A while ago we once again discussed phase locking in drones. Here are two videos to help illustrate the phenomenon:
http://io9.com/5947112/watch-32-discordant-metronomes-achieve-synchrony-in-a-matter-of-minutes
http://www.youtube.com/watch?v=ADGmBtLJ6y4
Draw your own conclusions about how to couple and how strongly coupled various stocks and bag arrangements can be achieved.
Bob
Good one Bob, I think that pretty much shows that phase locking of drone reeds in a stock does not happen.
RORY
If not tongue in cheek 
, please describe the path between the videos and your conclusion.
I have to say I’m not convinced. The table has been forced to resonate and interacts with the metronomes, they eventually establish a ‘regime of oscillation’. I suspect that in a stock the air isn’t resonating, its natural frequency being very high. On the other side of the reed blade is the bore where the pressure is oscillating substantially.
My scepticism is really down to having tried to improve smallpipe drone stability by hollowing out the drone stocks. The only effect seems to be on tone and is down to the wall thickness being reduced. If you damp the stock with your hand both sound the same.
Sean
Yes I will, but can I ask you something first. Do you think the video’s, reinforce the theory of phase locking of drone reeds and if so why ?
RORY
What might be more interesting, from our point of view would be three ,or more, métronomes set to octave spacings like our drones . Place them on the free floating base and see what happens then.
One could also see that if three drone reeds were aligned and they locked in phase the vibrations could make the piper vomit ,like having sea sickness… that would be a waste of an expensive Pint. Still that thought relies on sound waves traveling in straight lines like Light..
Or you could take three pipers, with three Pints each, and watch them get locked.
Geoff, I am fairly confident that with three metronomes set to simple harmonic multiples and coupled in the same manner as the videos, that phase locking will occur.
Sound waves will transfer energy after reflection. . .tho’ I think your expensive pint is safe. . .
Rory, the question being begged is : Are drone reeds effectively coupled? Even weakly coupled oscillators will eventually phase lock. This is shown by the ‘hanging two pendulae on a common wall’ demonstration.
There is some confusion between resonance and coupling.
If the drone reeds share a strongly resonant space they will perforce attempt to phase lock and fairly quickly. The resonance will cause the strong coupling.
If the drone reeds share any common space, even the short channels in a solid stock, can they effectively be coupled?
Bob
Interesting video.
The phasing of the metronomes has nothing got to do with reflected waves ,it is caused by Newtons third law of motion (for every action there is a opposite and equal reaction) . As the arms swing one way the floating base moves the other way. The metronomes first influence the base and then the base influences the arms of the metronomes and brings them into synchronisation .
RORY
Rory the ‘Third Law of Motion’ is an excellent description of the energy coupling displayed in the metronome videos. (As opposed to thishttp://www.youtube.com/watch?v=hstPHM3R1dY).
The transfer of the energy is necessary for the phase locking to take place. Phase locking is an expression of entropy.
The question remains: under what circumstances can sufficient energy be transferred from one drone reed to another to cause phase locking?
The pulses of each opening and closing of the drone reed tongue creates the mechanical excitation of the sound column of the drone bore.
The bore in turn acts as a resonant cavity to reinforce and amplify the desired frequency (and possibly desired harmonics). It can be said that our desired sound outcome is the result of a close coupling of the resonance of the drone bore and the periodicity of the drone tongue. We all know without this ‘coupling’ the drone does not perform.
Do the “upstream” pressure pulses of the drone reed contain enough energy to influence the phase of another reed? If so, under what circumstances?
Bob
You do realize that sound is a mechanical phenomenon, right? 
What you’re describing there is frequency difference-beating between two independent oscillators (i.e. strings), one of which is being driven through different pitches. Phase plays a role in what you hear, but that’s a very different thing from resonant phase locking/coupling. Phase and pitch are independent. Harmonics have little to do with it; it’s mostly the fundamentals which contribute to the perceived beats.
