I have an open plan type 1st floor, half of which is my listening area (family room.) The echo from the adjacent kitchen area was a problem. There is a half wall separating the two areas, plus a 4' walk thru.
I built 2" thick wood doors filled with 2" FG. The walk thru area is closed with a full size door, 50"x108" hinged to and painted to match the wall that it folds against when open. The opening over the half wall was closed with a 6 panel folding wall, 126x72" when closed, using a hardware kit from Johnson Hardware. Gaps are about 1/8" with a few larger holes that I might fill in, but it works well, and opens and closes easily, making a convertible listening room. It blocks the midrange echo completely, along with appliance noise. It was a big project but well worth it.
Another 72x96" opening at the rear of the listening area will get the same treatment eventually.