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
around one to two
less than 12 to
a little more
than 24 corrugations
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.
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