Double stars and trumpets on a train - the Doppler Effect

As the system is turning the emitted sine waves are compressed and expanded depending on the rotational speed and the length of the strings resulting into a vibrant sound field. This effect was predicted in the mid 19th century by the Austrian Christian Doppler for the changing colours of rotating double star systems. But the proof of principle at that time was not realized with light physics, but with acoustics: Christopher Buys-Ballot installed 1845 trumpet players on a steam train in the Netherlands. In fact the approaching trumpets appeared to play at a higher pitch, whereas the pitches did sound lower by the receding band.  

The Heaven's Carousel connects literally to this experiment. Instead of a brass band it uses simply loudspeakers playing sine waves. With the growing speed of the rotating loudspeakers the Doppler effect becomes more and more apparent. This is why the visitors are invited to move around under the installation to explore the astonishing fact that there is no Doppler effect in the middle of the installation, but the more they move outwards the effect becomes apparent.
Here is an audio record moving slowly from the center out of the carousel (2 min.):

excerpt from the finale of Prelude 2 standing in the middle and outwards (ca. 35 sec.)

Learn more about the Doppler effect in the correspondent Hubblecast: