THE 'DIDJERIDUO': MUSICAL IMPLICATIONS OF A THREEPORT BRANCHED DUCT

摘要

The didjeridu (or didgeridoo or yidaki), a musical instrument originally played in parts of Northern Australia, is unusual in the extent to which standing waves in the bore and the player's vocal tract are coupled. Skilled players use resonances of the vocal tract to modify the spectral envelope of the output sound, which gives the instrument its unique timbre. The central bore of these instruments is largely produced by termites eating out the interior of small eucalypt trees. This produces a highly irregular and somewhat flared bore, both of which features are important to the performance quality of the instrument. Occasionally a forked section of a tree is suitably eaten by termites. This allows the manufacture of a 'forked didjeridu' or 'didjeriduo' with a branched bore and two available mouthpieces. It is then possible for a single player to produce changes in pitch and timbre, either by adjusting their lip tension to select different bore resonances, or by using the heel of his hand to close the other mouthpiece. It is even possible for two players to play the same instrument simultaneously. Here we present detailed measurements of the acoustic input impedance of a forked didjeridu. Numerical modelling suggests how the presence of a branched duct might alter the perceived quality of an instrument.