Ribbon microphones are exceptional. The first ribbon microphone that became commercially available revolutionized the audio recording and broadcasting industries. In particular, history knows this microphone as RCA Photophone Type PB-31. Soon after it appeared, the BBC-Marconi Type A microphone came into being. These facts aside, the development of ribbon mics emanated from field coins and permanent magnets. And, to end this introduction, it’s worth mentioning that the ribbon microphone and the ribbon speaker emerged around the same time. In fact, the invention of the ribbon speaker was possible due to the turning of the ribbon circuit in the opposite direction.
Ribbon Microphones: the Physics
Ribbon microphones offer great sonic characteristics, good transient response and low self-noise. They are quite popular in recording studios because of their high-frequency response. However, they tend to be extremely fragile, so they are not as popular as a condenser or dynamic ones. They offer good frequency response and great sound quality, as well as low-handling noise. To explain their operation, the ribbon microphone generates an output signal that translates into a movement of the conductor in a magnetic field. As a result, the voltage is impacted. Ribbon microphones have a thin corrugated strip of aluminium foil located between the poles of a permanent magnet. Thus, the ribbon serves as a diaphragm.
More on the Ribbon
The output voltage of the ribbon diaphragm is quite small, so ribbon microphones have a transformer that boosts the signal voltage. They have a highly-inductive source impedance that is quite sensitive to loading. In addition, they tend to have a low input level. Despite this, the used should carefully install the passive input attenuators. Afterwards, s/he must be careful with its use, too.
Unlike dynamic and condenser microphones, ribbon microphones respond to the particle velocity of the atmosphere. Dynamic and condenser microphones tend to respond better to fluctuations of atmospheric pressure. This being said, pressure and velocity tend to be out of phase. Therefore, it seems impossible to phase the three types of microphones together.
