Many photos abound of the Beatles in Studio 2 with the acoustic screens in the background. The screens are made of metal and painted white. They're hinged to both of the side walls at the far end of the studio, which is where the Beatles predominantly positioned themselves when they recorded.
The hinges allow them to be opened out so that they can create partitions within the studio. Partitioning the studio stops sound from leaking from one microphone to the other (for example, Ringo might have been behind the acoustic screens to stop his drums from leaking onto George's guitar track).
The screens are huge and were folded back to the walls during my visit.
Here they are in use: