How did Schaeffer and Henry route tape signals in the early 1950s for spatial effect?

Routing up to five tape signals to a four-channel speaker system arranged tetrahedrally.

Following World War II, the widespread availability of tape recorders spurred major acceleration in loudspeaker-based spatial sound history, often led by avant-garde composers. Pierre Schaeffer, known for *musique concrète*, alongside Pierre Henry, actively experimented with these new capabilities by the early 1950s. Their setup involved intricate signal processing where they would route as many as five separate tape signals. These signals were then distributed across a speaker system consisting of four channels, strategically arranged in a tetrahedral configuration to produce a tangible three-dimensional sound field over the audience.