Bore roughness and tone

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Conical bore
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Re: Bore roughness and tone

Post by Conical bore »

david_h wrote: Thu Jul 01, 2021 3:28 amI get the impression that no-one in this discussion has serious disagreements with Geoffrey Ellis' observations given in the third post of the thread. Smoother bores give a 'brighter' sound.
I'm not so sure about that. The smoothest surface you can get in a wooden flute's headjoint is with a full brass metal liner like my Aebi, but I can't say the tone is brighter than the unlined Windward flute I played before it. The tone isn't exactly the same as the Windward but I don't hear a noticeably brighter tone in the sense of high frequency harmonics or a sharper edge. Both flutes "sound like me" with some minor volume difference, the Windward being a hair louder as you'd expect with a Pratten-ish design vs. the Aebi Rudall copy.

Maybe it's because most of the sound is coming from the vibrating air column in the rest of the bore, and the headjoint is just an "exciter" to get the column vibrating, so the metal liner doesn't contribute anything? I would still think the difference in surface smoothness would have *some* impact if smoother is always better, or always brighter.

Anyway, I keep coming back to the idea of a threshold of smoothness that's good enough, like bare wood with a thin film of moisture after playing, and you wouldn't hear the difference if the bore was even smoother on the microscopic level. Otherwise everyone would be playing glass and metal flutes. Or at least preferring fully metal-lined headjoints in a wooden flute, which doesn't seem to be the general preference among modern "Irish flute" makers.
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Re: Bore roughness and tone

Post by Geoffrey Ellis »

Terry McGee wrote: Thu Jul 01, 2021 7:38 am But consider the potential risks to the flute in general. Imagine it's a keyed flute, and the spinning rod jams and whips the section of flute out of your hand and starts it flailing around, slamming into bits of furniture. Within a few seconds, you've reduced your left-hand section to a cluster of bent silverware and cracked blocks. Nasty.
This made me chuckle. I polish the bores of my flutes with the fine steel wool wrapped around thin metal rods that are chucked in a drill, and I can't count the number of times something unexpected happened and the spinning rod "grabbed" the flute out of my hand (sometime providing some nice friction burns to my hand in the process). Luckily I don't make keyed flutes! The other thing to be careful of with this approach is having too much of the steel wool on the rod and trying to polish a bore whose diameter constricts. You can get your rod jammed in the bore and getting it out is no joke. That's a whole other discussion...

I find the scientific approach to this topic of interest, intellectually, but as it has gone on I've sort of wondered what would be the point of refining some of these experiments, beyond the simple joy of understanding why something works the way it does (though I'm skeptical of arriving there, personally :-) ). In the "real world" of flute playing and making, the issue of bore smoothness, how to achieve it, what effect it has on tone and playability, etc. seems relatively obvious. Going way back, woodwind makers have sought fine-grained timber and naturally oily woods for flutes, and they have taken pains to oil and polish the bores because everything works better when they do. Inner bore surface has an impact on a flute's tone and response (sometimes dramatic if one is transforming really poor timbers using things like epoxy), but I personally doubt that any amount of micro-analysis, measuring of impedance or other such controlled tests are going to yield anything more profound than that which has already been discovered by generations of makers using simple trial and error and observation. And separating the effects of bore smoothness from a host of other factors such as bore shape and volume, embouchure cut, wall thickness, hole size, player technique, as well as the sometimes controversial question of "materials" (blackwood versus boxwood, or mopane versus maple--questions that are also tangled with this current question of the inner surface) is a puzzle that might not have a solution :boggle: .
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Re: Bore roughness and tone

Post by Geoffrey Ellis »

Conical bore wrote: Thu Jul 01, 2021 8:05 am Anyway, I keep coming back to the idea of a threshold of smoothness that's good enough, like bare wood with a thin film of moisture after playing, and you wouldn't hear the difference if the bore was even smoother on the microscopic level. Otherwise everyone would be playing glass and metal flutes. Or at least preferring fully metal-lined headjoints in a wooden flute, which doesn't seem to be the general preference among modern "Irish flute" makers.
I think this is it in a nutshell. I think once you get to a certain level of smoothness, you might get some perceptible changes in timbre, from darker to brighter, but you can really only sort that out if you are playing two truly identical flutes, which (to my knowledge) don't exist.
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Re: Bore roughness and tone

