Welcome back to part two of our exploration of microphones. Last time out, we looked at
the different types of microphones:
dynamics, condensers, and ribbons.
We talked a little bit about how
each type works and what each type
is good for. (If you missed Part 1,
visit premierguitar.com/jan2011.
Take your time, we’ll wait.)
Now that everyone is on the
same page, let’s discuss a few
other important microphone
characteristics and how they affect
the sound the mic captures.
One of the chief characteristics
of a microphone is how it responds
to sound from a directional standpoint. Does it “hear” sound equally
well from all directions, or does it
respond more accurately from in
front of the microphone (that is, on
axis) than it does from the sides or
rear of the microphone (off axis)?
The response of the microphone
from all the different directions is
called its “polar pattern,” and there
are several different types.
An omnidirectional (or “omni”)
mic has a spherical polar pattern,
which allows it to respond to sound
coming from all directions. Omni
microphones also have a very even
frequency response compared to
mics with other polar patterns (all
other things being equal). This
makes them great as room mics.
Omni mics also work well for
recording delicate instruments and
instruments with a wide frequency
response that you want to capture
without emphasizing a particular
frequency. By carefully positioning
an omnidirectional microphone,
you can control the blend of the
source’s direct sound along with the
room’s ambient sound.
Because omnidirectional mics
are not, by definition, directional,
they don’t suffer from (or benefit
from, depending on who you ask)
an increase in bass frequencies
when they get closer to a source.
We’ve all heard the huge, bassy
voices of radio announcers who are
speaking with their mouth right
on the microphone. This is called
“proximity effect.” Because omni
mics don’t evidence a proximity
effect, you can place them very
close to a source without adding
excess low frequencies and, poten-
tially, low-frequency distortion.
The hypercardioid polar pattern for Shure’s SM57—the classic guitar-cab mic. The diagram on the left shows the pickup pattern for three frequencies: 125 Hz, 500 Hz, and 1000 Hz ( 1 kHz). At 0 degrees, the mic is
“hearing” virtually all the sound—this is the front of the mic. At all three
frequencies, sound is rejected from the sides ( 90 degrees) and rear ( 180
degrees), although the amount of rejection differs according to the frequency. Of these three frequencies, 500 Hz offers the maximum rejection
(at least - 20 dB) of sound coming from the rear. Notice how the 500 Hz
pattern creates a heart-shaped profile—hence the “cardioid” moniker.
Conversely, the 125 Hz pattern is circular, though not perfectly round.
The right diagram shows the mic’s pickup pattern at 2, 4, and 8 kHz,
respectively. Of these frequencies, the greatest rejection (nearly - 20 dB)
of rear sound occurs at 2 kHz. Images courtesy of Shure Incorporated
rejects sound from the sides. Figure- 8
mics are typically used in the studio,
and you won’t find them on too
many stages. They can be used to
capture a source along with some
room ambience or even to record
two facing sound sources simultaneously. Figure- 8 mics are also used for
specialized stereo mic’ing techniques
and for recording symphony orchestras and other large ensembles.
Some microphones allow you
to switch the polar pattern, which
certainly increases their flexibility.
However, perhaps 95 percent (or
even more) of the multi-pattern
microphones in use out there are
rarely, if ever, switched away from
the basic cardioid pattern. It’s nice to
have the option to switch between,
say, omni, cardioid, and figure 8,
but in practice, few of us ever do.
Another microphone character-
istic to be aware of is the maximum
SPL (sound pressure level) rating.
This is the volume at which the
microphone itself will start to
distort or even to suffer damage.
Dynamic mics can usually handle
high SPLs, which makes them great
in front of stacks, super-powered
amplifiers, and drums. on the other
hand, when subjected to massive
volume levels, a ribbon mic can
actually be damaged—the ribbon
can stretch or even break.
MITCH GALLAGHER is
the former editor in chief of
EQ magazine. He’s written
more than 1000 articles
and six books on recording
and music technology, and
has released an instruction-
al DVD on mastering. His upcoming book is
entitled Guitar Tone: Pursuing the Ultimate
Electric Guitar Sound. To learn more, visit
mitchgallagher.com.
