Q: How do I make a good simulation of reverberation time in a large room?

A: First consider if the reverberation time is the best parameter to use. E.g. DL2 could be a better parameter for a larger room. Simulating reverberation time in a point response calculation in Odeon, corresponds to measuring the reverberation time. Therefore refer to a measuring standard e.g. ISO 3382. Make sure that you use only one Omni-directional source for each calculation job. In large rooms it is important to have sufficient distance between source and receivers, receivers should not be placed in the near field of the source but in the reverberant far field characterizing the room. ISO 3382-2 includes an equation describing the recommended minimum distance between source and receiver:
Where: V - is the Volume in cubic meters; C - is the speed of sound in meter/second and ^T - is the expected reverberation time in seconds.
Furthermore it is a good idea to use a larger number of source receiver pairs in large rooms than the measurements standard demands, to cover the larger area.
If the room consists of many coupled or unregular areas with different properties, it will may not be possible to find one reverberation time that characterizes the room and we advise you to supplement the reverberation time with analyses of STI, SPL, EDT, DL2 and auralisations in different areas.