That was then
The Altec 639A and 639B cardioid directional microphones were also sold under the Western Electric name, as shown in this ad from the October 1940 issue of Electronics magazine. The 639-type microphone combined a dynamic moving coil pressure element and a ribbon velocity actuated element enclosed in a housing that served as a protective guard and as a windscreen. The output of these two elements were used independently, or were combined in various proportions by means of a selector switch attached to the microphone to yield several directional patterns.
The 639A consisted of a ribbon velocity element and a dynamic pressure element, whose outputs are combined so that they yield a cardioid pattern. The 639B had a six-position switch that yielded omni, cardioid, several types of hypercardioid and figure-eight patterns.