This is going to be a very problematic room. 16' and 18' are very close together and 16 is almost the double of 7'8". All the modes are going to be similar and the summation of modes means many very large peaks. Given your choices, definitely C2 wtih sub.
Even using equalizer for C2/C1 to produce an even freq response, there will be prolonged decay time the problematic modes.
If it is not too late, change one dimension, maybe do 7'8", 13', 18'.
Even using equalizer for C2/C1 to produce an even freq response, there will be prolonged decay time the problematic modes.
If it is not too late, change one dimension, maybe do 7'8", 13', 18'.