Simulation of Sound Spectra of Complex Didgeridoo Interior Forms
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Computer Aided Didge Sound Design |
Dr. Frank Geipel
Motivation
Every advanced didgeridoo player will have found that the sound characteristics (toots, timbre, ...) and the playability (back-pressure, responsiveness…) are essentially influenced by the inside form and the material of the instrument. I know many players who are forever searching for a didgeridoo with their ideal sound and playability because of this. Often it’s a very sobering search because very few of the instruments offered on the didgeridoo “market” fully meet one’s expectations. And many of those one-offs that do are also very expensive.This situation prompted me to get into building didgeridoos. I soon found that thorough preparation could put me more than half-way to my goal and spare me many failed building experiments.
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In the didge scene there are opportunities to thoroughly inform yourself about the crafting skills needed to make the instrument. Because I wanted to work with wood, I had the choice between the sandwich method (practised by Eddy Halat, Stefan Thiel, Jan-Ole Haber, Kay Reimer, and others) and the drilling method (practised by Walter Strasser, Johannes Schildkamp and others in several variations). Unfortunately I’ve yet to hear of “trained termites” in central Europe.
Interesting though the drilling method practised by a few craft artists is, I opted for the simpler sandwich method because it allows considerably more complex internal forms to be realised.
While I was researching the methods I got to know some interesting didgeridoo makers, including the Test-A-Doo experimenter, Kay Reimer, whose acoustic experiments impressed me very deeply. I followed his web instructions to make my own first wooden didgeridoo.
Birch wood didgeridoo fundamental tone F# first overblow
A2
2) Using wood
In regard to material properties, I prefer hardwood varieties of high
density and high elasticity (elasticity modules). These are the closest to
eucalyptus and least restrict the higher overtones. For the selection of
suitable wood varieties I have compiled some interesting wood data on our
website which can be very helpful to gauge the resonance qualities and the
ease of working.
Specifically, I use e.g. plum/damson, hawthorn (tends unfortunately to split),
hop hornbeam, hornbeam, oak, yew (heavy, practically never splits, high
elasticity), ash, robinia and birch (medium hard and medium heavy but very
high elasticity).
3) Bore shapes
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How do you achieve suitable didgeridoo interior shapes,
which provide the desired sound characteristics? Here each didgeridoo
craftsman has made his own experiences, which of course commercially
motivated craftsmen will only rarely share. As an interested scientist,
I had the idea of finding such interior shapes through computer
simulation, hence avoiding a multitude of unsuccessful building
experiments. |
Unfortunately research on this topic only provides suitable mathematical
solutions for simple cylindrical and exactly conical tubing shapes (formula
sides 1 and 2).
I was not very interested in these simple, idealized forms, because the
sound characteristics that can be generated in this way are very limited and
are not correct in the case of deviations from these idealized forms.
| I had to find another method! -- > |
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