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, potentially,
low-frequency distortion.
But because omni mics pick up
equally well from all directions, they
don’t isolate a source at all. That’s a
problem if you’re trying to record
several instruments at once and keep
them somewhat sonically isolated,
or use multiple mics on a drum kit
to control the level of individual
drums. Plus, for live use, omni mics
have no feedback rejection at all—
put one onstage with the monitors
turned up, and you’ll be faced with
screaming, out-of-control feedback.
A
cardioid mic has a heart-shaped
polar pattern. It picks up sound very
well in front of the mic, less well
from the sides (meaning the sound
from the sides will be colored and
reduced in level), and doesn’t really
pick up sound from behind at all.
This makes cardioids great for isolating
a source when recording multiple
instruments at the same time.
They’re also good onstage, as long as
you aim stage monitors or anything
that might cause feedback or bleed
at the rear of the mic, where the
sound rejection is best. Cardioid
mics have proximity effect, so when
they’re close to the source you’ll hear
a bass boost. You can use this to
your advantage to fatten up tracks
and to punch up the bottom end.
Hypercardioid and
supercardioid
mics have polar patterns that are
similar to cardioid, but have even
less response from the sides. Note,
however, that hypercardioids pick up
some sound from the rear. A hypercardioid
mic is great for a singer
who wants to use two stage monitors.
You can aim the two monitors
into the null points slightly off
center from the rear of the mic and
have good control over feedback.
A
figure-8 polar pattern works
pretty much as its name implies:
The mic picks up well in front and
also picks up well from behind, but
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 characteristic
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.
To help increase max SPL, some
microphones have a built-in “pad”
that reduces the effective level hitting
the mic, allowing it to handle
higher levels. For example, a mic
might be rated for 130 decibels,
then have a 10 dB pad that can
be switched in to increase the SPL
handling to 140 dB.
The tradeoff is that a mic
designed to handle extreme volume
levels may sacrifice sensitivity.
When a mic is built more
robustly, it typically can’t respond
as well to delicate signals.
That’s it for this month. Tune in
next time, when we’ll continue our
exploration of microphones.
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 instructional
DVD on mastering. His upcoming book is
entitled
Guitar Tone: Pursuing the Ultimate
Electric Guitar Sound. To learn more, visit
mitchgallagher.com.