As Sean said you want to avaid piling up axial modes and use room dimensions that achieve as uniform of a distribution as is possible. There are a number of recommended proportions by various authorities that have been found to be favorable for Height/Width/Length:
Boner:H 1: W 1.26 :L 1.59
Sepmeyer: H 1: W 1.28 : L 1.54
Louden H 1 : W 1.4 : L 1.9
Volkmann H 1 : W 1.5 : L 2.5
Play with those proportions using your dimensions.
They are all fully discussed in the Master Handbook of Acoustics by F. Alton Everest, pgs 275-280. There are many other issues too and the Everest book is worthwhile for general theory and only a few bucks. It is very readable.
Sincerely
I remain
Boner:H 1: W 1.26 :L 1.59
Sepmeyer: H 1: W 1.28 : L 1.54
Louden H 1 : W 1.4 : L 1.9
Volkmann H 1 : W 1.5 : L 2.5
Play with those proportions using your dimensions.
They are all fully discussed in the Master Handbook of Acoustics by F. Alton Everest, pgs 275-280. There are many other issues too and the Everest book is worthwhile for general theory and only a few bucks. It is very readable.
Sincerely
I remain