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Old 07-12-2020, 03:27 PM   #1
Jon Snow
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Default "Phase locking" drones

I made a short video showing "phase locking" of drones using adjustable length drone stocks. I'd be interested in any comments or feedback.


https://youtu.be/PHvs4XAd1wg
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Old 07-12-2020, 05:33 PM   #2
Steven Knox
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Default Re: "Phase locking" drones

Very good demonstration. Thanks for posting this.
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Old 07-12-2020, 11:20 PM   #3
William McKenzie
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Default Re: "Phase locking" drones

Jon thanks for posting this!

Can you explain a bit more about them, so the stock itself is able to be lengthened or shortened which allows (bag side of) the drone reed to "phase lock" with the other reeds within the bag?
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Old 07-13-2020, 05:06 AM   #4
Jay Close
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Default Re: "Phase locking" drones

I think this is very intriguing. My questions are what harmonic the stocks are tuned to, why that one and how is that accomplished? I was friendly with the late Dr. John Kidd who also researched phase locking, but the result shown on mr. Snow's video is much more dramatic than any I experience the two times I played a Kidd bagpipe.
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Old 07-13-2020, 08:15 AM   #5
Jon Snow
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Default Re: "Phase locking" drones

Quote:
Originally Posted by William McKenzie View Post
Can you explain a bit more about them, so the stock itself is able to be lengthened or shortened which allows (bag side of) the drone reed to "phase lock" with the other reeds within the bag?

I will explain what I believe is happening, although I freely admit there are some speculations and assumptions here.


The basic idea is that the reeds are interacting with each other.



When a reed vibrates (call it reed A), it creates puffs of air that exit the drone and are perceived by our ears as sound. These puffs of air also reach the other reed (reed B), which is also vibrating, and will tend to encourage reed B to vibrate at the same frequency. If the two reeds do in fact vibrate at the same frequency, "locking" occurs.


Obviously many things could prevent locking. Reed B has it's own frequency of vibration happening, governed by the length of its own air column. Reed B's tongue might be too stiff to be affected by Reed A's puffs of air. Or Reed A's puffs of air might be just too weak by the time the get to Reed B to have any effect.


One of the things we can do to increase the probability of locking is to look for ways to make Reed A's puffs of air stronger when they arrive at Reed B. Note that the interaction between Reed A and Reed B happens inside the bag, where the reeds are only a few inches apart (sound energy decreases as the square of distance). Stronger puffs of air equals louder sound, so we need to make the reed sound louder inside the bag.


If we think of the stock as an air column in its own right (which we usually don't, but it is an air column), it has its own resonant frequency. The stock will tend to pass or even amplify frequencies that match its own resonances, while attenuating those that don't. Thinking of the stock this way, it makes sense that adjusting the length would have the potential to increase the volume of sound inside the bag and increase the potential for locking drones.


The actual process of lengthening the stocks and figuring out the best position was largely trial and error, although I did put a microphone in the bag and ran a spectral analysis program on a laptop to see what was happening inside the bag when I changed the length of the stocks. It turns out that the 2nd harmonic of the drone (720 Hz) is the most prominent inside the bag, and jumped up dramatically as I reached the stock length that I am now using. I would also note that the air column length inside my stocks is very close to the length that would be predicted for a tube with a fundamental frequency of 1440 Hz, which is the 5th harmonic of the drone (and double the 2nd harmonic frequency).


This is probably a lot more than you were looking for, but I've had a lot of thoughts about this rattling around so it's probably a good thing for me to write them down and organize them.
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Old 07-13-2020, 09:00 AM   #6
EquusRacer
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Default Re: "Phase locking" drones

My head just exploded!

Clearly, much of this is beyond me; yet, in my ignorance, I do have a question regarding variables. What, if any, effect is there with different types of bags, including materials (e.g., leather vs. synthetic), size, positioning of drone stocks, etc.
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Old 07-13-2020, 09:31 AM   #7
Michael Flemming
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Default Re: "Phase locking" drones

How different is the length you’ve arrived at from the original Gibson stock?
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Old 07-13-2020, 09:40 AM   #8
Jon Snow
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Default Re: "Phase locking" drones

Quote:
Originally Posted by Michael Flemming View Post
How different is the length you’ve arrived at from the original Gibson stock?

1/4 inch or so longer. I don't have a final number yet. I'm working on a non-adjustable set of stocks and expecting to have to tweak them a bit.
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Old 07-13-2020, 10:09 AM   #9
Patrick McLaurin
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Default Re: "Phase locking" drones

So if one was lucky, they could just not have their drone bottom shoved all the way into the stock.

Really cool demonstration. Interesting how the harmonics change as you move through the locked region.

Does it persist with the bass and/or chanter going or do they overwhelm the communication?
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Old 07-13-2020, 01:20 PM   #10
Kevin
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Default Re: "Phase locking" drones

This is interesting. Are you finding that the optimum stock length depends on reed strength or type, or is it only a function of the fundamental frequency of the drone note?

If it is the latter, and doesn't need to be adjusted too often, I am wondering if you could do it from inside the (zippered) bag by sleeving each stock with thin brass tubing that can be pushed in or out to change the stock length.

Best regards,
Kevin

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