The traits that make the best didgeridoos have now been identified, and it has also given us a better understanding of how people use their vocal cords to make sounds with the instruments.
Didgeridoos, used by the Indigenous peoples of northern Australia for at least 1500 years, are “the principal musical instrument of the world’s oldest continuous culture”, say and , both at the University of New South Wales in Australia.
Traditional didgeridoos are made by tapping eucalyptus branches to find “one where hungry termites have eaten a suitable bore”, the pair told the recent in Sydney.
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Part of the branch, usually between 1.2 and 1.5 metres long, is then cut off and its interior cleaned out. As a branch tends to be wider towards its base, the bore is generally slightly flared. The smaller end is smoothed and a ring of beeswax often added.
Although it is just a hollow branch, it produces a range of distinctive sounds that have long puzzled physicists. To investigate, Smith, Wolfe and their colleagues measured the acoustics inside the mouth while three people played a didgeridoo.
Measuring this is difficult because a seal is created between the lips and the instrument, and the sound inside a player’s mouth can exceed 100 decibels.
To overcome this, the researchers pushed a narrow pipe into one corner of each player’s mouth, through which they sent a broadband acoustic signal, a white noise-like sound with many frequencies. This acted a bit like sonar, allowing the researchers to map how the shape of the vocal tract changes while playing a didgeridoo, by picking up the sound again using a microphone in a second pipe.
The team found that the basic low notes that didgeridoos produce come from the player’s vibrating lips interacting with the low-frequency reverberations of the surrounding air, as well as the vibrations produced from their vocal tract interacting with the acoustics of the hollow wooden tube, says Smith. Changes in the sound quality are then made by the player adjusting their vocal tract.
Smith and Wolfe say that a didgeridoo’s pulsating, drone-like sound comes about by players practising circular breathing and reverberating their vocal tracts while they sing and make other sounds.
The best players use their vocal cord reverberations to manipulate the resonances produced by the wood, they say.
“The didgeridoo is quite fascinating,” says Smith. “In one sense, it is one of the very simplest instruments, yet at the lips of an expert, it can produce an astonishing complexity of sound.”
The researchers have also found that these players almost universally favour didgeridoos with weaker resonances at frequencies above 1 kilohertz, as determined by the instrument’s internal environment. This allows the resonances of their vocal tracts to control the sound quality, they say.
But that doesn’t mean there is a set rule about which didgeridoo is best, says Smith. “All players are different, and the biology of one player might be particularly suited to a particular instrument that might not suit another player.”
