To complete this three part blog series on the Didgeridoo, we need to look at the effect of curves in the tube. Actually we don’t need to look into that… but we will see why shortly.
Didgeridoos, because they come from everyday branches or hollowed out trunks of small trees, are not always straight. The same can be said for French horns, trumpets, trombones, tubas, saxophones, and even our own vocal tracts.
Here is the short answer- it doesn’t matter.
Here is a slightly longer answer:
As the frequency increases, the wavelength gradually becomes shorter to the point where any obstruction- even the walls of a curve- can be problematical. In cases such as this, if the wavelength is sufficiently short then it “sees” the wall changes, and reflections and impedance (which is proportional to frequency) increase. This serves to attenuate the sound level in the very high frequency region.
For most everyday things on the macro level (not sure what will happen to nano-sized acoustic pathways) energy below 15,000 Hz is not typically altered by curves in the wave guide. Frequencies above that may suffer some degradation if there is a curve or sudden change in direction.
Grabbing a drinking straw from your friend who is sucking back a summer beverage may not be the wisest thing, especially on a hot day. If you can find a drinking straw that is not being used, then it’s probably safe to grab it. Ideally you should use a straw that has ribs in it that will allow you to curve its pathway.
Try blowing across the top of the straw and gradually bend it this way or that- I am skeptical that anyone would notice any real difference. If there was energy that was produced above 15,000 Hz, then there may be some difference but even the most high fidelity of systems only transduce effectively up to about 15,000 Hz.
Another example is the human vocal tract; have a person utter a sound in the normal fashion with their face aimed forward. Then have them do the same thing while looking up at the ceiling- one may notice a change in their pitch because their neck muscles have differing degrees of constriction (and this may affect the harmonic structure) but the absolute amount of sound energy in the overall spectrum will not be noticeably different.
Didgeridoos, saxophones, bassoons, and brass instruments are quite similar- the bend is partly for aesthetics and partly for ergonomics- it would be difficult to hold a 2 or 3 meter long brass tube without pulling any muscles. And could you image trying to transport such a behemoth on an airplane, or keep it in the cupboard?
Didgeridoos have curves that add to the aesthetics but do absolutely nothing to the sound quality and quantity. If the pitch of the instrument was up in the realm of a dog whistle, then that would be different. Dogs may notice the change but not humans.
Didgeridoos actually come in a portable fashion (seen above) where, like a ram’s horn, the tubing is wound around itself. This makes transportation easier- and although aesthetically to my eye, it looks silly, the sound should be the same as if it was extended out in a straight line.