Acoustic wind pavilion makes music out of thin air

The Aeolus Acoustic Wind Pavilion

Aeolus, a fascinating acoustic wind sculpture made by prolific Bristol artist Luke Jerram, is as much a feast for the ears as it is for the eyes. Named after the mythical Greek ruler of the four winds and built in conjunction with the University of Southampton's Institute of Sound and Vibration Research and the University of Salford's Acoustics Research Center, the giant aeolian wind harp is intended to inspire the public to learn more about the amazing things that can happen when engineering, acoustics and aerodynamics are blended together.

"The Aeolian harp is a quite mysterious sound, really," said Jerram. "I think the Victorians were very excited by it just because it sounds quite unearthly - it almost sounds like the aliens landing. It's quite mysterious and quite beautiful. And it's also quite hard to predict - it's hard to predict the sound that's going to be produced from our string. It's just created by the string vibrating in the wind."

Jerram got the idea for the wind harp after speaking with desert well (qanat) diggers while on a visit to Iran several years ago. "They basically go out into the desert with an axe and they draw a circle in the sand and then they dig straight down into the sand and into the rock," he said. "When they hit the water table, they then dig across and create these incredibly long tunnels transferring the water out of the desert into the town. They might then dig air vents sort of maybe every 50 meters."

Schematic of a qanat desert well which helped inspire Jerram to create Aeolus

The diggers described how when conditions are just right, the wind can make those vents "sing" and make noises. This gave Jerram the impetus to explore other structures that might use the wind in a similar manner, and eventually, his version of this ancient musical instrument was born.

The Aeolus and other wind harps make their music through a phenomenon known as the von Kármán Vortex Street effect in which wind blowing across a string or other thin, rigid object creates an alternating series of vortices downstream that sets up a vibration in the object. The pitch and volume of the sound generated by the effect is random and is determined by the strength and speed of the wind as well as the length and thickness of the string.

Artist's interpretation of the von Kármán Vortex Street effect

Jerram's harp is composed of 310 stainless steel tubes that terminate in a double-curved arch (picture a section taken from a sphere) which visitors can enter for a unique audio-visual experience. Polished to a mirror finish internally that reflects the changing weather conditions, in musical mode, many of the tubes are connected to strings attached to a membrane or "skin" on their outer end that transmits wind-generated sound into the arch and to listening posts situated nearby. Even on windless days, the tubes without strings hum at low frequencies, enhanced by an acoustic lens effect that focuses the sound directly at observers in a specific point under the arch.

Until May 10, 2012, the Aeolus, which has been traveling about the UK since its completion last year, can be experienced at its location in Canary Wharf, London. Eventually, Jerram hopes to sell Aeolus and find it a permanent home where it can continue to delight the public for many years to come.

Source: Luke Jerram