These “musical towers” are featured in the short film 901: After 45 Years of Working by Eames Demetrios. 901 documents the dismantling of the office of famous U.S. designers Charles and Ray Eames in 1988 following Ray’s death. The Eames office was a kind of maker fantasy-land, with finished and unfinished projects scattered about, meticulously organized tools and supplies, and wonderful little gewgaws in every nook and cranny.
The first few minutes of the film feature a delightful bubbling xylophone soundtrack that is eventually revealed to be coming from these prototype toys designed by the Eameses themselves, and installed in their office for their own amusement.
The towers are wooden boxes six inches square and about 15′ tall, fronted with acrylic, and having sides slotted to accept metal xylophone keys which fit loosely enough to allow free vibration and easy rearrangement. The slots for the keys are angled toward one another, slightly, so that the surfaces of the keys present a series of alternately-sloped platforms for a small hard plastic ball which, when dropped from the top of the tower, will plunk its way slowly down to the bottom, playing a little tune as it goes. The balls are injected using a manual pneumatic piston which shoots them up a pipe to the top of the tower.
There does not seem to be any video of the towers in operation available online, but 901: After 45 Years of Working is available on the first disc of The Films of Charles and Ray Eames, which also includes final and rough draft versions of the classic Powers of Ten. Highly recommended.