From Wikipedia, the free encyclopedia
The sensitivity pattern of a bidirectional
microphone (
red dot) viewed from above.
A ribbon microphone is a type of
dynamic microphone that uses a thin aluminum or
duralum ribbon placed between the poles of a magnet to
generate voltages by
electromagnetic induction. Ribbon microphones are typically
bidirectional, meaning they pick up sounds equally well from
either side of the microphone.
In the dynamic microphone, the
diaphragm is attached to a light movable coil that generates
a voltage as it moves back and forth between the poles of a
permanent magnet.
In ribbon microphones, a current is induced at right angles
to both the ribbon velocity and
magnetic field direction. As the sound wave causes the
ribbon to move, the induced current in the ribbon is
proportional to the particle velocity in the sound wave. The
voltage output of older ribbon microphones is typically quite
low compared to a dynamic moving coil microphone and a step-up
transformer is used to increase the voltage output and
increase the
output impedance. Modern ribbon microphones do not suffer
from this problem due to improved magnets and more efficient
transformers, and have output levels that can exceed typical
stage dynamic microphones.
Ribbon microphones have usually been delicate and expensive,
but modern materials make present-day ribbon microphones durable
enough for loud rock music and stage use. They are prized for
their ability to capture high-frequency detail, comparing very
favorably with
condenser microphones, which can often sound subjectively
"aggressive" or "brittle" in the high end of the frequency
spectrum. Due to their bidirectional pickup pattern, ribbon
microphones are often used in pairs to produce the
Blumlein Pair recording array. In addition to the standard
bidirectional pickup pattern, ribbon microphones can also be
configured to have
cardioid,
hypercardioid, omnidirectional, and variable
polar patterns.
One of the first ribbon microphones was the
RCA
PB-31. Produced in 1931, it was a breakthrough technology in
sound, and revolutionized the recording and broadcast industry,
setting a new standard in frequency response. The clarity and
realism were unmatched by any of the condenser microphones of
its day.
