The design of a new hall and the control of a variable acoustics hall adress similar problems. In both cases the goal is to optimize, under various constraints, the architectural parameters according to a desired acoustical result. On the one hand, the complex relationships between architectural parameters and the acoustical behaviour of the room limit the efficiency of an intuitive modification or tuning of the room. On the other hand, in spite of their improving prediction performances, room simulation softwares will partly fail as long as they do not include