Interesting Acoustic Properties at Chichen Itza

Tourists delight in the strange chirping echoes they produce when they clap their hands at the base of the steep staircases that sweep up the face of Kukulkan, a 1,300-year-old Mayan pyramid in the Yucatan. While amusing themselves, the tourists may unwittingly be replicating an ancient Mayan ritual, says David Lubman, an acoustical consultant based in California. The echoes are eerily reminiscent of the call of the quetzal, a bird the Maya considered a representative of the gods. Lubman recorded the enigmatic echoes while on vacation in Mexico and analyzed them when he returned home. The echoes sound like chirps, he realized, because the sound from the tapping doesn't hit a solid wall but hundreds of small steps, producing hundreds of echoes. The difference in the distance traveled by echoes bouncing off lower steps is rather small, so the echoes follow each other closely and make a high-pitched sound; the distances and intervals between successive echoes returning from the higher steps, however, are longer, so their pitch is lower. When the echoes reach a listener's ear, the change in pitch sounds like a chirping bird. More...