This paper reports on the evaluation of the speech output component of a dialogue system that enables the control of different home appliances via speech. It was simulated that participants called the system from the car and listened to feedback messages from the system. Their task was to judgethe quality of the systems output while performing a driving task in the TNO driving simulator. The following effects on the quality judgements were studied: type of system prompt (natural, synthesized), transmission degradations (circuit noise, speech codec, packet loss), and the driving task. The results are presented in terms of these aspects.