Our Microphone of the Month is the RCA KU2a, which was one of the earliest unidirectional ribbon microphone.

The KU2a is often known as the ‘Skunk’, because of the distinctive white stripe along the rear of the microphone grill. Marking the rear of the mic may seem a little counterintuitive, but this gave the boom-operator a clear indication of where to point the microphone, aligning the stripe with the actors or other sound source.

Unidirectional microphones were a real challenge for the early film industry because the common transducers of the day were generally bi-directional ribbons, or omnidirectional carbon or dynamics.

In the KU2a, directionality is achieved in a cunning manner. The ribbon is divided into two, with the top half acting as a normal figure-8 ribbon microphone. The lower half is sealed at the rear and is connected to an acoustic chamber, which makes the ribbon behave as a pressure transducer, with omnidirectional characteristics. These elements combine together to give a cardioid directional pattern.