Post by david_h »

Terry McGee wrote: Thu Jul 01, 2021 7:38 amSo, be careful. Don't undertake anything you are not confident you can control.
Thanks Terry. I am wondering if I have something fast but low powered that will stall before any damage is done. Another option is a large, old, manual hand drill fixed to the bench. That may be best with that aid of an assistant.
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Re: Bore roughness and tone

Post by skap »

Geoffrey Ellis wrote: Thu Jul 01, 2021 8:26 am And separating the effects of bore smoothness from a host of other factors such as bore shape and volume, embouchure cut, wall thickness, hole size, player technique, as well as the sometimes controversial question of "materials" (blackwood versus boxwood, or mopane versus maple--questions that are also tangled with this current question of the inner surface) is a puzzle that might not have a solution :boggle: .
Well, actually among all those effects, the effect of bore smoothness is the most easily separable one, no?
Plus it should be converging, that is infinitesimal change in bore smoothness will produce infinitesimal
change in tone, response, whatever, and I feel that we all agree on this one now, although it was not clear
at the beginning. I think, the real question is how does it rate with respect to other effects. This is why
I asked if boxwood could be polished as smooth as blackwood. If you admit that it is not the material, but only
the geometry of its surface that matters, that really messes everything up. Just think about condensation,
while it "smooths out" a rough bore, it makes a smooth bore rough (micro droplets everywhere and they are
growing as you continue to play, horror!), practically immediately as you start to play, so you can never really
play a really smooth bore in a real world. Instruments in synthetic materials have a tone quite different
from the wooden ones, is it because their smoothness is just a little bit different (microscopically!), or is it
because their elastic properties are TOTALLY different (hmm, sound waves are sometimes called elastic waves,
especially when travelling in solids, there must be some connection here): which one is more likely ?

Perception of sound is not purely mechanical, psychology is involved, and our brain has an effect on what
we here. If the real physical change is too subtle to be detected but our brain knows that there must be a
change it will just made it up according to it bias, it's just how it works, and it will feel totally real.
But no one is unbiased, my bias is just the opposite: I don't believe in it and thus I don't hear the
difference even if it is there. That's why I'm not going to attempt to make the bore of MY flute any smoother.
My point is that an effect should be significant enough so you can hear it against you bias, only then you
can be sure it's real. I came to disliking flutes from synthetic materials against my bias (being initially
very attracted to the idea), that's why I think its real. Is it the case with the bore smoothness ?
Provided, of course, you keep it in reasonable limits.
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Re: Bore roughness and tone

Post by Geoffrey Ellis »

, actually among all those effects, the effect of bore smoothness is the most easily separable one, no?
Maybe this is true if you can can get all of the other factors as close as possible on two test flutes. I think that comparing two different flutes from two different makers (for example) would make a comparison of bore smoothness less helpful (or pointless) because other small design changes can have a big effect on how the flute plays and sounds. But if a consistent maker made two flutes from the same material and made them as close to identical as possible, then a meaningful test with bore smoothness would be possible. This is how I arrived at my own convictions on the subject, because I've done some form of this comparison many, many times.

I wrote a blog at one point called The Materials Argument (https://www.ellisflutes.com/blog/the-materials-argument) where I went into the subject in some depth, particularly as regards bias. Confirmation bias renders many comparisons less useful, and the perennial question of what material to use for a flute is hopelessly subjective. I think it usually takes a really dramatic difference to overcome that bias, as you have indicated. The use of high-quality microphones and high-fidelity recordings can help separate what is more objectively audible from what is more subjectively experienced by the player, I think. But I question the value of that as well, depending upon what one is trying to prove with comparisons. I don't think most players are primarily concerned with what the audience hears, placing more importance on what they hear and feel as the player of the instrument.
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Re: Bore roughness and tone

