B.T.H. "Rice Kellog" 12-inch permanent-magnet moving-coil loudspeaker, 1931 B.T.H. "Rice Kellog" 12-inch permanent-magnet moving-coil loudspeaker
Marconiphone Type 90 moving-coil loudspeaker unit (mains model), 1930 Marconiphone Type 90 moving-coil loudspeaker unit (mains model)