Blowing machine

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stringbed
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Re: Blowing machine

Post by stringbed »

david_h wrote: I can’t find it now, but I did find this: https://hal.science/hal-00964988 which seems to be research in the general area your folks are discussing. There is a section headed “Pressure controlled artificial mouth”.
This is extremely worthwhile reading for the description of the measuring instrumentation alone. The conclusions based on the experimental data — all expressed in terms of air pressure — will otherwise be no surprise to anyone here. Digital manometers normally permit pressure measurement at two points. On a whistle, the oral cavity is the obvious and accessible one, and the point of comparison would be somewhere inside the bore. The article indicates where that might usefully be, but getting there to measure it is invasive.

The tuners and voicers at Moeck had access to a blowing machine that was essentially what we’ve been talking about designing here. The air feed was set volumetrically and the air pressure was measured at the entrance to the windway. I never saw or heard of anyone using it the entire time I was there. We also all had water-column manometers at our workbenches and used them for such things as calibrating differences between our individual blowing pressures and logging what we did when custom tuning for VIP clients.
trill wrote: 4) One question I have is what role the human anatomy (mouth cavity, throat, lung volume) have on the “total acoustic field”.
Tunborough wrote:That we don’t know yet. There is something happening, because skilled recorder players have more control over frequencies around the register shift than novices.
I studied the recorder with Bernard Krainis for several years. One of the techniques that he taught — labeling it as counterintuitive but effective — was how to maximize and vary the size and shape of the oral cavity. He said he based it on watching the way Frans Brüggen played and confirmed in discussion with him, that Frans was consciously harnessing the effect. A quick check a few mins ago showed that the pressure in the cavity drops as it is enlarged. The effect on tone quality is perceptible without any shift in pitch, which I assume means an instinctive increase in air flow. There was no immediate indication of any of this making a diff when shifting modes of vibration but I’ll spend more time with that.
Tunborough wrote:What I want to do is measure the output frequency of the whistle as the flow is varied. What’s the frequency at the lowest flow at which a note just speaks? What’s the highest frequency just before a note jumps to the next register? What’s the lowest frequency in the second register before the note drops down to the first register? How does the frequency vary with flow between these extremes? With this information, we can design a whistle that stays in tune with a regular increase in breath flow as we go up the scale.
An automated blowing device may be useful for measuring the steady-state behavior of a whistle. However, it would also have to emulate the initial transients of notes bumped into different registers as done by a reasonably skilled actual player. Repeating what I still feel to be a pivotal question — given that so much of the available data is quantified in terms of pressure, and that any one of us can measure that aspect of their own playing, what purpose is there in shifting to volumetric data? Terry’s chronicle of his on-going efforts is informative and fascinating, and it is easy enough to understand the L/min measurements in relative terms. But it would sure be nice to be able to compare them in a more absolute sense, for example, to the workshop literature about voicing organ pipes.
Last edited by stringbed on Fri Jan 20, 2023 3:52 am, edited 1 time in total.
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Re: Blowing machine

Post by hans »

stringbed wrote: Fri Jan 20, 2023 3:04 am An automated blowing device may be useful for measuring the steady-state behavior of a whistle. However, it would also have to emulate the initial transients of notes bumped into different registers as done by an actual player. Repeating what I still feel to be a pivotal question — given that so much of the available data is quantified in terms of pressure, and that any one of us can measure that aspect of their own playing, what purpose is there in shifting to volumetric data? Terry’s chronicle of his on-going efforts is informative and fascinating, and it is easy enough to understand the L/min data in relative terms. But it would sure be nice to be able to compare it in a more absolute sense, for example, to the workshop literature about voicing organ pipes.
I agree. Terry, perhaps you could add pressure measurement data to your flow data, so we can see some relationships, and be able to replicate experiments with simple pressure measurements?
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Re: Blowing machine

Post by Terry McGee »

I'll have a look at it, hans. The setup is a bit messy, but let's see if it can handle getting messier!

Now, here's today's Frightening Fact. If I calculate correctly, the volume of a 12mm bore tin whistle is just over 30mL. But in doing these tests, I've been pumping an average of about 15L/min through it. That's 15,000mL, or about 500 air changes per minute. That's 30,000 air changes per hour. Convince me I'm wrong!
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Re: Blowing machine

Post by stringbed »

The air flow is split at the edge. The illustrations I’ve seen of the process show the larger part diverted to the outside of the instrument.
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Re: Blowing machine

Post by david_h »

A quick look at the maths and physics of gas flow through orifices suggests you need to measure both pressure and flow for the various windways.

What is the effect of 'forming an embouchure' with the lips on a whistle? Injecting turbulent air into windway? Does it really effect tone? Does tonguing briefly change the nature of the airflow arriving at the windway?
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Re: Blowing machine

Post by stringbed »

Quoting david_h:

“What is the effect of ‘forming an embouchure’ with the lips on a whistle?”

