New to the forum and have an interest in OB subs.
I have a room 23x22  8 ft ceiling and i am presently  using a single Velodyne ULD 15 sub and would like to move up to a 
OB sub . What combo of subs would give me equal or more bass output compared to my Velodyne.
2 GR 2 packs or 2 GR triples ? 
Would prefer the 2 doubles due to price and size .
MY main speakers are Magnepan Tympani 4A .
Todd