drone lengths - what do you use?

Pipemaking, reedmaking & maintanence. Expert pipemakers are eager to answer your questions

Re: drone lengths - what do you use?

Postby Dave S » Sat Sep 24, 2011 8:48 am

Tim Rolls wrote:Hi Mike,

What I'm interested to know is what the critical elements are here. Is the length of free tongue the pitch determining factor, so on the metal reeds, to the end of the tongue, and on the cane reeds from the cotton binding to the cut in the cane, or is that inconsequential in comparison to the length from the end of the reed to the hole at the top of the drone, or a combination of the two. Is it important, as with the chanter, exactly how far in the reed sits in the drone body, or does the tuneable nature of the drone mean this isn't crucial? Or should I just go and read everyone's books then come back again with all the new questions that will raise?

Tim


Hi Tim

Up to now no-one seems to have mentioned volume, an oversight that I believe is important. If the volume that the reed is trying to feed offers too much or to little "impedance" it will not be reliable, or just not be "happy"
I once thought about getting a Lachenal practise squeeze box moved up about 25 hz, the expert told me that it could be done but it would involve modding all the reeds and the chamber sizes to make a reasonable job of it. The cost was more than a set of pipes so I got the pipes --- free reeds involve matching volumes apparently, but check it out with an expert.
I know some drone stocks cover the reeds and some don't, and the bores of the standing piece can vary by 0.5mm which makes a great deal of difference to the volume the reed is trying to feed. Try the following, get a macdonalds straw, cut it along its length then cut a section off along its length, just enough to form a tube inside the bore of a small drone. Then insert this volume reducer into the small drone standing tube and note the difference it makes.
It also reduces the air flow through to drone --------

Dave
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Re: drone lengths - what do you use?

Postby Barry Say » Sat Sep 24, 2011 10:57 pm

Responding to Tim: (in perhaps a roundabout and verbose fashion)

We know that it is perfectly possible to make chanters in tune. I have carried out calculations which show that chanters made to the Colin Ross/Mike Nelson specification in Mike's original pipemaking book will be in tune. Mike's published hole spacings can be shown to be almost identical to the spacings I received from Colin at the Killingworth pipemaking classes.

The chanter is driven by a very sensitive double reed. It is very responsive to pressure variations and this is important to allow the player expression.

The drones have single beating reeds. The idea is that these should less sensitive to pressure, so that the player can minutely adjust the bag pressure to adjust the intonation (tuning) of the chanter, without shifting the pitch of the drones.

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WARNING - some readers may find some of what follows unintelligible - SORRY
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In scientific/mathematical terms I think I have just described the difference between a linear system (the chanter) and a non-linear system (the drones). A linear system can always be described by a set of straight line graphs, although it might take an awful lot of maths, sums, coffee and twinkie bars to get there. A non-linear system can never be fully described by straight lines. One one the major ways that we coped with non-linear systems (in my profession) was to understand that in fairly restricted circumstances, they appeared to behave in a linear fashion.

So, in terms of drones,
  • as we lengthen the drone, the note flattens. We could call this a trombone effect (or Swanee Whistle - depending on your cultural background)
  • Shortening the drone has the converse effect.
We also have rules which allow us to adjust the reed.
  • Moving the bridle or changing the wrapping to change the length of the blade
    • Longer blade - lower pitch
    • Shorter blade - higher pich
  • Adding weight
    • Adding weight at the tip flattens the note
    • Removing weight from the tip will sharpen the note
  • Scraping
    • Thinning the reed near the bridle (wrapping) flattens the drone
    • Scraping is irreversible
  • Set - The set of the reed describes the separation of the reed blade from the body'
    • Large set- Flat - loud - hard to start - plays at high pressure.
    • Small set - Sharp -quiet - easy to start - shuts off at high pressure.

All of the above are linear adjustments, but if you change things too much, you will get into an area where things go crazy.

Sorry folks, at this point my knowledge runs out. This is the place where experience comes in. If I could explain what I have come to know about reeds (which is 3/10's of knob-all). I would tell the world, in the hope that pipers would be able to keep their pipes in order, to their satisfaction, without the need to consult or pay a pipemaker or fettler.
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Re: drone lengths - what do you use?

Postby John Gibbons » Thu Sep 29, 2011 2:11 pm

Tim Rolls wrote: What I'm interested to know is what the critical elements are here. Is the length of free tongue the pitch determining factor, so on the metal reeds, to the end of the tongue, and on the cane reeds from the cotton binding to the cut in the cane, or is that inconsequential in comparison to the length from the end of the reed to the hole at the top of the drone, or a combination of the two. Is it important, as with the chanter, exactly how far in the reed sits in the drone body, or does the tuneable nature of the drone mean this isn't crucial? Or should I just go and read everyone's books then come back again with all the new questions that will raise?


Length of free tongue is important - think of a ruler being pinged against a desk. This is thinner and shorter, so higher frequency, but the longer the free tongue the lower the pitch. This is why moving the bridle a mm or so acts (inter alia) as a coarse adjustment of the pitch. But the tongue, by itself, is a horribly nonlinear damped, driven oscillator, and doesn't go at a definite frequency. So it is hooked up to a linear resonator, the air column in the tube of the drone. The length of tube between the reed tongue and the open hole determine the resonant frequency - this needs to match a frequency the reed can actually vibrate at. If they don't roughly match you get squeaks, double toning and all sorts of pathology.
The whole reed-drone system is highly complex, and not properly analysed theoretically, so copying good existing models is a very good place to start. The rules of thumb which Barry quotes then let you converge on a drone which not only speaks, but is even tunable, and stable under pressure changes.

John
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