Architectural and acoustical conditions of an auditorium stage in comparison with a rehearsal room were studied in order to obtain a physical parameter for on-stage acoustics. The basic assumptions are as follows: (1) The auditorium is acoustically divided into two spaces: the stage and the seats. (2) The final aim of designing the rehearsal room is to realize the acoustic properties of the stage. (3) The properties of the sound field for the room are determined by the room's materials, shape, and volume. It is an important fact that their fandamental properties are influenced by the basic architectural conditions. As a result four parameters have been proposed: (alpha) (EDT), ST, RT, and the ts-ratio (between stage and seats). They are shown as representative measures relating to sound absorption and shape in the stage area, volume of the seats, and acoustical similarity between the stage and the seats. In order to check the validity of these parameters, they were applied to the acoustical design of the rehearsal room aiming for the reproduction of the sound field of the stage. The results of these practical examinations show that not only the intended acoustical properties but also the aural impression of the stage were realized by means of sound field control technology ranging from architectual acoustics to electronic acoustics.