The history of a ribbon microphone
The first mention of the ribbon microphones dates back to the early 1920s when Drs. Walter H. Schottky and Erwin Gerlach co-invented it. At the same time, they have invented the ribbon speaker by turning the ribbon circuit in the opposite direction. With a difference of a few years, Dr. Harry F. Olson of RCA started developing ribbon microphones using field coils and permanent magnets. The very first commercially designed ribbon microphone, which significantly impacted audio recording and broadcasting industries, was named RCA Photophone Type PB-31. Shortly after that one of the iconic ribbon microphones was produced by BBC and Marconi and named BBC-Marconi Type A.
How do they perform?
Ribbon devices are not nearly as common as a condenser or dynamic microphones, mainly because of their reputation for being fragile. However, they do provide good frequency response, excellent sound quality and low handling noise. Basically, the ribbon microphone produces an output signal in the same way as a dynamic microphone, meaning the conductor moves in a magnetic field inducing a voltage. Instead of a voice coil, ribbon microphone a thin corrugated strip of aluminum foil suspended between the poles of a permanent magnet. The ribbon, which may be as thin as 0.001 inches, acts like a ½-turn coil and also serves as a diaphragm.
The output voltage of the ribbon diaphragm is very small, and the impedance is very low. Therefore, the ribbon microphones include a transformer to boost the signal voltage. The highly inductive source impedance of ribbon microphones is sensitive to loading. The nominal (named) input impedance of a microphone preamp usually is 150 Ohm. The actual value should be 2000 Ohm or greater. Although seldom required because of the ribbon microphone`s low input level, passive input attenuators must be used with caution. Loading below 2000 Ohm will compromise frequency response.
Atmospheric particle velocity
A ribbon microphone responds to the particle velocity of the atmosphere. Dynamic and condenser microphones react to variations in atmospheric pressure. Pressure and velocity always are 90 degrees out of phase, and so it is not possible to phase ribbon microphones with condensers and dynamics.
Although more delicate than dynamic and condenser microphones, ribbons are finding new popularity in recording studios. Their silky high-frequency response delivers very accurate reproduction of instruments rich in harmonics such as strings or woodwinds. Vocals with excessive sibilance are less likely to exceed headroom limits of digital recording when using ribbon microphones. Ribbon microphones provide excellent sonic characteristics, good transient response, and low self-noise.
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