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PostPosted: Sat Dec 29, 2018 4:11 pm 
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Indeed, and I thought that might be an advantage, given most of the suitable available tubing has pretty thin walls. And we don't want to make the outside diameter too great.


Excellent point--I always added a lip plate to my earlier versions of this design, so that would render the plate unnecessary.

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I think trial and error is probably a very good approach. Firstly, we can't assume Boehm got it perfectly right (although it wouldn't surprise me!). But more than that, we don't know how people have dealt with his bore since. He presumably would have been aiming at a lower pitch, like A430. When his work was re-released by Rudall & Carte in England did they just take his bore, or did they retweak it for the high pitch coming into fashion there? And since then have all our manufacturers carefully reworked it for A440 or taken whatever they found as good enough? Given the work Albert Cooper and more recently Trevor Wye have been doing on improving the intonation on Boehm flutes, I would suspect that near enough has been good enough at many times. And of course we're using smaller holes than Boehm had in mind, so that's going to have some effects too. So the DIY approach is good!


I found it interesting that in his book Boehm indicated that he actually preferred the flute to have a 20mm bore instead of 19mm. He compromised and did 19mm because it gave better intonation on the high notes (and it's possible that at least one important note was either unattainable or very, very flat with a 20mm bore), and this was what players wanted. But he thought the tone of the 20mm bore flutes to be nicer in the first couple of octaves.

As for the parabolic taper, I wouldn't be surprised if other makers discovered that it was good enough without much tweaking. I have reamers made to Boehm's specifications that I use for my headjoints (the very specs he provided in his book) and they work great. Not only do they work great, but they work great even when the diameter changes due to wood mobility. Boxwood is super prone to shrinking, for example. In fact, at one point I measured a bunch of headjoints (both metal and wood) from makers such as Cooper, Arista, Haynes, Powell, Altus, Brannen, Muramatsu and the amazing David Chu, whose wooden headjoints are considered to be among the best available. David's was amazing sounding (happened to be boxwood) and when I measured the bore it had clearly shrunk quite a bit, and yet it was superb. It differed quite a bit from the metal headjoints that had not shrunk at all (obviously), but I think it was nicer than most of them. I've seen the same thing with variations in my own headjoints, so I think that taper is pretty forgiving. As long as you start with an accurate reamer and reasonably stable material, even with mild distortion it still performs just fine.

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PostPosted: Sat Dec 29, 2018 5:18 pm 
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Yes, I've been intrigued by the notion of a conical flute based on a 20mm head bore ever since reading that back in the seventies! So I'm looking over Tunborough's shoulder with the thought that WIDesigner might prove the appropriate tool to model the rest of it.

And I think you are right - for some reason the Boehm bore doesn't seem very touchy. But then how did Boehm conclude that it should have the bulge we've been talking about? Again WIDesigner might enable us to replicate Boehm's physical experiments.


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PostPosted: Fri Jan 04, 2019 5:43 am 
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There's a precedent for this in the uilleann piping world: "rushing" a chanter to adjust the tuning. Has anyone ever considered using a helical coil (stainless steel wire or some other volume-filling material) in the headjoint to occupy the space, with a progressively tighter helix toward the stopper, and the helix coiled in the natural direction of airflow (clockwise down the tube)?


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PostPosted: Mon Jan 07, 2019 9:34 pm 
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Well, I've got some results from modelling headjoints, and they are quite unexpected. I modelled a few flutes with cylindrical bodies, some 19 cm diameter, and some 20.5 cm diameter (3/4" PVC), with a few different hole geometries. I asked WIDesigner to lay out a headjoint around 120 mm long, giving bore diameters every 20 mm plus the stopper position, that would optimize tuning through two diatonic octaves, D4 through D6, plus cross-fingered C-nat for most trials.

If given enough latitude to choose the bore profile, WIDesigner suggests a headjoint that expands in the bottom 20 mm, contracts again to a bit less than the main bore diameter, expands again below the embouchure hole, then contracts again to the stopper. Often, there is no headspace at all; the stopper is right up against the embouchure hole.

