Chiff and Fipple Forums

Reed video

A video from Phil Westwell of the operation of a D chanter reed at various frequencies.

Phil playing an early version of his 3D ptinted chanter

David

That's impressive.

What would be interesting would be to test defective reeds (leaky, unbalanced, out of tune, etc.) to see how they react in slo mo. Any acoustic engineers looking for a subject for their master's thesis?

That ... is ... absolutely ... awesome. Thanks so much for posting it.

For the hard D, it clearly demonstrates the double Helmholtz motion that J.-P. Dalmont and G. Le Vey hypothesized in their paper "The Irish Uillean pipe: a story of lore, hell and hard D." (International Symposium on Musical Acoustics, July 2014, Le Mans, France), which I posted in /viewtopic.php?f=6&p=1189888.

I'd like to see how drone reeds act and react, in one setting, since they have to (I assume) act together or somehow synchronize or harmonize. I've always wondered if the bass reed, in a sense, sets the "pace" for the other two since it is so much larger. I'd think the others would have to follow/work together simply in terms of fluid flow.

The soft and hard low D vision almost mimics a beating heart with two pumps per cycle - a main pulse followed by a smaller pulse. It really is the heart of the instrument.

Yes, this video is marvelous. . .but again is only part of the puzzle. Watching this video, and re-reading Patrick Murray's thesis just adds more info. http://www.tuftl.tufts.edu/musicenginee ... n_reed.pdf The video lends more evidence that reeds function as valves. Murray's work gives us a small insight into how to shape a reed to encourage them to properly valve at the correct frequencies.

Bob

Very interesting ,thanks Davy. I must admit there is something very sensual about a throbbing hard D.

RORY

Thank you for posting, BigDavy,

10,000 times thanks for the 10,000 frames per second, very impressing. Confirmes my presumption per 100%.
1. reed closes by air flow
2. air flow stops
3. reed opens again by spring force of cane
4. air flow forces again to close by negative pressure inside the reed and because of air flow round the tip of the reed and because of the frequency/air molecules move in the chanter. This acts like negative pressure on the upper side of an aeroplane wing.

If spring force of cane is too low, than it remains closed after first swing, stucks.

I wonder still what forces the upper octave "a" to breathe double time in comparison to the lower a.
And I wonder is ti the same reason for soft and hard bottom "d".

Ideas?

A simplification perhaps, but this may help ...

Christian Tietje wrote:...
3. reed opens again by spring force of cane

A pressure wave from the prior opening of the reed reflects back from the far end of the bore. When it arrives back, the pressure inside the reed builds up, forcing the reed open again.

Christian Tietje wrote:I wonder still what forces the upper octave "a" to breathe double time in comparison to the lower a.
And I wonder is it the same reason for soft and hard bottom "d".

Ideas?

In the second octave, there are two cycles of the pressure wave in the bore. The pressure wave from the opening-before-last returns to the reed and forces the reed open again.

Hard D is different ... I haven't got my head around that one yet.

Reading Murray's thesis can shed a little light on resonance in reeds. Murray makes reference to a 'cantilevered' surface, and highlights the existence of a 'cut-off' point. What is left in the background is what we know about the resonant surface patterns of plates often called 'Chladny Plates'. Fiddle and violin makers are acutely aware of these, and gauge their carving of fronts and backs to these patterns. When we 'carve' a reed, we are also trying to highlight these resonant surface patterns of vibration. The resonant column of the chanter and the returning pressure waves add yet another level of complexity.

Tunborough wrote: A pressure wave from the prior opening of the reed reflects back from the far end of the bore. When it arrives back, the pressure inside the reed builds up, forcing the reed open again.

I think, that's physically not likely. The frequency arises by a standing wave, not a moving wave. The standing accoustic wave rides on molecules shifting from the reed cane to the first and other lower open holes.

The cane moves by air flow through the lips of the reed tips:
- At the beginning lips are open. No tone.
- Pressure rises by bag pressure or hole to be opened.
- Air begins to move through the tip of the reed.
- Air moves through the hollow part between the two cane halves which is more and more bigger than the area next to the lips.
- By the bigger volume after crossing the lips negative pressure arises.
- Cane will be forced to close by negative pressure inside the two cane halves and still positive pressure from outside.
- By closing of lips the air flow reduces.
- Together with the tension of reed cane the reed opens again
- procedure repeats by a velocity which is exactly the frequency of the tone/of the standing wave

Tunborough wrote:In the second octave, there are two cycles of the pressure wave in the bore. The pressure wave from the opening-before-last returns to the reed and forces the reed open again.

- same happens as above, but double velocity
Am I right?

Very interesting video, always nice to "look under the hood" and see what is going on