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Didjeridu acoustics

This page gives a brief introduction to the acoustics of the didjeridu (sometimes spelt didgeridoo, and known as yidaki or yiraki in the language of the Yolngu, one of the peoples of Northern Australia, where the instrument originated). The didjeridu/yidaki is a remarkable instrument because of the wide variety of timbres that it produces. Further, it is of more general interest because it is the most evident example of the interaction between a wind instrument and the vocal tract of the player. These interactions are important to good playing of any wind instrument, but to the didjeridu they are central, so this page concentrates on discussion them. We also use this page to report the results of a research project, so some preliminary scientific papers are linked below. The project involves five researchers from three institutions:


Alex Tarnopolsky [1].Neville Fletcher[2], Lloyd Hollenberg [3], John Smith [1] and Joe Wolfe [1].

[1] The University of New South Wales, [2]The Australian National University and [3] The University of Melbourne.




Lloyd Hollenberg (left), physicist and didjeridu player, managing to play the didjeridu while having the acoustic properties of his vocal tract measured. In the sound clip below, Lloyd demonstrates several didjeridu effects produced by changes in the shape of the vocal tract configuration (moving tongue and jaw) and by vocalisations (vocal fold vibration) on top of a drone with a fundamental at 71 Hz (~C#2). Ben Lange (right), is a student and didjeridu player who is also working on this project.

mp3 file 470k . . . Download didj sound file in .wmp3 format (470 k)


How does such a simple instrument make such a variety of interesting sounds?

The instrument is deceptively simple: it is just a wooden tube, about 1.2 to 1.5 m long, hollowed out by termites in the thin trunk of a eucalypt tree, and with a ring of beeswax around the mouthpiece for sealing and player's comfort. It acts as a closed pipe, and its shape, though irregular, is roughly that of a truncated cone, usually with a small flare, so that it is not very different to a cylinder. The second resonance is about a 10th or 11th higher than the fundamental, but overblowing is not very important in most playing techniques. Further, because the resonances usually have no harmonic relation to each other, the instrument geometry is less important to the sound than is the case in other wind instruments. Because the player's lips control the air flow, it is classed as a lip-reed instrument, as are tuba, trumpet etc. The operation of this family is discussed in Introduction to brass acoustics.

What makes the didjeridu's sound so interesting and varied is the very strong and varied interactions among
*    the sound waves in the instrument,
*    the motions of the player's lips and
*    the sound waves that are produced in the player's vocal tract.


A schematic diagram of the acoustic system (not to scale).

The standing sound waves in the didjeridu itself are qualitatively much like those in other lip-reed instruments and so are understood reasonably well. There are however considerable differences from other lip reeds due to the rather irregular shape and surface roughness, and to the fact that the resonant frequencies are not harmonic. The sound waves in the player's vocal tract are strongly influenced by the resonances of the tract itself, which are modified by the player during performance, and to the way these resonances are excited by the regular openings of the lips and the sound waves in the instrument. In turn, the regular opening and closing of the lips is determined by the difference in pressure between the air inside the lips and outside the lips (which includes the effects of the wave in the didjeridu), along with the pressure variations due to air flow and, of course, the muscular tension in the lips themselves. Sometimes the sounds also involve vocalisations--sounds made by vibrations of the player's vocal folds, as in singing. The waves produced by the vibrations of the vocal folds can interact with the those generated by the lip vibrations in nonlinear ways to produce complex sounds. In short, a simple instrument, but lots of interesting sounds--and interesting physics!

Playing the instrument requires circular breathing. For most of the time, the player exhales through the mouth in the ordinary way, but, when new air is needed, the cheeks are filled with air, the soft palate is used to isolate the mouth from the respiratory tract, and the air in the mouth is used to continue playing by contracting the cheeks. Meanwhile, the player inhales quickly through the nose. This requires coordination--and a lot of practice. The result is an uninterrupted sound from the instrument. The timbre changes: during the normal part of the cycle, the whole vocal tract is connected via the lips to the instrument. During the inhalation, only the mouth itself is involved. There are great differences in the resonances in the mouth for these two configurations, so the timbre of the sound produced changes dramatically. Far from being a disadvantage, players use this timbre difference, along with differences in loudness, to establish the rhythm of the performance. For more about the resonances of the vocal tract, see our site on vocal tract acoustics.



The spectrogram of the same didjeridu sound clip linked above. A strong formant is indicated by the patches of light colour. These are changing with time as Lloyd changes the shape of his tract.

mp3 file 470k

More to come. This project is just beginning and we shall be adding more physics, pics and sounds to this site in the future.

More detailed information on didjeridu acoustics (reproduced with kind permission of the editors).


Fletcher, N., Hollenberg, L., Smith, J. and Wolfe, J. (2001) "The didjeridu and the vocal tract" Proc. International Symposium on Musical Acoustics, Perugia. D.Bonsi, D.Gonzalez, D.Stanzial, eds, pp 87-90. (.pdf file)
Hollenberg, L. (2000) "The didjeridu: Lip motion and low frequency harmonic generation" Aust. J. Phys. 53, pp 835-850.
Fletcher, N.H. (1996) "The didjeridu (didgeridoo)" Acoustics Australia, 24, pp 11-15.(.html link)

Links for the didjeridu/yidaki and related material


Dreamtime : a repository of information and links about the didjeridu/yidaki
Google's web directory of didjeridu/yidaki sites
National Aboriginal Islander Skills Development Association
A collection of resources from a commercial retailer.

Alex Tarnopolsky [1].Neville Fletcher[2], Lloyd Hollenberg [3], John Smith [1] and Joe Wolfe [1].

[1] The University of New South Wales, [2]The Australian National University and [3] The University of Melbourne.




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