Crown CM-200A, CM-310A, CM-700, GLM-100, LM-201 Application Manual

© 2000 Crown International, All rights reserved.
PZM® , PCC®, SASS® and DIFFEROID®, are registered trademarks of
Crown International, Inc. Also exported as Amcron

131374-1

®

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Crown International, Inc
P.O. Box 1000, Elkhart, Indiana 46515-1000
[phone] Fax [phone]
www.crownaudio.com

MICROPHONE TECHNIQUES FOR VIDEO

No matter what your video application — sports,
news, corporate training — the soundtrack quality
depends on the microphones you choose and where
you place them. This booklet covers microphone
techniques to help you achieve better audio for
your video productions.

There are many types of microphones, each de­signed to help you solve a specific audio problem.
We’ll sort out these types and tell where each one is
useful. Then we’ll cover specific applications — how
to use microphones effectively in various
situations.

TRANSDUCER TYPES

A microphone is a transducer, a device that con­verts energy from one form into another. Specifi­cally, a microphone converts acoustical energy
(sound) into electrical energy (the signal).

A ribbon microphone works the same, except that
the diaphragm is also the conductor. It is a thin metal
foil or ribbon suspended in a magnetic field.

In a condenser microphone (Figure 2), a diaphragm
and an adjacent metallic disk (backplate) are
charged to form two plates of a capacitor. Sound
waves striking the diaphragm vary the spacing be­tween the plates; this varies the capacitance and
generates an electrical signal similar to the incom­ing sound wave.

Fig. 2 – A condenser microphone.

Microphones differ in the way they convert sound
to electricity. Three popular transducer types are dy­namic, ribbon, and condenser.

In a dynamic microphone (Figure 1), a coil of wire
attached to a diaphragm is suspended in a mag­netic field. When sound waves vibrate the dia­phragm, the coil vibrates in the magnetic field and
generates an electrical signal similar to the incom­ing sound wave.

Fig. 1 – A dynamic microphone.

The diaphragm and backplate can be charged ei­ther by an externally applied voltage or by a perma­nently charged electret material in the diaphragm
or on the backplate.

Because of its lower diaphragm mass and higher
damping, a condenser microphone responds faster
than a dynamic microphone to rapidly changing
sound waves (transients).

Dynamic microphones offer good sound quality, are
especially rugged, and require no power supply.
Condenser microphones require a power supply to
operate internal electronics, but generally provide
a clear, detailed sound quality with a wider,
smoother response than dynamics.

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Currently, all Crown microphones are the electret
condenser type — a design of proven reliability and
studio quality.

POLAR PATTERNS

Microphones also differ in the way they respond to
sounds coming from different directions. The sen­sitivity of a microphone might be different for
sounds arriving from different angles. A plot of mi­crophone sensitivity verses the angle of sound in­cidence is called its polar pattern. Several polar
patterns are shown in Figure 3.

Fig. 3 – Polar patterns.

Three types of unidirectional patterns are the car­dioid, supercardioid, and hypercardioid pattern. The
cardioid pattern has a broad pickup area in front of
the microphone. Sounds approaching the side of
the mic are rejected by 6 dB; sounds from the rear
(180 degrees off-axis) are rejected 20 to 30 dB. The
supercardioid rejects side sounds by 8.7 dB, and
rejects sound best at two “nulls” behind the micro­phone, 125 degrees off-axis.

The hypercardioid pattern is the narrowest pattern
of the three (12 dB down at the sides), and rejects
sound best at two nulls 110 degrees off-axis. This
pattern has the best rejection of room acoustics,
and provides the most gain-before-feedback from
the main sound reinforcement speakers.

Choose an omnidirectional mic when you need:

All-around pickup

Best pickup of room acoustics (ambience or
reverb)

An omnidirectional (omni) microphone is equally
sensitive to sounds coming from all directions. A
unidirectional microphone is most sensitive to
sounds coming from one direction — in front of
the microphone. A bidirectional (figure-eight)
microphone is most sensitive in two directions:
front and rear.