I would guess none but if we’re going to take measurements to provide an objective answer, there’s going to be more than air pressure and volume to them.

“Injecting turbulent air into windway?”

The purpose of the windway is to transform what is presumably turbulent input into a reasonably uniform laminar flow.

“Does tonguing briefly change the nature of the airflow arriving at the windway?”

Tonguing is not a homogeneous concept but, to a first approximation, serves to interrupt airflow. Modulating that effect is an important aspect of the playing technique. For present purposes, it is no more or less significant and tractable a factor than the onset of an unarticulated test run.
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Re: Blowing machine

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stringbed wrote: Fri Jan 20, 2023 3:04 amRepeating what I still feel to be a pivotal question — given that so much of the available data is quantified in terms of pressure, and that any one of us can measure that aspect of their own playing, what purpose is there in shifting to volumetric data?
My interest right now is steady-state tuning. The physics says that steady-state tuning depends on the air speed across the window. As I said earlier, translating volume flow to air speed (at the windway exit, at least) is much more direct than translating air pressure.

Transient effects are musically significant, but not relevant to my immediate interest in steady-state tuning.
Terry McGee wrote: Fri Jan 20, 2023 4:50 amThat's 15,000mL, or about 500 air changes per minute. That's 30,000 air changes per hour. Convince me I'm wrong!
stringbed wrote: Fri Jan 20, 2023 5:02 am The air flow is split at the edge. The illustrations I’ve seen of the process show the larger part diverted to the outside of the instrument.
A simple feather test suggests this is true: much more air comes directly out of the window than out of the end of the tube (and then when you add in a bunch of open toneholes ...).
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Re: Blowing machine

Post by Tunborough »

It looks like typical modest-price flow meters, like Terry's, measure up to 20 L/min, maybe 25 L/min. I did see a pricier line of meters that went up to 70 or 100 L/min. I figure we need up to 30 L/min to test a high D whistle, and maybe 60 L/min or more to test the second octave of lower, more air-hungry, whistles. So, does anyone know of a good source for flow meters of reasonable price and higher range?

It does surprise me that we are pumping more air through our little whistles than typical users of these flow meters are dealing with. If we didn't have Terry's numbers, I'd be seriously questioning my estimates.
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Re: Blowing machine

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Tunborough wrote: Fri Jan 20, 2023 8:33 am The physics says that steady-state tuning depends on the air speed across the window. As I said earlier, translating volume flow to air speed (at the windway exit, at least) is much more direct than translating air pressure.


The direct measurement of the relevant quantity is always to be preferred over a derived value. In this case, the former is not available and there is a choice of two quantities from which the derivation can be made. There is a body of relevant reference data expressed in the one of them and nothing that has yet been cited here that uses the other. I really don’t want to belabor this but will ask one final time, what exactly do you mean by “more direct translation” and what insight does operating on volumetric data generate that is not to be had within the established manometric frame of reference?
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Re: Blowing machine

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stringbed wrote: Fri Jan 20, 2023 11:42 amwhat exactly do you mean by “more direct translation” and what insight does operating on volumetric data generate that is not to be had within the established manometric frame of reference?
From volume flow, we use simple geometry:

air speed at windway exit = volume flow / area of windway exit

Whereas from pressure, we have to use Bernoulli's equation. With a bunch of assumptions, I think we get something like ...

air speed = sqrt( 2 * pressure in mouth / air density + speed in mouth ^ 2 )

Air density depends on temperature and humidity. Perhaps we can assume the air speed in the mouth is zero, but if we're feeding the whistle with a narrow tube that may not be a safe assumption.
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Re: Blowing machine

Post by david_h »

There was a recent discussion (by you guys) about different windway geometries and almost continuous discussion on this forum about how whistles 'blow' and/ or air requirements. So I think results from an experimental setup recording both volume and pressure would be interesting to many.
stringbed wrote: Fri Jan 20, 2023 6:53 am The purpose of the windway is to transform what is presumably turbulent input into a reasonably uniform laminar flow.
Tunborough wrote: Fri Jan 20, 2023 12:22 pmPerhaps we can assume the air speed in the mouth is zero, but if we're feeding the whistle with a narrow tube that may not be a safe assumption.
If the air-speed of a mouth not 'forming an embouchure' is low the then air going into the windway is presumably not (very) turbulent. Wouldn't it become turbulent (or at least non-laminar in some way) as the speed increased just inside the airway? Maybe experiments with a windway connected directly to a large diameter (i.e. mouth-like) pipe and with a short length of pipe with cross-sectionnot much different to the windway area (i.e. embouchure-like) (so the air had already accelerated would give different results.
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Re: Blowing machine

Post by Terry McGee »

Woah, a lot of thinking going on while I've been asleep! I have some catching up to do!

