Here is a patent for a typical talk-back system in which these could be used.
US1416724 1922 1918 Kuhn AT&T--Telephone Circuits
Nice! Never saw the associated equipment since that was long gone along with the associated local test desks, which were centralized by the time I was on the scene. Note the lack of amplification in the transmit direction, only "4" in the receive direction.
In most older COs equipment frames were 11'6" with cable racks above that and a few more feet to the ceiling. Switch rooms had rolling ladders in each aisle supported by a ceiling track. Frame rooms often had a "mezzanine" or "cat walk" at about 6-7' above the floor so that lower and upper parts of the MDF could be accessed without using ladders at least along the walls. I have some photos I took of a mezzanine frame with these speakers hanging here and there. They're on a drive which is off line at the moment.