An installation in Sydney, Australia's Pitt Street Mall consists of person-shaped, LED-filled sculptures that use proximity sensors to sing beautiful music when people pass by.

Called the Infinite Choir, it consists of two rows of abstract human-shaped sculptures with speakers instead of heads that sing when people walk by. But it's a far cry from the twee Christmas carols: each of the 16 "singers" (eight per row) is fitted with a pre-recorded voice that sings an angelic, wordless phrase.

An ultrasonic proximity sensor in each sculpture will trigger when a person comes close, playing the vocal recording and, if you're visiting at night, a color-changing display of LEDs beneath a translucent shield. The more people who are interacting with the installation, the more intense the sound and display -- encouraging passersby in the perpetually busy mall to slow down and take a look.

The approximately $245,000 installation was commissioned by the City of Sydney and built by Iris and Eness as part of a three-year contract (PDF) to provide Sydneysiders and visitors with a "magical Christmas playground."

The Infinite Choir will perform in Pitt Street Mall until December 25, so if you're nearby, head over and have a listen.