Subwoofer size proportional to room size
Some small subwoofers (cone diameters) can play lower than larger ones. The thing is that small subwoofers can work well in small rooms. When you put small subwoofers in large rooms, they can’t move enough air to get sufficient SPL and they tend to bottom out when the sound source is most demanding, unless they have good built-in limiters but when limiters kick in that affects sound quality in other ways.
Larger speakers are needed for larger rooms and in general it is easier for the better designers to get better low extension out of larger subwoofers. I think you can see this most clearly in the Velodyne speaker product line but also in other product lines as well. In smaller rooms, bigger speakers can be turned down, but I can imagine there could be an overkill situation there too where the room is pressurized to an uncomfortable point or the subwoofers are sized to the point they take up too much space of a small room.
I would suggest overall that the subwoofer(s) should be proportional to the room size. The other speakers should also be sized proportional to the room size as smaller cube or spherical speakers may not have enough SPL capability to fill a large room without straining or distortion.
Just my observations from experience.
