STC (Standard Telephones and Cables) model 4033-A microphone, 1940-1965.

This cardioid composite microphone was produced for the television age. A more directional microphone was required, that would pick up the sound of the action in front of the camera, without the sound of the camera mechanism behind. The area around a microphone from which it can pick up sound is called the polar pattern. By combining the moving coil from the STC 4035 microphone with a ribbon, a cardioid, or heart-shaped, polar pattern can be achieved, which picks up lots of sound from in front, but little from behind the microphone. Thus, the 4033-A was born. This microphone was frequently used as a boom mic for TV production, as well as for outside radio broadcasts, where it was useful for cutting out unwanted background sounds. It has the added advantage of being able to switch between the ribbon and moving coil, or both, to give different polar patterns in different circumstances.