RCA 77D

The RCA Type 77-D Polydirectional Microphone was introduced in 1945, and remained in the catalog for about ten years until it was replaced by the Type 77-DX which stayed in production until 1973.

Its beautiful streamline Art Deco style is so distinctive that it has become the universally recognised symbol of broadcasting and a de facto representation of a “microphone”.

Unusually for a ribbon mic the 77D is “polydirectional” which in modern parlance means multi-pattern. It uses a wonderful piece of design and engineering to achieve this.

Instead of being open on both sides like a conventional velocity microphone, the ribbon element in this microphone is coupled to an acoustic labyrinth, which forms the lower section of the microphone. The tube connecting the back of the ribbon to the labyrinth is slotted directly behind the ribbon. The labyrinth is stuffed with cow hair, and fitted with an adjustable shutter to secure various areas of opening. When the opening is completely closed, the microphone operates as a non-directional pressure (omni) microphone; at the wide-open position the microphone becomes bi-directional (figure of 8). With the proper size opening, the pattern becomes a cardioid by virtue of the phase shift which occurs.

You change the pattern with a screwdriver! You can also attenuate low frequencies with another screwdriver-operated switch on the bottom of the mic.

In reality the mic usually sounds best in its natural figure of 8 setting and that’s how it stays most of the time but the cardioid still sounds good and gets used occasionally on vocals when bleed is too uncontrollable and I can find my screwdriver. Likewise, the omni setting is useful for room sounds.

The 77D is a wonderful sounding microphone and considering the age of the design sounds remarkably high-fidelity. I love to use it on brass, on drums and if I’m recording old time or roots music I will use it on almost anything, it really does give any recording of a roots style of music a genuinely authentic sound.