One day last year at the San Diego Zoo, a female Sumatran rhinoceros named Barakas was singing a mournful, whalelike song punctuated with grunts and moans. Through a window in her indoor enclosure she occasionally rubbed noses with Ipuh, a newly arrived male from Indonesia. Ipuh was munching abstractedly on ficus leaves and looking bored. But animal behaviorist Elizabeth von Muggenthaler, crouching among buckets and hay bales in an adjoining storeroom, was not deceived. She watched the fluttering needle on her tape recorder, which was hooked up to a microphone in Ipuh’s stall, and she suspected the rhino was rumbling--but in a basso so profundo as to be below the hearing range of human eavesdroppers.
The most acute human ear can perceive frequencies as low as 20 hertz. Frequencies lower than that are called infrasound. Unbeknownst to us, the physical world throbs with infrasonic noise, a symphony of deep booms ...
