Crown GLM-100 User guide

CROWN MICROPHONE APPLICATION GUIDE:
SECURITY AND SURVEILLANCE
© 2001 Crown Audio, Inc. All rights reserved PZM®
is a registered trademark of Crown International.
Also exported as Amcron®
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Crown International
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CROWN MICROPHONE
APPLICATION GUIDE
SECURITY AND SURVEILLANCE
This guide offers tips on using Crown microphones
to safeguard areas such as warehouses, offices, park-
ing garages, and building entries. Using these micro-
phones, a security officer can detect break-ins or
other undesirable activities. We’ll also describe how
to pick up police interviews and psychiatric sessions.
First let’s look at Crown’s line of mics for security
applications. All the mics are very small, and are
designed NOT to look like microphones, so they are
nearly invisible. They provide clear pickup of
speech.
In all these microphones, the low frequencies below
the voice range are filtered out to reduce rumble from
trucks, machinery and air conditioning. At high fre-
quencies, the response is boosted to help articulation.
Because of their tailored response, the Crown secu-
rity mics pick up conversations or other desired
sounds with extra clarity.
Some of the models are Pressure Zone Microphones
(PZMs). They use a miniature mic capsule mounted
very near a sound-reflecting plate or boundary, in the
Pressure Zone. In this zone, direct sound from the
sound source combines in phase at all frequencies
with reflected sound off the boundary. The benefits
are many:
• 6 dB more sensitivity
• 6 dB less noise
• a wide smooth frequency response free of phase
interference
• excellent clarity and “reach”
• hemispherical (half-omni) pickup pattern
• consistent pickup anywhere around the micro-
phone.
Other models are Mini Boundary (MB) mics. They
use a miniature, unidirectional mic capsule mounted
very near a boundary. Because they are directional,
MB mics can pick up less room reverb than PZMs
do. The result is an even clearer sound.
Below are notes on each Crown microphone model:
PZM-10
This is a miniature PZM that looks like a light
switch. The mic has built-in electronics, which are in
an attachedtube. The tube mounts in a ceiling, panel,
wall or table. It comes with an XLR-type connector
and requires 12-48V phantom power.
PZM-11
Like the PZM-10, the PZM-11 resembles a light
switch. It mounts in a standard electrical outlet box.
The mic comes with a screw-terminal connector and
requires 12-48V phantom power.

The PZM-11LL is the same as the PZM-11, but has a
line-level output. This lets you record directly into a
VCR without a mic preamp. The PZM-11LL can be
powered in two ways: 24V AC or 12-24V DC. In
video security systems, 24V AC is usually available,
and this can be used to power the mic. The output
connector is screw terminals.
The PZM-11LLWR is the same as the PZM-11LL,
but is weather resistant.
MB-3
This is a miniature supercardioid mic with attached
electronics that mounts in a ceiling panel, wall or
table. The mic comes with an XLR-type connector
and requires 12-48V phantom power.
GLM-100
This mini omnidirectional mic is easy to install tem-
porarily. Just tape it to any convenient surface. The
mic has an XLR-type output and runs off phantom
power.
The GLM-100/E is the same, but can be connected
directly to a wireless transmitter. At the end of the
mic cable, you solder on a connector that mates with
your transmitter.
APPLICATIONS
Large rooms (warehouses, parking
garages, offices, etc.)
One way to cover a large room is with PZMs on the
ceiling (Fig. 1).
Figure 1
How far apart should the mics be to get uniform cov-
erage? Use the 2-to-1 rule. The spacing between
mics should be two times the distance from mouth to
ceiling. For example, if the ceiling is 5 feet above the
talkers’ mouths, the mics should be 10 feet apart.
Then the mics will pick up everyone about equally.
In general, use as few mics as possible that will do
the job.
If several mics are on at the same time, the recorded
sound might be reverberant or muddy. It helps to run
all the mics into a gated mixer (automatic mixer),
which turns on only one mic at a time – the one near-
est the person speaking. This keeps the sound clear.
If the ceiling is very high, mount the PZM-11 or
PZM-11LL on support posts and/or walls, about 10
feet off the floor (out of reach).

Medium size room (small office,
group therapy room, home, etc.)
Here you have a choice of PZM mics or the MB-3
mic. The PZMs are omnidirectional; the MB-3 is
unidirectional.
If the mic must be mounted in the ceiling near a wall,
and most talkers are in the middle of the room, the
MB-3 is a better choice (Fig. 2). It will pick up less
room reverberation than the PZM would in the same
location.
Figure 2
If the mic can be mounted in the ceiling near the mid-
dle of the room, and most talkers are in the middle of
the room, the PZM is the better choice (Fig. 3). It
will pick up less roomreverb than the MB-3would in
the same location.
Figure 3
Since the MB-3 is unidirectional, why doesn’t it pick
up less reverb than the omnidirectional PZM? If the
MB-3 is overhead of the talkers, it picks them up
approximately 90 degrees off axis, where its output is
reduced by 9 dB. So it picks up talkers rather
weakly, but picks up reverb strongly on-axis.
The MB-3 works best when talkers are in front of the
mic and within its 60-degree pickup angle. For
example, when the mic is near a wall and the talkers
are in the middle of the room (Fig. 2).
Police interview room or psychia-
trist office
Mount a PZM-10, PZM-11, or PZM-11LL in the
ceiling directly over the interview table (Fig. 4).
Another placement is in a wall close to the table at
mouth height. Since the mic resembles a light
switch, it does not intimidate the interviewee.
. Figure 4
If possible, deaden the room acoustics by adding cur-
tains, carpet, or acoustic-tile ceiling. This reduces
room reverb and provides a clearer sound.

Subway station
Mount PZMs of your choice in posts, in the ceiling,
or in walls.
Mount the mics 10 feet above the floor, out of reach
(Fig. 5).
Figure 5
If the mics will be 10 feet from people on the aver-
age, mount the mics 20 feet apart to pick up everyone
about equally. That is, the mics should be no more
than twice as far apart as they are from the people.
Entry
Mount a PZM in an overhang, or mount an MB-3
aiming down over the entry (Fig. 6). It is best not to
expose the microphone to rainfall.
Figure 6
GLM-100 techniques
The GLM-100 miniature mic is easy to install and is
for temporary use. Simply tape it to a wall, ceiling,
or upper corner of a room.
If possible, place the GLM so it has a line of sight to
the person speaking. A mic behind a barrier or fabric
tends to sound muffled.
By following the suggestions in this guide, you
should be able to discreetly pick up speech and other
sounds with clarity.