concepts of drone reed stability

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Philipp
Posts: 31
Joined: Mon Jan 18, 2010 4:20 pm

concepts of drone reed stability

Post by Philipp » Tue Feb 15, 2011 7:06 pm

Hi folks,

I play a half set with plastic drones from David Daye and I produced some drone reeds from aluminium tubing with plastic tongues. I followed the design of the original reeds and found the concept of getting a stable sound by making a "stability bend" in the tongue and moving the bridle quite reasonable.
I then participated in a reedmaking workshop with Andreas Rogge, and, although my reeds were perfectly stable, he made a new reed for the tenor drone to improve the sound. It is made of a cane body with plastic tongue. In fact, the sound is much richer and colourful now and the reed is as stable as the other reeds.
Andreas used a totally different approach. He cut away the edges of the tongue and scraped here and there to make the reed thinner at some spots. I also used straight tongues, whereas David and Andreas use tapered ones.

My question now is, if anybody could tell me something about the physical background of these two concepts. I'd like to understand what the scraping, bending, adding weight etc. does, especially in terms of pitch and pressure stability. If you have a certain point at which a drone reed is stable, how can you then influence the tone?

Cheers,
Philipp

ps.: I have used the search function but didn't find anything that explains what I'd like to know, so I hope this isn't a double post.

outofthebox
Posts: 630
Joined: Fri Oct 30, 2009 2:02 pm

Re: concepts of drone reed stability

Post by outofthebox » Thu Feb 17, 2011 8:04 am

I have no experience of composite drone reeds - though I have it in mind to try to make some inverted composites some time. Here's a link that you might find helpful.

http://www.raysloan.com/Uilleann%20Maintenance.html

Philipp
Posts: 31
Joined: Mon Jan 18, 2010 4:20 pm

Re: concepts of drone reed stability

Post by Philipp » Wed Feb 23, 2011 1:46 pm

Thanks for your help, but I already knew most of this. I was looking for much more theoretical information on WHY things happen, when you do this and that with your drone reeds.

Cheers,

Philipp

LiamO'Flynn
Posts: 149
Joined: Sun Mar 08, 2009 12:53 pm

Re: concepts of drone reed stability

Post by LiamO'Flynn » Thu Feb 24, 2011 4:52 am

Andreas Rogge was probably trying to enhance the modes of vibration of the reed tongue by making it more flexible at the antinodes. The first mode of vibration is the obvious one where the tongue moves back and forth with the node at the base and the antinode at the end. In the second mode the antinode is at approximately 50% along the tongue and in the third mode they are at 32% and 68% along the tongue. Cillian O’Brien gets around this by cutting the tongue so light and flexible ,it is on the point of being flimsy ,but it makes for very rich sounding drones.

Liam
Liam O'Flynn the plumber not the piper .

verdatum
Posts: 18
Joined: Wed Jan 05, 2011 12:39 pm
Real Name: Paul Grodt

Re: concepts of drone reed stability

Post by verdatum » Thu Feb 24, 2011 12:11 pm

It sounds to me like you are asking about the physics involved. In which case, it gets pretty complicated, pretty quickly. Musical acoustics of reed instruments covers concepts like the mechanics of oscillating elastic beams, and gets into some of the more complicated aspects of compressible fluid dynamics. Taking all of that research, which is mostly in the form of physics journal and musical acoustics publications, and converting it into "should I shave down my reed tongue here, or here?" is pretty rough. The result is as you've seen: most reedmaking techniques are instead the result of a combination of inherited experience and trial & error. Experienced reedmakers will understand the effect of various changes to a reed, but the real "Why?" of it all is often seen as overly complicated and only marginally useful (forgive me for overgeneralizing).

That being said, I've found myself trying to learn all that crazy stuff anyway. I only got up to physics II in college, so I'm picking up the fluid dynamics and mechanical physics as I go. I started with a text called "Fundamentals of Musical Acoustics" by Arthur Benade, but since that text covers such a broad scope, it only covers reed physics to a certain depth. Otherwise, Google Scholar is your friend.
Pennywhistle: A dangerous gateway drug.

billh
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Re: concepts of drone reed stability

Post by billh » Thu Feb 24, 2011 5:16 pm

I think you can get all the behavior by just considering the tongue to be a simple oscillator.

Thus weighting the tongue near the tip, increasing the amplitude of the oscillation by opening the tongue, lengthening the tongue, and/or reducing the stiffness by scraping at the base of the tongue drop the frequency; lightening the tongue by scraping near the tip, reducing the amplitude by closing the tongue, shortening the tongue, and leaving the tongue stiffer all raise the frequency.

If the reed is working well, the first mode should dominate, but other modes are in theory present, as the motion of the tongue is not sinusoidal - you should get a waveform with very square edges - maybe more like an impulse or square wave. If the second mode starts to dominate you'll get squeals and near-octave jumps (sometimes a misbehaving bass drone will do this, for example).

If you consider the reed just a simple oscillator, the drone is a coupled system. The more compliant the quill is, the less it will perturb the frequency of the air column itself, which is a good thing (otherwise you tend to get too much pitch drift with pressure). Since a super-compliant drone quill may be fragile or impractical, the next best thing is to match the frequency response of the drone quill in some way with the desired frequency of the air column. At that point I think in the real world it becomes a trial and error process, at least until one gets to know the preferences of a particular drone design.

Bill

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