Probably just need to adjust the volume in the controller. There could be a plethora of reasons, in general Sonos expects you to set volumes, and doesn’t make any effort to match volumes from grouped speakers (not even sure they could, since you’d have to say ‘I’m listening from this location’). 

Ok, thanks for the answer. Anorher questione: for me the speakers volume Is too high also when it's at the minum =1. Am I too sensitive?

THANKS!

There’s been many threads about that. Since Sonos uses digital amplifiers, there is of course a minimum volume that can be supported to push any signal, but I have no idea if Sonos is close to that at volume 1 or not.

For me, it’s not an issue, but if it were, I’d just move the speakers further away.

Some folks suggest adjusting the maximum possible volume in the controller allows a more fine control at lower levels. On the other hand, I have a set of PLAY:1s that flank my computer monitor for music playback, and I’ve never had an issue with volume level 1 intruding on any video calls. It’s unfortunately a personal issue, what works for me may not work for others.