Rushing the Bore to Flatten Notes

[Ceann Cromtha]

I am curious as to why notes are lowered when we rush the bore of a chanter or regulator. I’m not disputing that this is exactly what happens, but it’s always seemed a bit counterintuitive to me (and not just me — a longtime piper, maker and “poster emeritus” on this forum once said unprompted that it was counterintuitive to him as well).

One reason it seems odd is that, shortly after the spectrographic analysis was invented in the 1950s, acoustic phoneticians discovered that sounds produced with the tongue raised in the mouth (thus reducing space inside it) have higher frequencies than those with the tongue lowered in the mouth (thus increasing space inside it). They explained this using the analogy of a water jug: a jug containing more liquid will produce a higher-pitched sound when struck or blown than one with less liquid. This makes perfect sense.

So, why is pitch lowered when we reduce the space inside the bore of a chanter or regulator? It seems like the activity in these conically-bored tubes is pretty much the same thing that’s going on in the “supralaryngeal vocal tract: at the base you have a vibrating element (reed/vocal cords a.k.a. vocal folds), a tube whose length determines fundamental frequency, etc. Can anyone explain why reducing space in one raises pitch while doing so in the other lowers it? Thanks!

[m4malious]

Is a direct comparison actually valid?
A rush in a bore would be acting on the freedom of the air molecules to move about, post the sound generation device (i.e. reed)
whereas changing the shape of the mouth (let's use oboe as example) is a change to the resonance chamber pre sound generation device (i.e. the reed).
E.g. a common advice on the oboe for (correcting) a sharp E is to "...open the oral cavity..."

M

[Ceann Cromtha]

Thanks, m4malious. I appreciate the possiblity that the comparison may not be valid — I was thinking that the most difficult one is that our vocal apparatus doesn’t have tone holes (but we change the shape and size of it by moving our mouths, things in the mouth, etc.

However, I may have confused you in another way. I’m not talking about a person playing something like an oboe; I’m only talking about that person talking, singing, etc. The sound generation device is at the same place in each — at the very bottom of the “tube”: in the human, it’s the vocal folds (cords) in the larynx (below that is the air supply/generator — the lungs) and in the chanter it’s the reed (and above that is the air/supply generator — the bag/bellows).

https://www.researchgate.net/figure/A-d ... _277131520

Also, what you say does indeed apply to both: the matter does inhibit the air molecules moving about. I’m wondering why in one it results in a lower pitch and why in the other does it result in a higher pitch.

[m4malious]

Thanks for the clarification.
It's an interesting question, but again I wonder if comparison is equal - complexity of the vocal resonance chamber combined
with almost infinite individual variations suggests to me that changes there would be more akin to adding chambering and additional
holes to a chanter bore, rather than just inserting a rush i.e. the "shape" of the "bore" is having more impact than just it's volume...
Also, are the changes in vocal shape actually altering the fundamental? Or is it that the complex harmonics in vocalisation are being altered
and that is what is giving the perception of pitch change?

As a test, if a singer produces a note constantly and an external "rush" is inserted into the mouth (the mind boggles), what is the impact on the pitch then?
For a related bit of fun, try this - https://dood.al/pinktrombone/

M

[Pogles]

Hi there, I’m new to playing (I have only been practicing the chanter for just over a year). This is my first and probably only post, as I prefer to stay in the background or to be a "lurker" as they say. But the puzzle piqued my interest. I have noticed that sometimes, back D lowers in pitch if I am applying too much pressure to the bag. But the intended pitch reestablishes itself when I ease off the pressure. My intuition is that when I squeeze the bag too forcefully, the pressure around the reed lips cannot decrease quickly enough, slowing the rate of vibration for longer, due to the fixed amount of space that the chanter offers for wind to escape and pressure to decrease. Perhaps a similar causal mechanism is at work in a rushed chanter? Viz, the rush increases pressure around the reed when the player tries to push the same amount of wind into the chanter at the same rate when compared to the same chanter but without a rush; presumably reducing the rate at which the pressure can decrease around the reed lips, leading to a lower heard pitch – temporarily in the case of someone with poor bag control like myself, or permanently and deliberately in the case of a rushed chanter or regulator? If this is along the right lines (I have no idea, it is only a guess), the water jug analogy may not be quite appropriate unless we treat overflow of liquid, or increased pressure inside the jug if we give it a fixed lid and pump more water into it than it is designed to hold, as the analogy to heard change in pitch of a rushed chanter. I'm not sure if any of this makes sense

