finally the flutter echo disappeared!
very strange ...
when i had the traps temporary placed to the wall there was too much.
after i mount them with screws and made them steady it magically disappeared
now i have some only
at the end of the room so i may make one more trap pair in the future
here are the last 3 picts
1. i find a soft tape and place to the back side of the traps (to avoid clack [is this the right word?])
2. i hit hit a voltage line (the white hole). thank god im alive ... just burn a fuse.
3. the end (to the black border is the only place with echo)
thanks very much everybody for posting here! appreciated
edit: also moved to ~42%