If the headjoint diameter is constrained so it can't expand from bottom to top, WIDesigner suggests a 40 mm long taper around the middle of the headjoint, with a change in diameter of maybe 1 mm. Above and below this tapered section, the headjoint is cylindrical. With the right hole geometry, it is quite remarkable how much this simple tapered section can bring the predicted tuning of the octaves into line. I did try a less-than-optimal hole geometry for which WIDesigner also suggested a sharp taper around the embouchure hole, so the headspace was considerably smaller in diameter.

No sign at all of Boehm's parabolic headjoint. Is there any particular hole geometry you'd like me to try to tease out something parabolic?


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PostPosted: Mon Jan 07, 2019 10:22 pm 
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Tunborough wrote:
Well, I've got some results from modelling headjoints, and they are quite unexpected. I modelled a few flutes with cylindrical bodies, some 19 cm diameter, and some 20.5 cm diameter (3/4" PVC), with a few different hole geometries. I asked WIDesigner to lay out a headjoint around 120 mm long, giving bore diameters every 20 mm plus the stopper position, that would optimize tuning through two diatonic octaves, D4 through D6, plus cross-fingered C-nat for most trials.

If given enough latitude to choose the bore profile, WIDesigner suggests a headjoint that expands in the bottom 20 mm, contracts again to a bit less than the main bore diameter, expands again below the embouchure hole, then contracts again to the stopper. Often, there is no headspace at all; the stopper is right up against the embouchure hole.

If the headjoint diameter is constrained so it can't expand from bottom to top, WIDesigner suggests a 40 mm long taper around the middle of the headjoint, with a change in diameter of maybe 1 mm. Above and below this tapered section, the headjoint is cylindrical. With the right hole geometry, it is quite remarkable how much this simple tapered section can bring the predicted tuning of the octaves into line. I did try a less-than-optimal hole geometry for which WIDesigner also suggested a sharp taper around the embouchure hole, so the headspace was considerably smaller in diameter.

No sign at all of Boehm's parabolic headjoint. Is there any particular hole geometry you'd like me to try to tease out something parabolic?


This is very interesting. I'm not familiar with WIDesigner, but your findings remind me of the "optimized" Chinese xiao that was designed by Yan Lang at the University of British Columbia. I spoke of this elsewhere but he created an optimized bore that was a series of these expanded and contracted sections. The nature of the shape made it's creation impossible unless it were cast or molded somehow, since it could not be conventionally drilled or reamed out. I opted for casting.

A friend of mine is a math professor at a Vermont university (and an amateur flute maker) and he passed this data on to me. He is also experimenting with headjoints for the xiao and some of his theoretical models resemble what you've created. A sort of "undulating" bore profile that does not taper.

This seems to show that the "optimal" acoustic shape for some of these flutes might be quite different from what we are used to. But of course, it is easy to see why such bores are not really feasible with wooden instruments. Whether 19th century flute makers like Boehm were hep to these unusual bore designs would be interesting to know, but they obviously didn't choose to attempt them. Possibly the parabolic taper is the best (most optimal) design that can be created using conventional methods (drawn metal tubing or reamed wood)?

It would be cool to try to make the headjoint you describe and see how it performs.

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PostPosted: Tue Jan 08, 2019 3:26 am 
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Woah, very interesting indeed. As I said, "we can't assume Boehm got it perfectly right". But equally, we can't assume WID got it right either, given it's pretty early days yet in its application to transverse flutes. But we owe it to everybody to find out, and, whatever we find, to progress it from there.

Tunborough, are you planning to do anything physical or should we detail somebody else to have a shot at it? Geoffrey? Anybody?

The kind of shapes Tunborough has mentioned are a bit out of our usual comfort zone, but I bet we could find ways to achieve or at least approach them, even if it requires inserting some separately turned and bored sections.

It's sobering to remember that if WID found that with the fiddling-the-head-bore approach, it might come up with some equally interesting suggestions for our older fiddling-the-body-bore approach.