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Off topic slightly, but prompted by reading Geoffrey's blog article about materials and related to player perception. Are we sure that when we feel the flute vibrating in our hands that the material is actually resonating? Could we be feeling the reaction of it pushing out a positive pressure pulse at one end followed half the frequency later of it pushing one out the other end. The flute moving bodily around as it does its stuff transmitting energy into the air. If so then for the same volume of sound a lighter flute would be moving more simply because it was lighter, not because of any other properties of the wood or energy transmission at the internal walls. Or does the flute site passively in our hands as the standing wave does it's stuff?
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Re: Bore roughness and tone

Post by Terry McGee »

I'm not convinced we can feel vibrations in the bodies of our heavy-timber flutes, but I haven't tried to prove or disprove it. (Broad hint to next generation!). My feeling it's more likely that we are directly sensing the vibrating air column through direct contact via the finger holes. Having said that though, I did try one little experiment that might lead to the opposite conclusion. I took my Snark guitar tuner (set to vibration sensing mode, not microphone), clipped it onto a key on my keyed flute and played a scale. The tuner had no trouble following the action, which seems to suggest it was successfully sensing vibration. But was it vibration of the flute body or perhaps of the key reacting to the vibrating air column? One really needs to attach a vibration sensor with metering to various parts of the flute body itself before drawing too many conclusions.

I believe I can detect vibration in the body of my Pine Prattens. This abomination was a reductio ad absurdum exercise to explore the question of the significance of materials in flute making, and proved what we could expect it would prove. If you pick a material stupid enough, it won't make a good flute. Pinus Radiata has a density around 0.4, compared to Walnut at around 0.7, Boxwood at around 1.0, Blackwood around 1.2 and Delrin around 1.4 times the weight of water. It's my feeling that nothing under a density of around 1.0 is worth toying with (unless successfully "bulked up" by impregnation).

Here's an image of this fine instrument!

Image

And you can read the article at: http://www.mcgee-flutes.com/pine_prattens.htm

If one can sense or otherwise detect vibration of the flute body (as opposed to the vibration of the air column within), one has to accept immediately that the energy one is feeling is energy that is wasted - i.e. not being converted into sound.

Now, speaking of Delrin (I mentioned its density above) I don't remember us including it in our discussions so far (I may be wrong!) It surely is relevant to this topic. A number of us make flutes in Delrin and also in the fine flute timbers. Delrin is a bit more dense and is capable of a smoother finish and so we might expect it to have a stronger response. I don't think I'd argue that, but I haven't submitted it to analysis. If we assume the performance is proportional to the density, then we might expect a 1.3dB (deciBel) increase over Blackwood. Probably not noticeable. 1dB is the JND (Just Noticeable Difference) for an immediate change in a constant tone as detected by a musical ear. Putting down one flute and lifting another probably violates "immediate". 3dB is the JND for normal listeners and normal program material. We'd lie somewhere between.

Or a 10dB increase over Pinus Radiata. I.E. one Bel. By definition, about a doubling in loudness. Oooh, that's credible!
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Re: Bore roughness and tone

Post by david_h »

Terry McGee wrote: Sun Jul 04, 2021 7:13 am If one can sense or otherwise detect vibration of the flute body (as opposed to the vibration of the air column within), one has to accept immediately that the energy one is feeling is energy that is wasted - i.e. not being converted into sound.
That's the part I was wondering about. "Every Action has an Equal and Opposite Reaction", Newton's Third Law. Can we make the air shake without shaking ourselves? If someone is filling the room with sound, moving peoples eardrums, rattling the windows etc they are projecting energy into the room. Is their a 'recoil' ? If so for the same momentum a lighter flute would have to move further. Does a player get more feedback from a boxwood flute than a Delrin one?
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Re: Bore roughness and tone

Post by Terry McGee »

I'm thinking that any recoil is going to be very small, due to the very great ratio of the weight of the flute compared to the weight of the air inside it. I guess we could calculate that? (Gulp!) Assuming an average bore diameter of 15mm and a length of around 600mm, I'm getting 0.13gms. (Somebody check me!) (The ISA or International Standard Atmosphere states the density of air is 1.225 kg/m3 at sea level and 15 degrees C.)

