Occasionally, pipers and pipemakers talk about this so I thought I would try and work out how fast a reed head does move (i.e. opens and closes). I imagined that they must move fast because, when I look at a moving reed all I can see is a blur, at best. But it seems that the head doesn’t move fast at all:- well under 1 mph and possibly a bit faster for higher notes.
I don’t know if this is right so maybe someone who really knows could comment?
If you are playing an A, the lips will open and close 440 times in one second. In the second octave, it will move twice as fast.
I find it hard to believe that the opening frequency of the reed lips should be influenced by the fingered tone.
The actual tone is not only defined by the frequency of the tone generator but to a great extent also by the length of the vibrating air column which in turn is defined by the length of the chanter and the open fingerholes.
The frequency for back D would be 587 Hz, so the opening frequency of the reed must be higher than that.
Most CP chanter reeds produce a tone near G# when blown (or sucked) without the chanter, which would be a frequency of 831 Hz.
This still can not be the frequency generated at the lips of the reed, because the reed length acts as part of the air column.
If we assume 80 mm as average reed length, and use these 80 mm as λ/4, this would lead to a frequency of roughly 1050 at the reed lips.
This is all without any claim of accuracy, I am not a physicist, and it is more than likely that I forgot a few very important things!
Just a few thoughts on the matter…
Ha! It just goes to show how wrong I can be!
I wonder who’s chanter and reed he used?
It’s my understanding that Patrick Murray was involved with The Uilleann Pipeworks of Boston.
Of particular note is the fact that reeds display very complex contortions as they go through their vibrational regimes. They are a very specialized example of plate and membrane harmonic motion. But then we already knew they were complicated and ornery 
Bob
http://www.tuftl.tufts.edu/musicengineering/research/uilleann_pipes/uilleann_reed.pdf
Yeah, but how fast does the reed head move? Or, to put it more precisely, what is the combined speed of those two pieces of cane as they come together and then move apart?
I think my question was analogous to asking “how fast am I walking down this street?” whereas I think the thesis on vibrations is trying to tell me how fast my left and right hands are moving (relative to the earth’s surface) as I swing my arms back and forward as I walk down the street.
If I know for how long I walk down the street and how many equally-spaced street lamps I pass then shouldn’t I be able to work out my speed? I would have to know the distance between the street lamps, of course.
Perhaps I should leave this kind of stuff to the “science guys”. I think the ones with the heavy-rimmed spectacles are the best!
My guess is that the distance traveled per second by one of the blades will be easier to determine for a low frequency note like the bottom D. Notes in the second octave will be rather difficult to calculate since, presumably, the higher pressure on the blades will cause them to flex inwardly, thereby reducing the open elevation by an indeterminate amount.
If you want the speed in MPH, that would be easy enough to figure. If it vibrates 440 times a second, you just need the distance between the blades. If its 1/16th of an inch, then it travels 1/16 of an inch in 1/440 of a second. Now just convert to miles per hour…
Patrick Murray did some interesting observations in his thesis work but it doesn’t give much information regarding the OP question.
As there is a lack of information in the literature on Uilleann reeds a good first approximation would be an Oboe reed, an instrument that seem to be far more interesting for the scientific community 
The closing time of an Oboe reed can be assumed to be around 1 ms, the opening time for the same reed would be around 1-3 ms (shorter for higher frequencies). With the assumption that the distance traveled by each reed blade is about 0.5 mm (1 mm opening), the “ reed speed” isn’t that high , < 1 m/s. However, as the distance is short this vibration would be difficult to detect without the use of a high speed video recorder (+ 2000 fps).
For those interestead:
Sandra Carral (University of Music and performing Arts, Vienna ) has made some great contributions in this area, among others.
Numbers above from this publication
Also, André Almeida’s PhD thesis work is a very good source of information with a lot of useful references.
http://goios.free.fr/these/ThesisAlmeida-Draft22052006.pdf
/M
Interesting stuff Marcus - thanks for the links. And the business of the flexing of the blades is significant I’m sure, Uillmann.
It seems to me that there are some other phases in the cycle as well:- the time that the blades are closed - partly accounted for by the time it takes the sound wave to go up and down the tube but perhaps some “down-time” as well (i.e. inertia). Perhaps there is some inertia on the other side of the cycle as well (i.e. the blades are static and open for a moment whilst they recover and start to close).
I can’t stop thinking about this discussion for some reason.
I’ve attended piping seminars (tionols) where Scottish border pipes, small pipes, etc. were featured, e.g., The Pipers’ Gathering and the Upper Potomac Pipers’ Weekends. Out of curiosity, I watched and talked to the other pipers about their instruments and playing. One thing that I gathered is that they aim to play at a constant pressure and rely solely on the finger holes to produce notes. (Some even use a manometer to train their handing of the bag to maintain this constant pressure.)
So, I inferred by analogy that we do more or less the same but can shift to a higher octave by increasing the pressure. I am aware that we also use different pressures to achieve certain variants of notes, e.g., hard D, Cnat, etc. but by and large I thought that we did this by manipulating two pressure zones (corresponding to the two octaves) and our fingering did most of the rest. I also imagined that the reed speed was probably 440 and 880 Hz, respectively.
My question is: what is the dynamic between fingering and the notes produced? I.e., when we play higher notes we make the chanter “smaller” by opening holes up its length. Are we also increasing pressure to raise the fundamental frequency of the reed to help this effect, or does the changed chanter characteristics do this, i.e., cause the reed to vibrate more rapidly.
I’m not a specialist in this area so take this with a grain of salt. When the chanter is producing a note the reed and air column in the chanter are a coupled system, they don’t work independently of one another. What I mean is, the reed has the ability to vibrate at different frequencies–it’s the air in the bore and the boundary conditions there (i.e. what holes are covered) that ‘tell’ the reed what vibrations are ‘allowed’. In a simple system like a string vibrating, the frequencies allowed have to do with the length and mass of the string, but basically half of the wavelength needs to fit an integer number of times into the total length of the string. The lowest frequency vibration (fundamental mode) has a wavelength twice as long as the total length of the string. I assume there is an analogous idea with the waves in the air column, setting the allowed frequencies. The reed vibrates in a way that sets up an air pressure wave “allowed” by both the chanter and the reed. Vibrations that are not allowed are damped (killed off) very quickly. It’s a pretty complicated system though (the reed itself, conical bore, etc.) so I’m sure there’s more to it than that. I think Bill Haneman made a set of slides on some basic acoustics for pipemakers and others interested in this, it might be on his website.
Fascinating! Thanks.
Uillmann you were correct the first time. The reed blades open and shut only once per fundamental note, but because the motion is not sinusoidal, it includes the higher vibrational modes as well. (See Priciple of Superposition).
Some of the modes - possibly most of them - discussed in the Murray thesis should not occur when the reed and chanter are working correctly, but they may account for some of the awful squeaks.
Ha! It just goes to show how wrong I can be!
You do know Cunningham’s Law: the quickest way to get the right answer on the internet isn’t to ask the question, it’s to post the wrong answer.
Are there any other links to studies on the physics of double reeds? I actually find this really interesting and it could be an asset to reed making when I finally get around to it.
I remember finding one or two a while back. I’ll do another search today and post what I find here.
Edit: I will list some articles here if any science/engineering nerds want to check them out. I also included some stuff on bore acoustics. If you don’t have institution/library access to these journals you can send me a PM. Some of them are free, though.