These were great rooms. Quite large...maybe 20' x 20'.

 The string room's interior was an acoustical tile of some sort to give the room brilliance.

The horn room's interior was burlap covered insulation which
gave the horns a nice sound.

Generally, from what I remember, it was rare when both rooms would be used simultaneously.

The rule in most R&B sessions was horns and strings were done separately.

In fact if it was only a string session, that would be done on the studio floor. The extremely high ceiling made for good string sounds.

The floor space that shows in this photograph accounts for approximately 25% of the available studio floor space, so you can get some idea how large the main room was.

Notes thanks to Ralph Terrana