Ribbon microphone

A ribbon microphone, also known as a ribbon velocity microphone, is a type of microphone that uses a thin aluminum, duraluminum or nanofilm of electrically conductive ribbon placed between the poles of a magnet to produce a voltage by electromagnetic induction. Ribbon microphones are typically bidirectional, meaning that they pick up sounds equally well from either side of the microphone.

In a moving-coil 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 light metal ribbon is suspended between the poles of a magnet. As the ribbon vibrates, a voltage is induced at right angles to both the ribbon velocity and magnetic field direction and is picked off by contacts at the ends of the ribbon. Ribbon microphones are also called "velocity microphones" because the induced voltage is proportional to the velocity of the ribbon and thus of the air particles in the sound wave, unlike in some other microphones where the voltage is proportional to the displacement of the diaphragm and the air.

The advantage of the ribbon microphone when introduced was that the light ribbon had a much higher natural resonant frequency than diaphragms in existing microphones, above hearing range, so it had flatter response at high frequencies. 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 were once delicate and expensive, but modern materials make certain present-day ribbon microphones very durable, and so they may be used for loud rock music and stage work. 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 pick-up pattern, ribbon microphones are often used in pairs to produce the Blumlein Pair recording array. In addition to the standard bidirectional pick-up pattern, ribbon microphones can also be configured to have cardioid, hypercardioid, omnidirectional, and variable polar patterns, although these configurations are much less common.

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