The invention relates to a sound system for a motor vehicle and to a process for specifying the functional scope of such. The sound system (1) for a motor vehicle comprises a control unit (2), and several input units (3, 3a) for operating the system (1), as well as display units (4) and several units (5, 11) to generate the source data in the form of sound or video data. The sound data are amplified in an amplifier unit (6), and are conducted to several loudspeakers (7). The units are linked to one another via a bus (8) with a ring topology. Both source data and control data are transmitted over the bus. The functional scope of the individual input units (3, 3a) is specified by means of a priority value of the input units (3, 3a). This priority value is stored in the memory (12) of each input unit (3, 3a). A control command containing this priority value causes the other units of the system (1) to form a priority-dependent functional scope, which represents a subset of the entire functional scope of this unit, and to transmit this back to the respective input unit (3, 3a). The latter then generates its functional scope from the priority-dependent functional scopes that have been conducted to it. This functional scope then comprises all functionalities which can be invoked through this input unit (3, 3a). Since the various input units (3, 3a) have different priority values, they also have different functional scopes. As a result, collisions in the control of the system are essentially eliminated.