In this case too, we'd use the RT60 factor we described previously to measure the reverberation time. Due to the environment's dimension and the sound source having a higher volume (orchestras, amplified music bands), reverb tends to be very present indeed.
The hall's structure itself as well as its covering, have an essential role in defining the environment's acoustics. The principles we mentioned when we looked at tight environments using absorbing and reflecting materials (the showy draperies hanging in 18th century halls are absolutely essential for acoustics) to diffuse sound, are also applicable in this case. The absorption on behalf of spectators is a separate matter.