Five Classic RCA Ribbon Microphones
by Mike Dorrough, KO6NM, and Gary Halverson, WA9MZU
Considered by many as the most natural sounding microphone
every made, ribbon mics were immediately embraced by the
broadcast and recording industries. Not requiring any awkward
power supply or batteries in their operation, the first commerically
produced ribbon mircophones appeared in the early 1930's.
The ribbon microphone was also known as the velocity microphone
and was the last of the four basic microhone types developed,
following the dynamic, condensor, and carbon microphones.
The ribbons' natural sound can also be made to sound warm,
big, and syrupy (Bing Crosby-like) when placed within two or
three feet of the talent (generally, you can't close-talk a
ribbon without having a greatly exaggerated bass characteristic).
An adequate breath filter in front of the ribbon is also necessary
to protect the delicate ribbon (NEVER blow into a ribbon mic).
The output level of the ribbon is nearly always lower than
that of a dynamic microphone. For this reason, hum rejection
and shielding are important considerations in ribbon microphone
The active element is of course the ribbon, consisting of
a very thin corrugated aluminum ribbon clamped under light
tension and mounted between the poles of a strong magnet. The
extremely low impedance of the ribbon (tyically on the order
of 0.2 ohm) is fed directly into a step-up transformer to match
low impedance lines (50, 250, or 600 ohms).
Although other companies at the time were producing ribbon
microphones, RCA was top dog for several reasons. First, RCA
had the sales channels in place, with a pipeline into the broadcast
market. They also had huge advertising budgets. But perhaps
a more compelling reason was that the research and development
effort that went into these microphone produced a quality that
was unmatched by the competition. At the time, Western Electric
was the only other manufacturer that could successfully compete
with RCA, however, their only ribbon microphone was being targeted
into the motion picture industry.