If you’ve ever seen an old movie or TV show where there was a radio announcer, you’ve probably seen a ribbon microphone. The RCA 44 (see Edmund Lowe, on right) had exceptional sound quality and are still valued today in certain applications. The name ribbon microphone is because the sound pickup is literally a thin strip of aluminum or other conductive material.
Unlike other common microphones, ribbons pick up high frequencies much better due to the high resonant frequency of the metallic ribbon. This is not only better in general, but it means the ribbon mic has a flatter frequency response even at lower frequencies. Another unique feature is that the microphone is bidirectional, hearing sounds from the front or back equally well. It is possible to build them with other directional patterns, although you rarely see that in practice.
In the early 1920s, Walter Schottky and Erwin Gerlach developed the ribbon microphone (and, coincidentally, the first ribbon loudspeaker). Harry Olson at RCA developed a ribbon mic that used coils and permanent magnets which led to the RCA Photophone Type PB-31 in 1931. Because of their superior audio response, they were instant hits and Radio City Music Hall started using the PB-31 in 1932. A newer version appeared in 1933, the 44A, which reduced reverberation.
The BBC and Marconi also made similar microphones including the Type A and the Coles 4038. The Russian version was the Oktava. Although the technology is nearly one hundred years old, many sound engineers still use ribbons because of the fidelity of the recording.
Much of what motivated Olson was recording sound for movies. The sharp directional characteristics of the ribbon were helpful when recording for motion pictures. Noisy cameras could be hidden at the sides of the ribbon microphone, and would be mostly left out of the recording.
How it Works
The ribbon mic is actually just another form of dynamic microphone. A conventional dynamic mic uses a moving coil as a transducer. Of course, the sound has to move the coil, and there is a definite limit to how light you can make the coil.
In a ribbon mic, the ribbon acts as a transducer, of course. The microphone suspends the ribbon between the poles of a permanent magnet. As the ribbon vibrates, the motion and the magnetic field generate a voltage measured by two contacts, one at either end of the ribbon.
Proponents of the ribbon microphone claim that the mechanism is closer to how your ears work, which makes them sound better. The output voltage is generally low compared to a traditional dynamic microphone, necessitating a transformer. However, modern designs often use improved magnets and transformers that can meet or exceed the output voltage of a typical microphone.
About the only downside to the ribbon is it is relatively fragile. Loud instruments (like drums) can damage the ribbon. Even wind can stretch or tear ribbons. Most modern ribbon microphones can handle phantom power intended for dynamic mics, but some can take damage from power on the signal lines.
The video below shows the construction of a modern ribbon microphone.
Many singers and musicians appreciate working with ribbon microphones, even today. Everyone from Frank Sinatra (left) to Elvis Presley sang into them, and they are still popular with certain artists and recording engineers.
You can still buy ribbon microphones. In fact, inexpensive imports allow even budget-conscious audiophiles to record using a ribbon microphone. Companies like AEA, Royer Labs, Crowley & Tripp, and many others still make this type of microphone. Some use stronger materials for the ribbon or have different ways of securing it. Some have integrated amplifiers instead of, or in addition to, transformers. Some of those amplifiers even use tubes if you subscribe to the idea that tubes sound better.
A professional instrument can cost thousands of dollars, but others cost well under $100. Original RCA mics are still prized and usually quite expensive. A very serviceable mic should run you no more than $200.
If you want to hear a comparison of a dynamic, a condenser, and a ribbon microphone, check out the video below. You may or may not think the ribbon mics sound better, but you can certainly tell the difference between the three types with your ears.