It is to be expected that variations in the field will account for drop in performance from those measured in a laboratory, significantly worse performance can typically be traced to a failure to follow three simple checks.
A relatively inexpensive hobby of mine is the collecting of old technology books. My collection includes books on rebuilding player pianos, blacksmithing and a mail order course on how to set up a vacuum tube radio repair shop (I will be set if my time machine leaves me stranded in the 1850s or 1950s).
Also called the “coincidence dip” or “critical frequency,” this hole-in-the-wall is the easiest way for noise to travel through most walls; a narrow band-pass at 3000 Hz. Today, a new hole-in-the-wall gang is taking advantage of this natural phenomenon.
Acoustics is given a low priority in many building projects. It usually doesn't start off that way at the beginning of the project but its high status can be slowly chipped away by noisy site selection, misprogramming of the building, cost-cutting measures here, nonprofessional opinions there and compromise (pronounced "surrender") by weary building committee members who just want the project to be done.