Acoustical Description of Uilleann Chanter?

Uilleann Pipes
1

I have to get these pipes out of my head…

Anyhow, at breakfast this morning I was pondering the internal acoustical workings of a chanter. What got me started were some things that I had read about the reed being an extension of the chanter bore. But its not … right. In my chanters the air flow expands from the reed lips to the staple seat and then contracts some to the throat crow, of the chanter, and THEN it expands to the bell mouth. I would love to read about what is happening to the air velocity, pressure, and frequency as it expands then contracts and then expands again. I know that when you expand a passage that you are exchanging potential energy (pressure) for kinetic energy (velocity). I think I know that when you open a passage frequency will decrease (lower note) but I am confused about what the expansion, contraction, expansion is really doing? Why two expansions?


The sad part about all of this is that I was a rocket propulsion engineer and I used to be able to create the Bernoulli theorem equation starting with just f=ma and the law of conservation of momentum. But all of that is mostly out of my head due to years as a manager. And further dulled by 3 years of retirement.

2

Frankly I don’t think Bernouili has much to do with it. Most of the fruitful thinking about woodwinds has come from studying the resonance effects in various chambers. . .shape, size, and apertures. The reed works more like a valve in the sense that it produces pulses, not air flow.
One acoustic description of the uilleann chanter is a ‘stopped conic chamber’. What makes it more interesting is the balancing of various standing waves and their relationship to the vents (tone holes). An added feature (complication) is the reed’s tendency to act as a chladny plate while performing its valving action.
Ok, I’ll get me coat now. . . . .

Bob

3

My preference would be to model it with impedances and a transmission matrix model. I’m getting decent results for whistles. A double-reed mouthpiece is on my to-do list, with a smallpipe chanter my first victim. It may take awhile. Don’t hold your breath.