When the working day is done, I can usually be found writing fiction from the comfort of home. Currently, I’m working on a story about the relationship between a mahout and his elephant. I’m still largely in the research phase, which means my early morning hours are now saturated with all things elephant.
So, what does this have to do with audio?
One of the most interesting things I’ve learned about elephants is the way they communicate with each other. Elephants can “speak” to each other over long distances by producing and receiving infrasound, a sub-sonic rumbling, which can travel in the air and through the ground much farther than higher frequencies. The frequency range in which humans can hear sound is 20 Hz to 20 kHz. Sounds are generally considered to be infrasonic if their frequency is less than 20 Hz. This low frequency sound can’t be heard by humans, but it can be felt. This is how our subwoofers allow you to feel bass rumbling through your body during an epic battle scene. They go infrasonic. For instance, our flagship Digital Drive PLUS series produces frequencies as low as 8.8 Hz overall (14.4 Hz +/- 3 dB).
These infrasonic frequencies can also be felt by the sensitive skin of an elephant’s feet and trunk, which pick up the resonant vibrations much as the flat skin on the head of a drum. To listen attentively, every member of the herd will lift one foreleg from the ground, and face the source of the sound. They will often also lay their trunks on the ground, as well. The lifting of one leg will presumably increase the ground contact and sensitivity of the remaining legs.
The discovery of this new aspect of elephant social communication came with breakthroughs in audio technology, which can pick up frequencies outside the range of the human ear. The pioneer in this type of research is a woman named Katharine Payne. Payne is a researcher in the Bioacoustics Research Program at the Laboratory of Ornithology at Cornell University. In 1999, she founded the lab’s Elephant Listening Project. The Bioacoustics Research Program team developed Autonomous Recording Units (ARUs), which are used to continuously record elephant vocalizations in forested areas. These units are hoisted high into trees, protecting them from elephant damage. They are waterproof and will record unattended for up to six months. The ARUs have performed extremely well in the difficult climate of Africa’s tropical rainforests. Reportedly, the biggest problem has been damage to the power cables caused by inquisitive chimpanzees.
In 2004, Payne’s initial recordings of elephants were selected as one of 50 recordings chosen that year by the Library of Congress to be added to the National Recording Registry. Incidentally, I highly recommend taking a look at the list of recordings on record. It might surprise you to see what else is there.