The history, usage and appeal of ribbon mics
As this issue of Premier Guitar focuses on recording, we’re going to examine a device
most of us rarely encounter (except on recordings and in movies), known as the ribbon
microphone. Rarely used at guitar gigs, the ribbon mic is de rigueur in recording studios
all over the world. We’ll examine the reasons why in a moment, but first…
Microphones were common enough since the advent of the telephone. These mics were carbon-granule type: sound vibrations would cause the granules to vary their conductivity, resulting in an electrical signal form of the sound. They were quite rugged, and even the first men in space and on the moon spoke though antiquated, but dependable, carbon mics. Unfortunately, they had poor frequency response, so they were eventually constrained to telephone use only until around 1970.
It wasn’t long before carbon mics had competition. Crystal mics actually used crystal, like a cigarette lighter. By using a mechanism to push on the crystal (or a ceramic mounted equivalent), electricity is generated. While crystal and ceramic microphones surpassed the old carbon types in performance, you and I would never use one on stage or in the studio. Their performance is still rather inadequate for quality recording (blues harp players excepted). Dynamic microphones are the de facto standard for most of us. They sound great, are relatively simple and cheap to manufacture, are rugged, and have easily controlled coverage patterns. A dynamic mic is like a loudspeaker in reverse. The key element in a dynamic mic is a diaphragm attached to a little coil, which usually fits into a magnet. When sound vibrates the diaphragm back and forth, a tiny voltage is generated, which is an analogue of the sound. Most dynamic mics sound pretty good, with the best units offering up excellent performance—especially for the money spent.
How many of you know the name Walter Schottky? Ol’ Walt is primarily known for his Schottky diodes but he, along with an unsung partner, Erwin Gerlach, also invented the ribbon microphone in the early 1920s. His designs are now used daily in the recording world, and his diode designs are even more plentiful in high-quality electronics. By the end of the twenties, RCA geared up to produce commercially viable ribbon mics. Many are still in use, sound fabulous and are quite collectible. How Do They Work? In a ribbon microphone, a very thin sheet of foil is suspended in a magnetic field—very thin, around one to two microns thick (.00005 inch). The ribbons are folded or corrugated anywhere from less than 12 to a little more than 24 corrugations per inch. While it’s possible to actually replace the ribbon element, I don’t recommend you try it—the ribbon will likely fall apart in your hands. Despite that admonition, you can actually improve the performance of a mediocre ribbon mic by replacing the diaphragm if you do it correctly.
The electrical signal generated by a ribbon is different from that of a dynamic mic, but technically speaking, a ribbon mic is a type of dynamic microphone—they both move back and forth in a magnetic field. Older ribbons differ from modern designs in significant ways. Older designs have very low output and very low impedance (0.2 Ohm in many cases). This impedance is so low that we need to bring it up to drive what we usually consider to be low impedance lines, so a transformer is used to increase both the signal and the impedance.
Transformers are tricky. In a guitar amp, one can hear the difference between an ordinary transformer and a boutique equivalent. The same applies to microphone transformers. If you lack the inclination to replace the ribbon element, a transformer upgrade can yield equally impressive results, but if distortion of a signal is to be kept as low as possible, a good transformer can be quite expensive. Fortunately, many of today’s designs have plenty of output—even more than moving-coil dynamic mics in some examples. In either case, a high-quality, low-noise microphone preamp can sound great. With the right preamp, you might be able to forgo the supplied transformer. Note that you might need 60dB of gain, so audition any preamp you buy not only for sound quality, but also for noise.
Condenser mics need a power supply. Ribbons do not. Older ribbon mics could be damaged by hooking one up through a preamp designed for condensers, so be careful. Many preamps allow a choice. Most ribbon mics have on-board transformers or preamps. The latter may need a phantom 48V power supply from your mixer, just like a condenser. Use care here: many ribbons will be damaged if hooked to a phantom power supply. Never hook up a ribbon mic to your mixer without checking. Newer designs are more likely to shrug off the mistake, but read the manual.
Speaking of shrugging off mistakes, another difference is durability. Some of the older—but really great-sounding—ribbon mics would fail from physical shock, but often stood up well to high SPLs. This can be tricky, too. A full symphony orchestra can play louder than my blues band usually does. A ribbon can certainly be used in high SPL environments, but be careful about a loud singer blasting away right into the mic without a pop shield. In fact, it’s good idea to always leave the pop shield on, especially when transporting or setting up the mics. Once set up, you might be able remove it, depending on the design, unless you’re recording a singer. Today’s ribbons are far more rugged. Even so, never scream or blow directly into any ribbon without a pro-quality shield. In fact, don’t blow into a ribbon mic, period.
What Are They For?
