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Old 07-26-2020, 11:15 PM   #41
Achilles Piper
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Default Re: "Phase locking" drones

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Originally Posted by Jon Snow View Post
Not to be to argumentative, but what is your source for this? Definitions of "harmonic" that I am finding with a casual internet search, for example here, indicate that the term applies to whole number multiples of the fundamental, but not the fundamental itself.
By all means delete reference to "1st harmonic" if you like, as long as we agree that the 2nd harmonic is at 2x fundamental, 3rd harmonic 3x etc. It is not possible to have a 2nd harmonic at 720 Hz and a 5th harmonic at 1440 Hz - they are actually 3rd and 6th harmonics.

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I would love to see where this has been demonstrated? I have never found any reasonable description of what is happening acoustically inside a bagpipe drone.
Some years ago, a contributor to this forum, bob864 I think it was, published several spectra of bagpipe drones on the forum. Others have done the same. The result each time is to show that all harmonics up to at least the 12th are present. Sorry, I can't find the threads.

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In any event, with apologies for imperial measurements, my tenor drone is 18-5/8 in. long. This includes the reed (up to the reed plug), but not the stock, obviously. Using the speed of sound as 13504 in./second, an open pipe would result in a fundamental frequency C/2L = 363 Hz. A closed pipe would be C/4L = 181 Hz. Neither are anywhere close to the actual fundamental of around 240 Hz.
I ventured that a drone is a closed pipe because the reed acts as a stopper: that end of the pipe is definitely closed. If it was a simple closed pipe we should get a fundamental corresponding to a quarter wavelength and only odd harmonics. Changes in the bore diameter, the presence of the tuning chamber, bell and drone top all make the accoustical situation more complex. I've not seen any analysis of an actual drone. Isn't our instrument wonderful?
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Old 07-27-2020, 06:52 AM   #42
Jon Snow
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Default Re: "Phase locking" drones

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Originally Posted by Achilles Piper View Post
I ventured that a drone is a closed pipe because the reed acts as a stopper: that end of the pipe is definitely closed. If it was a simple closed pipe we should get a fundamental corresponding to a quarter wavelength and only odd harmonics.
I guess my point was that it's unclear to me how the drone produces the frequencies it produces. Despite it's apparent physical configuration, the tenor drone produces all the harmonics of the fundamental, and therefore clearly behaves as if it were an open pipe, but with a length of around 50% longer than its actual length (100% for the bass drone).
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Old 07-27-2020, 11:59 AM   #43
Patrick McLaurin
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Default Re: "Phase locking" drones

For those reading along, some plots of a tenor drone frequency spectrum can be found in this blog post:

https://www.patrickmclaurin.com/wordpress/?p=458
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Old 07-27-2020, 12:50 PM   #44
Kevin
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Default Re: "Phase locking" drones

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Originally Posted by Jon Snow View Post
I guess my point was that it's unclear to me how the drone produces the frequencies it produces. Despite it's apparent physical configuration, the tenor drone produces all the harmonics of the fundamental, and therefore clearly behaves as if it were an open pipe, but with a length of around 50% longer than its actual length (100% for the bass drone).
It seems that the drone is most like a closed conical bore air column that plays a fundamental an octave lower than expected (for a conical bore). Definitely seems like an odd combination of characteristics....

Kevin

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Old 07-30-2020, 02:35 PM   #45
Jon Snow
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Default Re: "Phase locking" drones

I've now made some non-adjustable stocks that are tuned for locking. I have them tied into my pipes and they lock nicely. Drawing is attached.

These ended up being about 3/8 in. longer than my adjustable ones were, which I did not expect and cannot explain. I can only suppose that the fact that the brass sleeve did not extend the full length of the adjustable stock must have something to do with it.

I'm interested in getting a few sets of these into other people's hands to get some feedback. I would have to charge for them; I'm thinking $40 US plus shipping per set will cover my materials and a beer or two while I'm working. If anyone in the is interested in this please let me know in the comments or send a PM. If there's some interest I'll order the materials contact you individually later to get your drone tenon measurements.

Link to new drawing.
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