One of my keyless flutes weighs around 300gms, so that would reduce the recoil (when compared with the air movement) by about 2300 times. The Pine Prattens comes in just over 100gms, and would still reduce the recoil by 770 times.
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Re: Bore roughness and tone

Post by david_h »

You are not just shaking air in the flute. You are shaking all the air in the room, and the neighbouring room if the walls are thin enough. Though even in the flute you are not moving all of the 0.13gms, just sending a ripple through it every cycle.
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Re: Bore roughness and tone

Post by Terry McGee »

Yeah, it's extraordinary how much air we can shake (how much sound we can make) from an instrument with (apparently) no moving parts. We do of course have moving parts, they are the air molecules we direct towards the edge, and whose meagre energy is wonderfully amplified by the magic of the jet-switching mechanism. I'm not convinced though that we are likely to incur much recoil effect, but am open to the notion being proved.

It's probably good at this stage to assemble a list of possible side effects that could make the vibrating air column tactile. I'll make a start:
- the energy in the vibrating air column directly sensible to the fingers through the finger holes
- vibration in the body of the instrument detected by the fingers
- recoil of the instrument body due to reaction against the projection of energy at the ends, detected by the fingers
- what have I forgotten?

Perhaps those who feel they can perceive vibrations in their instruments can chime in here with their observations? Do any of the above possible explanations attract you?
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Re: Bore roughness and tone

Post by david_h »

Is it just the vibrating air column? The jet-switching is where the energy is fed in and the perception was reported above that that end that is where most of the sound comes from.

As an aside, or rather closer the to topic :D , I just noticed that the unsw acoustics pages say clearly early on " Once the air in the flute is vibrating, some of the energy is radiated as sound out of the end and any open holes. A much greater amount of energy is lost as a sort of friction (viscous loss) with the wall." https://newt.phys.unsw.edu.au/jw/fluteacoustics.html
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Re: Bore roughness and tone

Post by Terry McGee »

david_h wrote: Mon Jul 05, 2021 9:18 am Is it just the vibrating air column? The jet-switching is where the energy is fed in and the perception was reported above that that end that is where most of the sound comes from.
Most of the sound emanates from the embouchure end, but it is the resonance of the vibrating air column that controls the jet-switching action. So if the efficiency of the vibrating air column is reduced (eg by a roughened bore), it will reduce the efficiency of the jet switching, reducing output even at the embouchure end.
As an aside, or rather closer the to topic :D , I just noticed that the unsw acoustics pages say clearly early on " Once the air in the flute is vibrating, some of the energy is radiated as sound out of the end and any open holes. A much greater amount of energy is lost as a sort of friction (viscous loss) with the wall." https://newt.phys.unsw.edu.au/jw/fluteacoustics.html
If the friction with the wall takes out "a much greater amount of energy" that that which is radiated, it seems to support the notion that a rough bore will take out more.

It would be nice to be able to compare spectra of a flute with a roughened bore and then the same flute when repolished. Problem is that you can only do that once, and that makes the measurement very dependent upon the player's embouchure on the day! My memory suggests that roughened bore flutes are also dull flutes, and that well-polished bores yield a brighter tone. That would seem consistent with our experience of metal-lined heads and Delrin flutes. I'm quite happy with the tone produced by a well polished wooden bore.
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Re: Bore roughness and tone

Post by Tunborough »

david_h wrote: Mon Jul 05, 2021 9:18 am" Once the air in the flute is vibrating, some of the energy is radiated as sound out of the end and any open holes. A much greater amount of energy is lost as a sort of friction (viscous loss) with the wall." https://newt.phys.unsw.edu.au/jw/fluteacoustics.html
I suppose they should know, but I'm not convinced about the "much greater" part. If you have chosen a suitable bore diameter, I had thought that at the bottom end of the range, energy loss due to radiation would dominate the wall losses, while wall losses would dominate radiation losses at the top of the range.

Certainly, at the lowest note, if the bore is too large, radiation losses dominate wall losses, while if the bore is too small, wall losses dominate radiation losses.
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