The “Espace de projection” (ESPRO), the variable acoustics performance hall of Ircam, was designed and built for providing the largest variability possible with regard to form, volume, and acoustical properties. The walls and ceiling consist of individually rotatable prisms with three different material surfaces to absorb, reflect or diffuse the incident sound. To vary the hall’s volume and shape three ceiling panels can be raised or lowered independently, and a roller curtain allows for separating the different volumes. Despite the remarkable flexibility of this room a surrounding 350-loudspeaker array has been recently installed that aims at varying and controlling the acoustics to a greater extent than is possible by passive variable acoustics. Higher-order Ambisonics (HOA) provides the means for creating immersive 2D/3D audio scenes including reverberation and environmental effects. This article reviews the theory with regard to the installation of a HOA array in the ESPRO. The discussion will be mainly focused on the definition of a feasible grid of loudspeakers and the design of HOA decoders in order to overcome the practical limitations of using non-uniform loudspeaker arrays.
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