Is this with, or without, Trueplay, Night Mode, or Speech Enhancement settings enabled/disabled - you didn’t mention your EQ, Sub-level settings either, or the type of audio source/codec?

Did you retune the room after adding the Sub?

Perhaps irrelevant, but just for clarification, is it the older/larger Sonos Sub, or the new Sub Mini?

Is the PlayBar wall-mounted, or not? Sorry but your post wasn’t clear to me. If so, is it set above, or below the TV - a photo might also assist here (perhaps) for users in the community here to maybe make some suggestions to try.

Hi. 
 

yes i have done all things supposed to do. Trueplay and adjusting EQ and SUB-levels. 
 

in one position bass sounds pretty good. But in all others same or worse. 
 

i have my playbar under TV and subwoofer in left front corner

i eill try to change position of the sub today  but corner normally gives best boost to bass  but i get many dips in the room :(

I always go for placing a Sub in a corner of the room too, out in front of my listening position is my choice, so I think you maybe okay where it is but definitely try other positions too.

Maybe it’s the Trueplay tuning that’s reducing the Bass on the Playbar due to the reflective surfaces in the room - have you tried it with Trueplay switched off to see if that may improve things?

I moved the Sub to the opposite corner behind the sofa and removed it from my system and started all over again and did a new Trueplay and a 180 degree setting. Now it is much better actually. Still i am missing some midbass from playbar. I would like to be able to set those manually. Don’t know why Sonos wont allow you to do that? All normal home cinema systems let you set the crossover freq manually ‍♂️