I've been musing on "the things that could go wrong" in all of this. For example, noticing that when I put the two flow monitors in parallel, they don't share the flow quite equally. This could be for a number of reasons, but needs to be checked out. For example, does it imply the two meters do not agree? Or just that the lengths of tubing and therefore the resistances feeding them are different? Or both, or other?

To test the agreement of the flow monitors, I put them in series (daisy chain) and cranked up the flow so one of them showed 20L/min. The other read around 19.3L/Min (as best as you can interpret its short scale). So that's about 3.5% disagreement. Probably not a knock-out blow?

That doesn't tell us that either is accurate. It would be nice to be able to recalibrate them from first principles, which might be possible.

I'd be pretty confident that the length of tubing feeding both monitors when in parallel is going to need tweaking to improve their sharing. Unless we replace the pair with a higher capacity monitor. I also have available a Magnahelic low differential pressure gauge, and I wonder about making that into a flow meter. It would give enhanced reading precision and avoid the need for switching monitors. I'd need a calibrated or calibratible resistance, which is probably not to hard to come up with.

We need to consider environmental issues. I'm at about 50 metres above sea level, so that's probably near enough to zero? And workshop temperature in the low twenties. STP!

But my compressor is providing air, and dried air at that. Our whistles are expecting warm, dank air, oxygen depleted, CO2-enriched. Can we recalculate for that? Or is it near enough? I can perhaps test the difference that it makes to pitch if theory isn't enough.

The tubing I am using has a 1/4" bore (6.35mm), but the joiners and T-joints have a 4.75mm bore. I have plenty of reserve pressure, so resistance is not an issue of itself, unless say when using parallel flow gauges. The whistle I'm playing with has a duct entry of 8.36 x 2mm, and an exit of 8.14 x 1.51, a CSA of 12.3mm2. The CSA of a joiner is around 17.7mm2, so in similar territory.

Any alarm bells there? Or any thoughts?
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Re: Blowing machine

Post by hans »

I don't see a need that the two cheap flow monitors in parallel should both monitor half of the flow, in equal measure. The sum of both is enough. Of course errors will sum up too, and your in series experiment suggests that there are errors in accuracy. Those monitors are functioning by having a ball dancing on a column of air, and the more air flow through, the higher the ball gets pushed, yes? This looks not to be a too accurate method, but it gives us rough figures. The difference of jet speed between low and second octave is most likely very significant, and the testing method should not introduce additional errors for the two scenarios IMHO.
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Re: Blowing machine

Post by stringbed »

”Terry” wrote: I’ve been musing on “the things that could go wrong” in all of this. For example, noticing that when I put the two flow monitors in parallel, they don’t share the flow quite equally.

Any alarm bells there? Or any thoughts?
Have you encountered any similar problems in the measurement of air pressure? Despite my curmudgeonly whining about it, the only reason thus far given for measuring air flow is that velocity can be calculated from it more elegantly than it can from air pressure.
Tunborough wrote: From volume flow, we use simple geometry:

air speed at windway exit = volume flow / area of windway exit
In order for that expression to be of practical utility, the area of the windway exit needs to be quantified. With all the chamfering and block offset that’s been noted in one or another of the threads through which this discussion has meandered, I would have thought placing a number on the exit area to be a daunting challenge all of its own. And we haven’t been talking about using the derived velocity for any specific purpose beyond noting that, as in any edge-blown system, frequency varies directly with it.

Placing this in another perspective, when the time comes to calibrate the behavior of our blowing machine by putting a whistle designed with it into the hands and mouth of an actual player, which methods of measurement are we going to to employ? Measuring air pressure is easy enough in a dynamic playing situation. I have a rough time envisioning how the volume of the expended air might be tracked.

I realize that this will trigger another round of “that’s why we should measure both” responses. However, their quantification serves the same ultimate purpose. If measuring the one is vulnerable to the discrepancies that Terry has noted, and the other is less so, why are we insisting on working with more than the single quantity on which all prior reports have been based?
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Re: Blowing machine

Post by Terry McGee »

hans wrote: Sat Jan 21, 2023 3:00 am I don't see a need that the two cheap flow monitors in parallel should both monitor half of the flow, in equal measure. The sum of both is enough. Of course errors will sum up too, and your in series experiment suggests that there are errors in accuracy. Those monitors are functioning by having a ball dancing on a column of air, and the more air flow through, the higher the ball gets pushed, yes? This looks not to be a too accurate method, but it gives us rough figures. The difference of jet speed between low and second octave is most likely very significant, and the testing method should not introduce additional errors for the two scenarios IMHO.
I think that's fair point Hans. My background in scientific measurement and control has probably made me too sensitive to minor inelegances. I will attempt to concentrate on the important!
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