There is three schools on comparing subs but all involve placing the subs in the same spot or right beside each other. One thought is to run them flat as is with the same material and walk around the room to develop impressions. The second way is to sit in the same spot always and equalize both to avoid inconsistencies such as using a parametric equalizer on one and not the other. The third way is to use whatever tools come with the sub such as a single shot equalizer, trim controls, variable phase etc. Most of the time these three approaches yield the same impressions but not always.