I often have wondered how many of the older 19th century flutemakers gave the game away once the Boehm bore flute started rising into ascendancy. Maybe it's now time for oldies like me to be making my way quietly to an exit? Surely, at 71, I'm too old for change?

Nah, bring it on!


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PostPosted: Tue Jan 08, 2019 7:08 am 
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Terry McGee wrote:
Woah, very interesting indeed. As I said, "we can't assume Boehm got it perfectly right". But equally, we can't assume WID got it right either, given it's pretty early days yet in its application to transverse flutes. But we owe it to everybody to find out, and, whatever we find, to progress it from there.

...

It's sobering to remember that if WID found that with the fiddling-the-head-bore approach, it might come up with some equally interesting suggestions for our older fiddling-the-body-bore approach.
Agreed, on all counts.

Now, Boehm was dealing with two things that I didn't include: extra toneholes to give all the accidentals, and notes up through the third octave. Either of these could change the outcome.

Terry McGee wrote:
Tunborough, are you planning to do anything physical or should we detail somebody else to have a shot at it? Geoffrey? Anybody?

The kind of shapes Tunborough has mentioned are a bit out of our usual comfort zone, but I bet we could find ways to achieve or at least approach them, even if it requires inserting some separately turned and bored sections.
Even if I was able to physically realize these flute designs, I wouldn't have the playing skills to judge the outcome. I am tempted to try something of the sort on a whistle.

The complex, expanding and contracting, headjoint would be a huge challenge, but with the right flute, the contracting-only headjoint would be as simple as sliding in a cylinder of 0.2 mm mylar down the headjoint for 60 to 80 mm, ... WIDesigner predicts there would be no perceptible difference in the tuning of the two headjoints. (Tone colour is another matter, but I'd have more confidence in the sonic consistency of the simple headjoint over the complicated headjoint.)


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PostPosted: Tue Jan 08, 2019 10:15 am 
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One interesting aspect of the optimized xiao that I made to Yan Lang's specifications was that in order for it to work properly, many other factors apart from the bore had to be changed.

On a traditional xiao, the bore is cylindrical, the finger holes are uniformly sized and fairly uniformly spaced in two groups (not including the thumb hole). Wall thickness is the same throughout. The holes are slightly ovaled, which seems to contribute to better intonation, helping to bring the second octave to pitch a bit better. As I've commented before, it is a very sophisticated and functional design. It has some small weaknesses (like most wind instruments) but overall it's very solid.

BUT...the "optimized" version, in order to complete it's optimization, had not just the undulating inner bore, but the outside had to undulate as well! The size and placement of the holes was no longer as uniform, and the wall thickness had some variation. Not a ton, but in order for the wall thickness to remain reasonably consistent, the outer diameter had to mirror the inner diameter. This makes the manufacture of it (from wood with a cast bore) very tricky. It was dangerously thin in places, causing whip if put on the lathe and a host of other difficulties.

And the part that makes me curious about doing some similar redesign of the Boehm headjoint is: will the supposed "gains" be on par with those of this optimized xiao? It was undoubtedly done with a deep understanding of acoustics, using advanced computer modeling and a highly sophisticated prototyping process (see link below), but my point is that the result of the optimization wasn't really that impressive compared to the traditional design. I'm being redundant for those who have read my comments on this in another thread, but the result of the optimization was a xiao that no longer sounded like a xiao. It did seem to have somewhat more uniform tone (in terms of strength from note to note), the intonation was a bit more on target without having to do much tweaking, and it did improve the C natural note (which is weak on a xiao, just like on the Irish flute). But in the process, the timbre of the instrument changed and it actually became more difficult to play. Less free blowing, much less stable on the root note. And one serious xiao player (who trained on Boehm flutes and plays Irish flute as well) said "It sounds really badass, but it's too much like an Irish flute now".

