A mobile unit, such as a robot (12) for example, and a method of controlling a mobile unit are presented. The mobile unit has means of locomotion and is capable of acquiring and recognizing speech signals. If, for example due to its distance from a user (24) or due to sources of acoustic interference (20, 22), the position of the mobile unit (12) is of suitable to ensure that spoken commands from the user (24) will be transmitted or recognized to an adequate standard of quality, then at least one destination location (28) is determined at which it is likely that the quality of transmission or recognition will be better. The mobile unit (12 is then moved to a destination position (28). The mobile unit (12) may determine the prospective quality of transmission for speech signals from a user constantly in this case. Similarly, the quality of recognition may be determined only after a speech signal has been received and recognized. If the quality of recognition or prospective quality of transmission is below a preset threshold, then destination positions (28) are determined for the movement of the mobile unit (12) In one embodiment however, the movement of the mobile unit (12) may be abandoned if the burden determined for the movement to the destination location (28) is too high. When this is the case a message is passed to the user (24).