Round-robin testing determined that a high degree of reproducibility exists between laboratories that conduct sound absorption measurements in accordance with ASTM C423. Factors that include room dimension, source location and diffuser type have been identified as sources for differences in measurement results. Such lab to lab testing variation presents a challenge when reverberation chambers are replaced with new design and construction features that are not identical. An iterative process is required to produce measurements that match historical results. The presentation will describe the design approach utilized to construct a new reverberation room with different dimensions, diffuser types and materials. Experimental data will be presented showing the results of modifications made to the chamber after achieving initial qualification metrics. The iterative process provided an opportunity to study the impact of diffuser type and surface area and other properties on reducing the performance gap between the two reverberation rooms.