So it makes me wonder (especially when it comes to world flutes from different cultures) whether acoustic optimization erases some character in exchange for these improvements. And as such, are they really improvements? Will all optimized wind instruments end up sounding the same? I'm curious. The Boehm flute seems to work remarkably well in it's present form, and will a different headjoint design make it better, or simply different? Same applies to conical bore flutes, of course. For the people who love them, how much improvement would be desirable if the cost is an alteration of the instrument's character?

Terry, Tunborough and anyone else interested in flute acoustics and in checking out a very impressive bit of research should see this:

https://open.library.ubc.ca/cIRcle/collections/ubctheses/24/items/1.0167080

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PostPosted: Tue Jan 08, 2019 12:49 pm 
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Geoffrey Ellis wrote:
Terry, Tunborough and anyone else interested in flute acoustics and in checking out a very impressive bit of research should see this:

https://open.library.ubc.ca/cIRcle/collections/ubctheses/24/items/1.0167080
Impressive, indeed. Thanks for that, Geoffrey. I hadn't seen it before. Lan's methodology was very much like what we've done in WIDesigner: a transfer matrix model using the tonehole model from Lefebvre and Scavone, with an empirical mouthpiece model. One difference stands out after a quick skim: his optimization runs took hours or days on a large cluster computer; the optimization runs for the headjoint took WIDesigner maybe 15 seconds each on my laptop. At least part of the difference is being more selective about what we're asking the optimization to do.


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PostPosted: Tue Jan 08, 2019 5:25 pm 
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Tunborough wrote:
Even if I was able to physically realize these flute designs, I wouldn't have the playing skills to judge the outcome.

OK, then one of us should, and unless somebody else puts their hand up, it might as well be me. It doesn't sound hard.

Can you tell us the type and the ID and OD of the 2 samples of tubing you've been basing it on, or at least the one you would prefer to start with. First job is to see if I can procure some around here. Failing that, can I come back to you with an ID and OD of a tube I can get, and get you to recalculate?

Alternatively, I notice I have some bright orange* electrical conduit here 19.65 ID and 24.82 OD. A bit thin for an ideal embouchure, but I could slit and glue an offcut to thicken it. Then it would be a little thick at around 30mm, but I could turn it down to whatever.

Then what's the plan? Do I make two flutes - one a plain cylinder and one with the modified bore? And both to dimensions provided by WID?

Do you want the flute(s) tunable (to set A to 440 and then see where the other notes lie), or non-tunable (to see what we get)? Or we could start with non-tunable, then cut the tube and insert a slide if that has attractions. Or I could start with a piece a little too long, then snip bits off until I get a well pitched low D and we work from there?

*The Auld Orange Flute? https://www.youtube.com/watch?v=gSatdW0EfPU


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PostPosted: Tue Jan 08, 2019 7:49 pm 
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this is so interesting. thank you for the discussion


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PostPosted: Tue Jan 08, 2019 9:06 pm 
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That orange conduit would do the job. It's got an ID and OD in the neighbourhood I was looking at. Do you have something you could use to make a cylindrical insert to reduce the ID to 18.9 mm or so for the top 80-100 mm? Maybe a flexible plastic sheet about 0.4 mm thick?

The place to start would be to cut off, say, 570 mm. Push a stopper in 15 mm from one end, and cut an embouchure hole centred about 10 mm beyond that. I'll leave it to you to decide the length and width--and shape and depth--of the embouchure hole; just let me know what they are. If we say the centre of the embouchure hole is 0, then the stopper is at -10, and the far end of the tube is at 545. We'll probably lop off another 4-6 cm from that end.

Let me know what range of pitches you can get with that tube. For example, by varying your breath, you might be able to play D4 varying between 281 - 291 Hz, D5 between 566 and 586 Hz, A5 between 855 and 880 Hz, D6 between 1150 and 1180 Hz, before the flute switches into the neighbouring register.

For drilling the toneholes, are your drill bits metric or imperial? What's the largest size of tonehole you are comfortable with? How big a finger stretch can you accommodate between T2 and T3, and between B2 and B3?