Nick

[geoff wooff]

The 'rushing' of a regulator will lower the notes because it makes the bore smaller , in diameter or volume. If one compares the small parallel bore of a Northumbrian Small pipe chanter where a much lower note can be achieved at the same length as a UP regulator due to the reduced diameter. Yes I know the physicists will argue that a parallel bore has a different regime but the effect is similar.

Narrowing the angle of taper in a conical bore will lower the pitch of the note issuing from the open end or a side vent hole In this way the conical bore can be designed to play a desired scale at comfortable finger spacings.

[Ian Lawther]

Yes I know the physicists will argue that a parallel bore has a different regime but the effect is similar.

Years ago at a folk club in London I saw Liam O'Flynn having trouble tuning his bass drone. Eventually he removed the end and put something inside and then proceeded to finish tuning. Later I asked him what he had done and explained the drone was tuning too far out on the tenon so he had put a thin piece of cane inside the tuning slide which effectively dropped the pitch of the drone allowing him to tune higher on the tenon. Effectively he was rushing a parallel bore.

[MichaelLoos]

A few things got mixed up there.
First, the oboe player changing the internal volume of his oral cavity can not at all be compared to rushing the bore - the equivalent to the oral cavity would be the wind chamber (chanter cap), as m4malious has already pointed out. Changing the chanter cap can indeed have a great effect on both pitch and tuning of the scale, but that's a different story.
Next, the comparison with the water jug is not valid, the water jug is a Helmholtz resonator which is an entirely different beast than a musical pipe.
The pitch of a pipe is in the first place, but not only, determined by its length, other factors are the bore diameter and also the internal volume. If you leave the length unchanged but reduce the diameter of the bore, you are basically shifting the ratio of length : width in favour of the length, while the absolute length is the same, the relative length has increased. Another way to visualize this is that by the smaller diameter the sound wave is being flattened, with the effect of the tone lowering. Also, the rush being an obstacle, causes the air flow to slow down.
Mind you, this is not totally physically correct - what happens in fact is a lot more complicated, but it serves to work with it.
A way to increase the internal volume while leaving bore length and width (mostly) unaffected is - drilling finger holes and covering them. The chimneys of the holes do increase the internal volume, and as any pipemaker will confirm, the adding of the finger holes does lower the pitch of the pipe. This can be explained by the greater volume and also by perturbations caused by the edges of the holes - that's why undercutting a hole can sharpen the note significantly, you're removing the obstacle which slows down the air flow.
As a matter of fact, the only textbook available for wind instrument makers (in Germany 20 years ago) had this wrong - years ago I had a conversation with an oboe maker who was absolutely convinced that a wider bore must lower the pitch because of the increased internal volume - while it does sound plausible it is not the case. I asked him "did you ever try what happens if you widen the bore?" and he replied "I would never mess around with that, I'm glad enough that it sort-of works the way it is!"

[Ceann Cromtha]

Thank you all for your detailed and thoughtful responses. There's a lot to digest and consider here.

[ennischanter]

Yes I know the physicists will argue that a parallel bore has a different regime but the effect is similar.

Years ago at a folk club in London I saw Liam O'Flynn having trouble tuning his bass drone. Eventually he removed the end and put something inside and then proceeded to finish tuning. Later I asked him what he had done and explained the drone was tuning too far out on the tenon so he had put a thin piece of cane inside the tuning slide which effectively dropped the pitch of the drone allowing him to tune higher on the tenon. Effectively he was rushing a parallel bore.

Fascinating, I love anecdotes like these, thanks for sharing.