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Unidirectional Ribbon Microphone
By Sam Inglis


Inspired by RCA's BK5, AEA's latest mic combines classic ribbon tone with a supercardioid polar pattern.

Nowadays, ribbon mics are often perceived as specialist tools for miking things like guitar amps, drum kits and brass instruments, but in their heyday, they served all sorts of applications. Ribbons were used for Foley capture, stage vocals, radio DJ miking, and there were even ribbon lavalier mics for TV interviews.

In many of these roles, the ribbon mic's native figure-8 polar pattern was more of a hindrance than a help, and manufacturers used all sorts of ingenious tricks to try to create a ribbon mic with a 'unidirectional' (cardioid) pickup. Mics such as the Western Electric/Altec 'birdcage' and STC 4033 tackled this challenge by combining a figure-8 ribbon element with an omnidirectional moving-coil capsule, while RCA's chief designer Harry F Olson did so using acoustic means.

The most famous of RCA's unidirectional ribbon mics are probably the iconic 77, with its mechanically switchable patterns, and the rare KU3A 'skunk mic', one of the best ribbon mics ever made. However, there's another, less well–known RCA design that now attracts a cult following. Said to have been designed, among other things, for recording gunshots for movie soundtracks, the BK5 was notable both for its somewhat cardioid pickup pattern and its ruggedness. On neither front does it score highly against today's mics, but what the BK5 does have is a very characteristic mid-forward sound. (Indeed, we often assume today that ribbon mics are universally dark and smooth, but unidirectional models all tend to be brighter and more mid-rangey.)

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Published January 2020