure+flow.

My first stab was to lump them together:

The average of all the R1 tones is: 632.26 Hz.
The average of all the R2 tones is: 1275.6

The ratio is: 2.0175

Still puzzling . . . makes me wonder about "octave balancing" in whistles.
Last edited by trill on Wed Apr 05, 2023 12:57 am, edited 1 time in total.
trill
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Re: Blowing machine

Post by trill »

Wasn't sure what basis to use, so simply went with the "Bot, Low, ... Top" ordering (corresponding to 1, 2, .. 5) on the graphs" :

Image

Looks pretty systematic, with possible "sweet spot" of near-exact multiple of 2 at "Med".

So, plotted them all:

Image

Looks like the "low ends" all exhibit the greatest departure from integer-multiples.
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Re: Blowing machine

Post by david_h »

Terry McGee wrote: Mon Apr 03, 2023 4:33 pm Plausible?
Yes, sorry, I wasn't clear that that was what I was suggesting by 'closed pipe resonance'. I slipped up on the Hz because they were the number I was diving 343 by to get millimetres
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Re: Blowing machine

Post by david_h »

When making the shhhh sound with the lips are we tuning noise or selectively amplifying/attenuating parts of it with a resonance in our mouths. So unlike when we whistle with our lips there is no feedback to the jet. Maybe we are also selecting what gets to our ears via our head cavities.
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