Microlab Solo 1 Mk3 is not adjustable bass!

There are a couple of acoustic systems: Microlab Solo 1 Mk3 and Microlab Solo 2C they are connected via a splitter. So, in solo 1, the bass does not want to be regulated at all, it is just the same for both min and max adjustment. Solo 1 tried to connect separately, the same thing. What could be the problem?