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PostPosted: Tue Jan 08, 2019 11:49 pm 
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Tunborough wrote:
That orange conduit would do the job. It's got an ID and OD in the neighbourhood I was looking at. Do you have something you could use to make a cylindrical insert to reduce the ID to 18.9 mm or so for the top 80-100 mm? Maybe a flexible plastic sheet about 0.4 mm thick?

Not sure, but if not I could probably turn something. Ah, a plastic folder cover that is 0.38? Also in orange!

So that 80-100mm counted from the top of the tube and so includes the stopper? And the embouchure hole goes through it? Might need to glue it around the embouchure hole to prevent it moving?

Quote:
For drilling the toneholes, are your drill bits metric or imperial?

Metric, and the best ones are at 0.5mm intervals. EG 5, 5.5, 6 ......12, 12.5. But I have plenty of other drills if needed.

Quote:
What's the largest size of tonehole you are comfortable with?

Say 11mm? 10.5 better...

Quote:
How big a finger stretch can you accommodate between T2 and T3, and between B2 and B3?

Let's try 35mm between T2 & T3, and 37.5 between B2 and B3. Could push them a little more, but nice if not necessary. Those figures taken from an original Pratten. My Moon cylindrical pushes the B2-3 to 41mm but I find it a stretch.

Now, I'd normally aim for an oval embouchure hole of say 12mm long and 10.5mm across. To make it easier to repeat and calculate, if I use a 10mm bit and mill a slot 12mm long? So it will end up with the area of a 10mm circle, plus a rectangle of 2 x 10mm? No undercutting.


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PostPosted: Wed Jan 09, 2019 8:10 am 
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Terry McGee wrote:
Ah, a plastic folder cover that is 0.38? Also in orange!

So that 80-100mm counted from the top of the tube and so includes the stopper? And the embouchure hole goes through it? Might need to glue it around the embouchure hole to prevent it moving?
Sounds excellent. The colour coordination is particularly important.

The length is counted from the stopper face, and yes, the embouchure hole goes through it. We might be able to get away with an oversize gap in it for the embouchure hole, so there's no risk of it encroaching on the embouchure hole in the conduit. Determining the length and installing it will be the last step in the construction, so don't glue anything yet.

From here on, I'm going to ignore anything above the stopper face, since it is acoustically invisible. As long as you have enough conduit there to move the stopper up and down and remain secure, all is good.

Terry McGee wrote:
Now, I'd normally aim for an oval embouchure hole of say 12mm long and 10.5mm across. To make it easier to repeat and calculate, if I use a 10mm bit and mill a slot 12mm long? So it will end up with the area of a 10mm circle, plus a rectangle of 2 x 10mm? No undercutting.
Whatever works to give a reasonable approximation of your usual cut. Undercut as you think necessary for playability.

Tunborough wrote:
Let me know what range of pitches you can get with that tube. For example, by varying your breath, you might be able to play D4 varying between 281 - 291 Hz, D5 between 566 and 586 Hz, A5 between 855 and 880 Hz, D6 between 1150 and 1180 Hz, before the flute switches into the neighbouring register.
Correction to these instructions ... For each note, vary only your breath speed to determine the range of frequencies for that note. Going between notes (harmonics), you'll want and need to adjust your mouth to take a good run at the new note. I could ask for only one nominal playing frequency for each harmonic, but since there are so few notes at this stage, I'd like the two extremes for each one to get more data.


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PostPosted: Fri Jan 11, 2019 3:45 pm 
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Thanks for that Tunborough, sounds very doable. I hope to get to get on to that today.

Sorry to have gone quiet on this, I've been a bit tied up with big carillon developments and plumbing. Installing a fire pump and fire hose reels around the house and workshop. Climate change is making bushfires an increasing risk in this part of the world.

And you thought the Fire Hose Reel was the name of a tune?

I quipped to my plumbing mate that we're in the same line of business. Controlling the way transparent fluids pass up and down inside hollow vessels...


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