An omni microphone is also called a pressure mi-
crophone; a uni- or bi-directional microphone is
also called a pressure-gradient microphone.

Extended low-frequency response

Low handling noise

Low wind noise

No up-close bass boost

Choose a unidirectional mic when you need:

Selective pickup

Rejection of sounds behind the microphone

Rejection of room acoustics and leakage

More gain-before-feedback

Up-close bass boost

An omnidirectional boundary microphone (such as
a PZM) has a half-omni or hemispherical polar pat­tern. A unidirectional boundary microphone (such
as a PCC-160 or PCC-170) has a half-supercardioid
polar pattern. The boundary mounting increases the
directionality of the microphone, thus reducing
pickup of room acoustics.

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Most unidirectional mics have proximity effect, a
rise in the bass when used up close. Figure 4 is a
frequency-response graph that illustrates proxim­ity effect. When the microphone is 2 feet from the
sound source, its low-frequency response rolls off.
But when the microphone is 2 inches from the sound
source, its low-frequency response rises, giving a
warm, bassy effect.

Fig. 4 – Proximity effect.

A special type of unidirectional microphone is the
variable-D type. Compared to a standard single-D
directional microphone, the variable-D has almost
no proximity effect, so it sounds natural when used
close up. The variable-D type also has less handling
noise and pop.

The most highly directional pattern is that of the
shotgun or line microphone (Figure 5). The shot­gun microphone is used mainly for distant miking
(say, for dialog pickup where you want the mic to
be off-camera). It is highly directional at high
frequencies and hyper-cardioid at low frequencies.
The longer the shotgun mic is, the more directional
it is at mid-to-low frequencies.

Fig. 5 – Shotgun microphone and its polar pattern.

FREQUENCY RESPONSE

Each microphone has a different frequency re­sponse, which indicates the tonal characteristics
of the microphone: neutral, bright, bassy, thin, and
so on. Figure 6 shows two types of frequency re­sponse: bright (contoured) and flat. A bright fre­quency response has an emphasized or rising high­frequency response, which adds clarity, brilliance,
and articulation. A flat frequency response sounds
natural.

Fig. 6 – Frequency response.

FORMS OF MICROPHONES

Microphones come in many shapes that have dif­ferent functions:

Fig. 7 – Handheld microphone.

Handheld (Figure 7). Used in the hand or on a mic
stand. An example is the Crown CM-200A cardioid
condenser microphone.

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Fig. 8 – Lavalier microphone.

Lavalier (Figure 8). A miniature microphone which
you clip onto the clothing of the person speaking.
Two examples are the Crown GLM-100 (omni) and
GLM-200 (hypercardioid).

Fig. 9 – Boundary microphone.

Fig. 10 – Unidirectional boundary microphone.

The PCC (Figure 10) is a unidirectional boundary
microphone. When you place it on a surface, it has
a half-supercardioid polar pattern. The rugged PCC­160 is especially useful for stage-floor pickup of
drama and musicals; the PCC-170 has a sleeker look
for miking a group discussion at a conference table.

Fig. 11 – Lectern microphone

Boundary (Figure 9). Boundary microphones are
meant to be used on large surfaces such as stage
floors, piano lids, hard-surfaced panels, or walls.
Boundary mics are specially designed to prevent
phase interference between direct and relected
sound waves, and have no off-axis coloration. Free-
field microphones are meant to be used away from
surfaces, say for up-close miking.

Crown Pressure Zone Microphones® (PZMs®) and
Phase Coherent Cardioids® (PCCs®) are boundary
microphones; Crown GLMs, CMs, and
LMs are free-field microphones.

Lectern A lectern microphone (Figure 11) is de­signed to mount on a lectern or pulpit. For example,
the Crown LM-300A and LM-300AL are slim, el­egant units that plug into an XLR connector in the
lectern. The LM-301A screws onto a mic stand or
desk stand. Each has a silent-operating gooseneck.
The Crown LM-201 mounts permanently on the lec­tern, and has a rugged ball-and-socket swivel that
adjusts without any creaking.

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