No, when two strings are in tune to the same pitch they are not necessarily in phase. In fact, when plucked separately they’re are almost guaranteed not to be in phase. You’ll hear any phase differences as amplitude (loudness), not beats. Perceived phase is also a function of distance from the strings. And in theory, there are locations in space with 180 degree phase cancellation where you’ll hear - nothing. Which is a neat illustration of the independence of phase and frequency.
Of course, resonant (sympathetic) string coupling is certainly possible. But that’s not what you were describing.
why/how are you quoting content from my post that I had deleted 15 mins or more prior to your reply 
At the risk of putting everyone asleep, I have to ask “Why do we even give a rip if drone reeds enter into a phase-locked state?”
The answer, to me, appears to be that when the oscillators in an isolated system are in a phase-locked state they are in an entropic state, the lowest expression of their energy or work principle.
Why would I care? Because it would take additional energy to get them out of phase. Sometimes quite a lot of energy.
When we jump octaves with uilleann pipes, or alter our bag pressure to humor notes on the chanter it is to our benefit that the reeds will resist a change in phase, and in consequence a change in amplitude. . .part of what gives the impression of wavering drones.
I also suspect (unfounded supposition) that the resistance to changing phase of the reeds also soaks up some of the energy that might contribute to the changes in pitch/
Ok. Back to jigs and reels. 
Bob
It looks like you edited your post while the reply was already in progress. That happens to everyone, including myself, sometimes. Cheers.
For all those that aren´t convinced (“the “mass-distribution” in drone reeds is very different from in metronomes and reeds sit tightly in their sockets”): tongues and strings have a weight, too and are very liable to acoustic waves: Here is a little “experiment” that everybody who passes an acoustic piano can do quickly: Soundlessly press the G-key and keep it held down. Now shortly play a C. The G keeps ringing (silently), though not played at all (and this even only shows the “Quint-relationship”!)
but that’s sympathetic vibration on an overtone series. How is this the same thing as phase locking, which as I understand it is then the wavefronts & troughs of multiple sound sources are perceived as being in alignment ??? 
Just because a vibratory string fundamental has enough energy to induce harmonic motion in a perviously UN-vibrating string is a very dissimilar thing than what happens between two already virbating air columns.
Also I dont see how the metronomes have anything to do with phase locking either. All these results are based on observed perception; and for all we know there could be a ripple in sidereal time that eventually syncs al the metronomes up. By the way, arent there more pressing scientific issues to resolve in Japan these days?? looks like collegiate busy work to me.
Bottom line, are the drones in tune & staying that way, or not? and yes when theyre in tune the get quieter, because there is less air moving.
Okay, time to get really boring. 
When a reed (double or single) vibrates in a closed space, back pressure waves in the reed chamber are created from the variance in flow through the reed (assuming a constant supply of air to the chamber). Pressure (sound) waves within a hollow drone stock, of any practical size, propagates essentially instantly throughout the cavity. Here’s the “back of the napkin” calculations:
Consider that under normal conditions, sound waves propagate at 340 m/s at sea level (only 309 m/s if you’ve landed a gig on the top of Everest). An average main stock might have a drone cavity 10-12 cm from end to end (Geoff and others would have more accurate numbers). This means that a positive pressure wave, caused by the closing of a drone reed (the bass would be dominant if only the bore of the quill is considered), would propagate from one end of the cavity to the other in roughly three tenths of a millisecond (0.00029 sec), corresponding to a frequency of 3.4kHz ( roughly A7 on a piano).
This near instantaneous pressure transfer within the hollow stock constitutes a closely coupled mechanical system. If one of the other reeds (tenor, or baritone) were to begin to open as this positive pressure wave impinged on the reed tongue, it would upset its resonance, thus delaying the opening of the reed until the peak of the pressure wave had passed in a similar manner as the oscillating platform in the video damped the out of sync metronomes until they became synchronized with the platforms oscillations.
dave boling
Yes Dave ? And … ?
Would this have anything to do with “beating” of drones?