Traditionally, the room acoustic properties in an ordinary public room are defined by only one parameter, the reverberation time. However, research has showed that additional room acoustic parameters as sound strength and speech clarity are necessary to consider in order to achieve good acoustic conditions. In a room with acoustical ceiling treatment the effects of furniture and interiors on the room acoustic parameters are significant. In addition, by using diffusers with directional properties it is possible to individually control the room acoustic parameters. Room acoustical measurements have been carried out in a reverberation chamber with suspended absorbing ceiling and directional diffusing objects. The effect of different diffuser configurations has been examined regarding reverberation time, speech clarity and sound strength. The evaluation shows that the orientation and the amount of the diffusing elements have a significant influence on the room acoustic parameters and can be used to fine-tune the acoustical conditions in public ordinary rooms with an existing acoustic ceiling treatment. This paper presents a study showing how diffusers can be used to contribute to an improved sound environment in public ordinary rooms with an acoustic ceiling.