Ribbon Mics

History

Ribbon microphones, sometimes called velocity microphones, were invented in the early 1920's by German physicist Walter Schottky and inventor Erwin Gerlach. They were first commercialized in the 1930's by RCA with the introduction of their Photophone Type PB-31. This had a big impact on audio recording and broadcasting. And RCA soon followed with the RCA 44A and then the 77DX (see below).

One reason for the immediate success of the ribbon microphone was that it possesses a very good frequency response (100 to 10,000Hz) that was superior to other microphones used at the time. In particular, the resonant frequency of the microphone was below that of human hearing (<40Hz), which is one of the factors contributing to the silky smooth sound of a ribbon microphone.

Note:

At the time, condenser mics had not yet achieved the technical level that we know today. The condenser mics in the 1930's tended to sound a bit harsh and brittle.

Note:

An interesting side note is that ribbon mics, although always popular with some recording engineers, are gaining in popularity because they sound good in the digital realm. The crisp high frequency response of digital recording can be a bit much, in certain contexts, with condenser mics. But, the natural high frequency roll-off of ribbon mics can keep the highs from being over-hyped.

Technology

Ribbon microphones, are broadly included with dynamic microphones, but, in reality, they work in a completely different way. In the ribbon microphone, a thin ribbon of metal (usually aluminum), is placed between two powerful magnets. A voltage is generated when the ribbon is moved by sound. This voltage corresponds to the audio and is at a very low level. This is why ribbon mics require preamps with a very high gain, compared to dynamic mics, and especially condenser mics.

Note:

Because the output of the ribbon element is so low, ribbon mics traditionally have an output transformer which boosts the signal a bit. Even so, ribbon mics generally need a preamp with lots of gain (as much as 70dB!). However, some newer designs use active circuitry to amplify the signal, and thus have outputs similar to other mics.

Ribbon mics have a figure eight polar pattern which is a natural consequence of their design. The aluminum ribbon, which is the mics single moving part, is exposed at the front and the back. This allows for sound pickup from the front or the back while rejecting the sides.

Note:

It is possible to make ribbon microphones that have a cardioid pickup pattern. However, the additional circuitry, and sometimes a second ribbon, plus case baffling, can compromise the sound.

Examples:

The early days of radio and recording were dominated by ribbon mics such as the RCA 77A, 77B, 44A, 44B. These RCA mics are collectors items, and their sound is cherished among those who appreciate the ribbon mic sound. Thousands of mellow old recordings owe their sound to being captured with ribbon microphones.

In current times, Royer has dominated with their R121 and R122 mics. These mics have become studio "go-to" mics when desiring the ribbon mic sound, often described as "mellow and smooth".

Note:

The figure-eight polar pattern of ribbon mics is inherent in the design of the mic itself, so naturally the mic lends itself to situations where it is advantageous to pick up the sound in this way, such as Blumlien Stereo recording (requires two figure-eight mics).

Attention:

Normal, passive, ribbon mics should never be used with phantom power. The presence of phantom power can destroy the mic! This does not apply to active ribbon mics which have circuitry that requires phantom power. Please check the technical specifications of your ribbon mic, or contact the manufacturer, to determine if it is safe to use phantom power.