Recording - February 2015 - 14

By Michael Schulze

Microphone technology has evolved a great deal over the last
century, and throughout that history there have emerged a handful of "go to" mics that have dominated particular periods and
genres. Many of your favorite modern bands are creating music
that harks back to specific historic periods, using some of the
same production techniques that were used by the greatest producers and engineers of all time.
Choosing the right vocal mic for your singer and your project
can create a sonic vibe that you can build your entire mix
around. In this article I will write about a few of the holy grail
vocal mics of popular music history, and how you
can emulate the sound of great old and new
recordings using currently available and affordable microphones. I'll reference some specific
recordings, but you can search for any of these
mics on YouTube and find many audio examples
and even shootouts with much less expensive
modern designs.
Most vocal tracks today are being cut with
large-diameter, dual-diaphragm condenser microphones. However, before I explain that mouthful,
let's take a look at an often ignored alternative: the ribbon dynamic mic. (We'll also take
a look at moving coil dynamic mics in a bit.)

Ribbon mics: a rich history
The first commercially available ribbon microphone was the RCA 44-A (shown in Figure 1),
introduced in 1931. A few years later the updated 44-BX quickly became the mic for vocals,
radio announcers, horns, and just about everything else due to its warm, smooth sound. To hear
this mic check out Frank Sinatra's The Voice of
Frank Sinatra. Many of the earliest Elvis Presley
recordings used this mic.
Ribbon mics contain a very thin strip of aluminum foil, only 2-3 microns thick (2-3 millionths
of a meter). The ribbon is corrugated to make it "springy"
so it can be stretched to a specific tension, which extends
the low end response by establishing a mechanical resonance at a specific frequency. The ribbon is suspended
within the field of a large magnet. (I can pick up small
screws with my Royer R-121!)
Sound pressure waves arriving at the front or back of the ribbon cause it to vibrate, and vibrating a piece of metal within
a magnetic field makes electrical current flow. Wires connect
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RECORDING February 2015

the two ends of the ribbon to a transformer to balance the signal
and increase the output impedance to about 300 Ohms, and that's
it. See Figure 2 for the inside (and outside) of the Royer R-121.
Remember, ribbon mics have a lower output than any other type of
mic, so expect to turn up the gain more than usual.
Pressure waves arriving from the sides push or pull the front and
back of the ribbon equally, so the ribbon doesn't move and no
sound comes out. This is why a traditionally designed ribbon mic
has a bidirectional ("figure-8") polar response, picking up sound
from the front and back, but not the sides. Later in the 1930s, RCA
introduced the pill shaped RCA 77-DX ribbon mic,
which combined omnidirectional and figure-8 ribbon elements to produce a cardioid, or unidirectional, polar response. The modern Beyer M160
uses the same principle. A single element ribbon
mic is a pure pressure gradient mic because it produces sound based on the difference in pressure
between the front and the back of the ribbon. Pure
pressure gradient elements exhibit the most extreme
proximity effect of any type of mic: you get more
low end response the closer you are to the mic.
While some modern designs like the Shure
KSM313 or Sandhill 6011A are fairly rugged,
most ribbons, especially vintage designs, are
incredibly fragile when hit with gusts of moving
air. That 3 micron ribbon can stretch out of
shape with the slightest puff of air, even if all
you're doing is walking while holding it! So never
blow into a ribbon mic or put it in front of the hole
on a kick drum (guitar amp cabinets should be
okay), cover it with the provided "sock" while moving it, and always use one or more pop filters
between the singer and the mic... or you'll be paying to have the mic's ribbon replaced. Oh, and
store the mic upright; older ribbons can sag under
their own weight even if you just set them down on
their side for a while.
To get the most out of a ribbon mic you must understand
three things. First, if you are using a figure-8 ribbon mic,
make sure there is no reflective surface behind the mic.
Back up away from studio windows and walls! However,
the rejection of sound from the sides provides much more
isolation than cardioids. I frequently record 3 or 4 horn
players standing shoulder to shoulder in a very small
room. I love to use figure-8 ribbons because there is little
leakage between the mics.

Recording - February 2015

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