"To user above who uses ARC do you still get diffusion boards and carpets and etc?" The better the room acoustics, the less the correction needed. To me(my opinion); ARC shouldn’t be used to grind away major room/system problems. Just a way to polish what remains, after any big issues are addressed.
Is Auto Room Correction Right For You? Well, Here You Go...
...covers the fundamental problems rather well...
Part 1:
https://www.youtube.com/watch?v=LcGFpYJNE7A
And Part 2:
https://www.youtube.com/watch?v=aRJJ8XJAT54
Part 1:
https://www.youtube.com/watch?v=LcGFpYJNE7A
And Part 2:
https://www.youtube.com/watch?v=aRJJ8XJAT54