One factor that seems to influence an individual's effectiveness in requirements engineering activities is her knowledge of the problem being solved, i.e., domain knowledge. While in-depth domain knowledge enables a requirements analyst to understand the problem easier, she can fall for tacit assumptions and fail to consider issues that she believes to be obvious. This paper investigates the impact of domain knowledge on requirements engineering activities. Its main research question is "How does one form the most effective team, consisting of some mix of domain ignorants and domain awares, for a requirements engineering activity involving knowledge about the domain of the computer-based system whose requirements are being determined by the team?" For completeness, a number of other factors, such as educational background, are considered for their effect on teams' effectiveness. Two controlled experiments test a number of hypotheses derived from the question, including mainly that for a computer-based system in a particular domain, a team consisting of a mix of requirements analysts that are both ignorant and aware of the domain, is more effective at requirement idea generation than a team consisting of only analysts that are aware of the domain. The results show no significant effect of the mix by itself on effectiveness in requirement idea generation. However, the results do show surprising significant effects of the educational background and of the mix combined with the educational background. Combining the results, the main conclusion is that the presence of a domain ignorant with a computer science or software engineering background improves the effectiveness of a requirement idea generation team.