I noticed when adding room treatments it is either "night and day" or barely noticeable.. A friend of mine treated his entire room, he didn't own a level or drill {he had 1 but it was a corded black and decker from the 80's and no key for the chuck, he did have a tape measure though lol...} so I brought some tools over and gave him a hand hanging his panels, I have listened to his system a bunch of times and I the changes must have been really subtle because I noticed nothing, he said the bass osunded a lot clearer, but to me it sounded the same... He spent around $1000 treating the room, I would want an audible difference, but he was happy... Other rooms I have been in sounded amazing after treatments, most of that was to correct blatant issues...