On Ribbon Microphone diaphragms and their sonic signature, compared to others
By Cliff Henricksen
Many recording artists (including “engineers”) love using ribbon microphones, especially for recording voice and “acoustic” instruments.
Like a player’s experience with their instrument, the recording artist’s experience with their microphone (the experience of the person actually making the recording) is also unique, hard to explain and hard to translate to others. I’ve had extensive experience working on “tone” with, for example, electric guitar players, including some famous ones (no name-dropping here; so unattractive). As artists, they are so much deeper inside the tone they hear and so deeply involved in the mechanism of creating tone, that it’s impossible for an outsider (anyone outside the experience) to appreciate. To the artist, it’s as real and tangible as the art itself. I know this, and so I’ve learned to accept what they tell me as truth. The same is true for artists that use microphones in their work, to create a beautiful instrumental tone. Those deeply and intimately involved in the recording process hear and perceive things no one else does. It’s uniquely personal and a fact of the process. I mean, they have no reason to lie about this. It’s as honest and real as the art itself.
Lovers of ribbon microphones have their preferences for such devices for reasons only they know, or feel. Maybe they’re really not sure why either, preferences being the sum total of a vast assortment of different phenomena and signal-contributing elements that make the sound they are involved with.
I’ve wondered a lot about why we (and I) love the sound we get from ribbon diaphragms. Maybe it’s their basic nature that makes a sound we love. Think about the other kinds of transducers you can use:
The condenser microphone’s diaphragm is typically circular diaphragm stretched to a very high tension. It resonates (mechanically) way above the upper limit of hearing (supposedly 20KHz). It’s stiff as can be. Thus it has some kind of a musical character, like the subsonic character of a drum-head below its principle resonance. Condensers don’t move much and when they do, they get stiffer, like a drum-head. They have built-in amplification and tend to create "hot" output signals with pretty low noise. Condenser mics are used everywhere anyone does recording, a very popular and useful general category of microphones. Condensers are available with omnidirectional and unidirectional pickup patterns via all kinds of methods including dual-diaphragms and resonant/damped back-cavities.
The dynamic microphone is basically a loudspeaker in reverse, and early headphones were made by putting electrical power into dynamic microphones and putting them into small enclosures close to the ears (“the cans”). Dynamic mics have resonances in the bass region but because they are typically dome diaphragms with mechanical suspensions, made of paper, metal or some composite, they have mechanical resonances that occur all throughout the audio region. They are probably the most mechanically-complicated microphone, consisting of a diaphragm, suspension element, resonating back-cavities (for uni mics), a coil “former” (cylinder the voice coil is wound on), a pair of lead-outs, and so on. This is all vibrating when sound hits it and thus has its own musical character; harmonics that speak when the microphone speaks. Like a different tube of oil paint, dynamics all have different sonic signatures and are very useful in a wide variety of uses.
Ribbon microphone diaphragms (the good ones anyway) are typically long, narrow pieces of almost-impossibly-thin aluminum and are relatively loose and non-resonant. If you take a ribbon diaphragm out of the RM1 and let it loose in the air, it will slowly float about, almost buoyant. It is the loosest and floppiest of all microphone diaphragms. Some ribbons are corrugated and have resonances in the bass region. Some are loose and have no resonances at all. Ribbon mics are typically bidirectional, due to their basic nature. This is very useful in specific applications.
So what do we perceive from these, due to the basic nature of the diaphragm. Does their basic nature contribute to their musical signature? Are the sound of condensers “tight” and stiff in nature? Are dynamics resonant and their signals full of their own mechanically-resonant acoustical signatures? Do ribbons have the least emphasis on resonances? Certainly condensers are widely used in recording everything. We know we can get good (some great) vocal sounds from the good ones. Dynamic microphones are preferred for snare drum, electric guitar amps and even many vocal recordings. Is this because we like the harmonic content they add to the sound they pick up? Ribbons basically sit and vibrate and really don’t have much of a musical character of their own. Is this what we love about the sound they make?