The science behind the didgeridoo
When you hear the sound of the didgeridoo, it might make you think of the Australian outback.
The first long drone like the sound of the dusty plains. Then suddenly a kangaroo hops by, followed by a little joey. The kookaburra laughs and the dingo howls. When a didgeridoo is playing, it almost sounds like the Earth itself speaking.
So what’s the secret (and science) behind the magic sound of the didgeridoo? We got in touch with Associate Professor John Smith from the University of New South Wales. As a researcher in acoustics and physics, John shed some light on this iconic Australian instrument.
How is it made?
A didgeridoo could almost be considered made by nature. Hungry termites gnaw out the insides of a young eucalyptus trunk. Once you cut it down, you have a didgeridoo.
“A traditional didgeridoo, it’s usually made from a fairly narrow eucalyptus trunk that’s been hollowed out by termites,” John tells us.
“People would go around, maybe hit likely looking branches with a boomerang, see if they have the right sort of sound. They’ll then cut it off … and blow it to see if it sounds OK,” he says.
If it’s good to go, it’ll be cleaned out and finished off with a beeswax rim to make it more comfortable to play.
This is how traditional didgeridoos are formed, but modern ones could be made from a range of materials. Plastic, aluminium and different types of wood can all be used to make a didgeridoo.
How old is it?
This is a tricky one to answer. Being made of wood in termite country makes it hard to withstand the test of time.
When termites first chow down on the eucalyptus, they’ll leave the outer shell. This is because they can’t stand being exposed to the open air. But if that shell is buried in sand or otherwise covered, they’ll quickly go back to finish the job.
“The trouble with establishing the history is they’re made by termites, and as soon as you drop one on the ground, the termites go back to eating them,” John says.
“So they don’t last. You can imagine if they were buried with someone or discarded, they’re gone.”
Without any artefacts to date by, it’s hard to know how old they are. Some say there is rock art that dates the didgeridoo back at least 1500 years, but it’s possible that they are a lot older.
How is it played?
The technique for blowing into a didgeridoo is very similar to modern day trombone playing. You blow air through your lips like a raspberry.
“As the air goes between the lips, it sort of pushes them apart, but then a force called the Bernoulli force and also tension forces on the lips makes them close again,” John says.
“So lips open and close rapidly, and the rate at which they open and close is determined by the didgeridoo itself.”
But correct blowing alone will only deliver one note. The rich sounds of the didgeridoo actually come from a combination of the instrument and the player’s vocal tract.
“The didgeridoo is quite an unusual instrument, and it’s an instrument where the vocal tract is most strongly coupled to the instrument and can be used to vary the timbre of the sound,” John says.
“A further complication is that while [someone is] playing the didgeridoo, they can also be speaking or singing or making sounds with their vocal folds as well.”
This is how a player imitates animal sounds.
“The sound that you then hear is actually two things: it’s the didgeridoo plus the sound of their vocal folds going through the didgeridoo,” he says.
“These can interact in a very complicated way to produce quite complex sounds.”
What is cyclic breathing?
When people discuss the didgeridoo from a science perspective, they often talk about cyclic breathing.
Cyclic breathing is what allows didgeridoo players to play for long periods of time. Playing a didgeridoo requires a constant stream of air being pushed through the instrument, but players don’t stop to take a breath. This makes it seem like they’re able to breathe in and out at the same time.
Of course that would be impossible. What’s actually happening is they’ve come up with a technique to store a supply of breath in their cheeks they can use to blow out. Since they’re not breathing out through their lungs, they are free to take in short, sharp breaths through their nose.
“What happens is you have a deep breath and then you close the soft palate at the back of your mouth,” John tells us.
“Now your cheeks still continue to contract and express air through the didgeridoo. At the same time, you have a very rapid intake of breath through your nose, which fills your lungs up.”
It takes practice to get it right, but once mastered, the cyclic breathing technique will allow a player to play for much longer.
Some modern trombone players and other musicians have since adopted the cyclic breathing technique to enhance their own performance.
This traditional instrument, possibly one of the oldest in the world, continues to influence music not just across Australia but around the world.