The acoustic and musical relationship with architectural space has a long history: ancient Greeks, the Romanesque Middle Ages, and the Renaissance, for example, utilized it in various ways. Electroacoustic composition on a support (acousmatic music), with its deliberate choice of “nothing to see,” and the acousmonium as an instrument for spatialized performance, serves as a laboratory for researching space as a musical element both during composition and as the principal agent of performance. Four categories of space emerge from this particular practice of interpreting and understanding the acousmatic repertoire: ambiophonic space immerses the listener in a sonic ‘bath’, source space localizes sounds, and geometric space structures a work in planes and volumes. These three categories most often pertain to multiphonic pieces. The fourth, illusion space, is consciously or unconsciously addressed in works in a stereophonic format, which create the illusion of depth of field through two loudspeakers. A few examples, diagrams, and explanations demonstrate how various spatialization systems are designed, particularly the acousmonium as designed by François Bayle in 1974. The performance of an acousmatic work tends to connect various spatial figures that reinforce the composition’s writing, highlight existing figures, or create new ones. Stereophonic works offer the performer greater freedom of choice. Sixteen figures are listed, along with their musical function. Depending on the character of each piece, a different spatial approach can emphasize one aspect of the composition over another: icons, movement, unmixing of polyphony, phrasing and variations, subjectivity, and matter. Thus, we can observe the significant role of the ‘spatializer’ and the necessity of their active presence in concerts. We witness the emergence of a new musical profession with numerous other applications. The spatial writing of multiphonic works also employs these figures in the studio. Some software is dedicated to this function, but multichannel control is essential in the studio. Lastly, figuralism, by playing with spatial figures, appears to be a key approach to giving meaning to and justifying space as an element that enhances the expressiveness of musical works. Annette Vande Gorne’s opera Yawar Fiesta is an exploration of this topic. The spatial projection of music for acousmatic listening – sound in space – opens up the future space to a fifth dimension of expressive music: the Space of Sound.