There is a need for a greater understanding of the acoustical and airflow performance of interior openings, and of silencers implemented to improve their acoustical performance, in naturally ventilated buildings. This paper discusses preliminary, fundamental aspects of a study done to provide engineers and architects with optimal design techniques. It discusses the characterization of ventilator performance, including the definition of the open area ratio - a combined acoustical and airflow performance-optimisation metric. This is calculated from conventional standardized metrics, takes a value of unity for a simple opening, and increases with increasing overall ventilator performance. Theory describing the open area ratio for ventilator characterization, and its limitations, are reviewed. Finally, to illustrate its benefits and capabilities, the proposed method is applied to the analysis of existing ventilator experimental results.