In a word: fidelity—accuracy in details, transient response, incredibly sweet and clear highs, clean mids and rich, accurate lows… probably the most natural presentation ever. Yet, they can be lush and romantic, with great warmth, and without bloat. Mic techniques coupled with the right electronics give you flexibility. Want a bit of bloat or extra warmth? Like their dynamic moving-coil brethren, ribbon mics suffer from proximity effect. Get really close, get lots of bottom. Place the mic a couple of feet away, clarity and balance start to return. Some models have a choke or high-pass circuit on board to attenuate low frequencies for close micing.
Can’t we get this level of performance with any decent mic? Nope! Here’s why: If you start with a non-linear transducer, be it loudspeaker, phono cartridge or microphone, it’s very difficult to linearize. If you start with a distorted transducer, it’s even worse. There are distortions present in all transducers—even if you think you can’t hear them. Since the electronics we’re feeding have distortion as well, the distortion is additive (actually, mathematically, it’s worse; with noise, for example, you add the squares). Many types of distortion are non-linear—they sound dissonant. If you distort the distortion coming from the mic (with electronics), you have audibly destructive fresh distortion components. If you think your chain is clean with a conventional microphone (and it might be!), with a good ribbon and transformer/ preamp, it won’t be just clean, it’ll be pristine. The ribbon microphone is the cleanest mic out there. The primary reason is the low mass of the diaphragm. Less inertia means an intrinsic ability to follow waveforms more accurately.
Figure-8 pattern typical of ribbon microphones
Cardioid (heart-like) microphone pattern
Some ribbon mics have long ribbons with a short acoustic path around the magnets, while others are the opposite. Pros select mics with these parameters in mind, but for many others purchase decisions are often dictated by pricing rather than coverage and pattern. In theory, a longer ribbon has more limited vertical pickup pattern—better for cleaner sound, as the reflective ceiling and floor surfaces contribute less coloration and reverb. There are applications, however, when you want the added ambiance.
Today’s ribbons can actually be used on stage. Combining a variable pattern with natural spectral balance and head-turning transient response can give you the very best of a good acoustic guitar—about a bazillion times better than a “quacky” onboard pickup. From oboes to piccolos, from violins to French horns, ribbons work great with acoustic instruments. No matter the music, ribbons rock.
Due to the large size of the “motor,” ribbon mics have been large from day one. Not all are large. Some look like regular hand-held, dynamic moving-coil mics, while some look like Johnny Carson’s. The old RCAs are dripping with vibe cosmetically and many companies emulate that look.
How Much Do They Cost?
In general, you get what you pay for. Many cheaper designs are based on established products—even those from Eastern Bloc countries where engineering has always been cherished. Not all of us require the performance of a $2000 mic yet have an appreciation for the strengths of a ribbon. Even imperfect designs still have a certain character that, in some applications, will be impressive compared to a PA-style microphone.
That said, there’s a commercial reason for the higher price of the better brands: they are great performers. There’s also a mechanical reason: better mics have tighter tolerances, leading to better performance and consistency from unit to unit. Furthermore, the actual physical construction has an effect of the performance of any microphone.
Aside from effective isolation from extraneous vibrations, the mic’s chassis and popshield must be optimized for low coloration. An improperly designed pop shield can behave like cupped hands, albeit to a lesser degree. The most sophisticated manufacturers have the facilities and procedures in place to design all aspects of the microphone for better performance in all areas, while low-end mics are sometimes knock-offs of existing designs—warts and all. As with hi-fi speakers, guitar amps, pickups, etc., there’s no substitute for listening. Finally, ribbons are prone to hum and noise, so try to get a money-back guarantee, and test the mic quickly after purchase.
As far as actual street pricing goes, imports like Nady and Samson have much to offer the amateur and semi-professional recordist. Brands like Royer, on the other hand, can be fairly expensive to really expensive. Some come with nifty shock mounts; some have cool wooden cases (don’t slam a ribbon’s case closed with the mic inside). If a 48V phantom power supply is specified, you can expect higher output and higher impedance: there’s circuitry on board. While most have a figure-8 pattern, some offer more coverage options, so read the specs.
At the entry-level, Nady offers a mic at under $200 and it ain’t bad! Sampson has a $400 model. Groove Tubes does more than tubes, as evidenced by their Velo line, with a couple of models between $650 and $1000. They call ‘em Velo because ribbon mics were originally called velocity mics. My favorite mic name has to be the Blue Woodpecker. Blue has lots of mics, and the Woodpecker sells for around a grand. The famed Beyerdynamic line is also a good value from $700 to around $1300.
At the higher end, companies like AEA ($900 to $3600) and Royer ($1300 to $4500), are the equivalent of Gibson, Martin or even D’Angelico guitars. It’s all a matter of your requirements and priorities. As the man said, (I’m paraphrasing) you can’t always get what you want, but you can get what you need.