On June 19, 1950, the research of José Bernhart and Jean Wilfrid Garrett on the stereophonic broadcasting system resulted in the first stereophonic broadcast on the RTF of Une larme du diable (A tear of the devil). This radio drama was written by Théophile Gautier in 1839. In order to benefit from stereophonic listening, the auditors had to set two radios, tuned to two different channels. The radio adaptation of the play by Jean Forest was broadcasted under the artistic direction of René Clair. “By which artifices could we have represented in the theater, beings, things or substances devoid of gravity which take shape only thanks to the prestige of poetry? It was not until this day and to imagine these devices, it is the radio that provides us the secret.” To René Clair the radio was almost the only medium that gives the possibility to stage the imaginary and the poetry of Une larme du diable. The sound images are developing and become rich and more sophisticated thanks to the recording techniques which use an artificial head for the recording and the stereophonic broadcast on the radio. The different and distinct sound spaces, through the radio play are superimposed on the listener’s domestic space, and an ensemble thus forms from what we could define as a sonic cospatiality. Other forms of sonic cospatiality are also present in different steps in the creation of radio plays. A variety of sonic spaces are produced by sound recording, placement of radio sources, and the space of the “imaginary scene” of the listeners. This research describes the technical modalities of recording on the radio and stereophonic sound diffusion, which leads to a sonic cospatiality.