Was just looking into phase aligning subs, but I found you probably also need to add delay to the closer speakers to compensate for the distance of the sound sources .88 ms per foot. as is pointed out in this thread https://gearspace.com/board/high-end/1276396-phase-align-2-subs-then-subs-main.html In the case of putting a sub under my desk most of the pressure first goes to my backwall to then reflect back, I could even pick up more when it then reflects off my front wall which is untreated at this spot and which adds more distance, maybe this is why my sub bass sounds less direct from my sub under the desk versus directly from my monitors.