T
MB3
MINI-BOUNDARY
™
MICROPHONE
he AKG/Crown
®
MB3 is a miniature
boundary microphone for multi-miking
applications such as teleconferencing,
distance learning, boardrooms,
courtrooms, and security applications. This
low-profile, circular mic permanently installs
into a hole drilled in a table, lectern, or ceiling.
Thanks to its supercardioid pickup pattern, the
MB 3 greatly reduces ambient noise and
pickup of room reverberation. The result is a
clearer, more intelligible sound.
On the bottom of the mic is a tubular power
module with a 3-pin XLR-type output connec-
tor. It is powered by 12-48V phantom power,
and has a low-impedance balanced mic-level
output.
Features
• Small, inconspicuous.
• Installs permanently in table top, wall or
ceiling.
• Clean, clear, natural sound.
• Low-Z balanced mic-level output prevents
hum and high-frequency loss.
Specifications
Type:
Phase Coherent Cardioid.
Element:
Electret condenser.
Frequency response (typical):
50 Hz to 15,000 Hz at
30 degrees incidence to surface (see Fig. 1).
Polar pattern:
Half-supercardioid (supercardioid in
the hemisphere above the primary boundary).
See Figs. 2 and 3.
Impedance:
150 ohms, balanced (recommended
load impedance 1000 ohms or greater).
Fig. 1
+15
+10
+5
dB 0
–5
–10
–15
–20
–25
–30
Frequency Response
0˚
130˚
• Removable grille assembly can be painted.
How to Paint the Microphone
1. Using a small screwdriver, pry open one side
of the base, then the other side (Fig. 5).
Open-circuit sensitivity (typical):
22 mV/Pa* (
–33 dB re 1 volt/Pa).
Power sensitivity:
–30.5 dB re 1 mW/Pa*.
EIA rating:
–125 dBm.
Equivalent noise level (self-noise):
22 dB SPL
–35
20
100
1K
10K
Frequency in Hz
Fig. 2
Horizontal-Plane Polar Response
2. Remove the foam liner.
3. Wearing a dust mask, spray-paint the grille
assembly. Be sure grille holes are not clogged.
4. Allow to completely dry.
5. Make sure the LED is properly aligned.
6. Carefully place the grille assembly over the
base, and snap in place.
Installation
Tables:
In a table, typical placement for each
mic is an arm
’s length from the user. Install
one microphone in front of each person, or one
between every two people.
Lecterns:
If the microphone will be used on a
typical (0 dB=0.0002 dyne/cm
2
), A-weighted.
S/N ratio:
72 dB at 94 dB SPL.
Maximum SPL:
120 dB SPL at 3% THD.
Polarity:
Positive (inward) pressure on the
diaphragm produces positive voltage on pin 2
with respect to pin 3.
Operating voltage:
Phantom power, 12-48 volts DC
on pins 2 and 3 with respect to pin 1 of output
connector.
Current drain:
4 mA nominal.
Connector:
3-pin pro audio, XLR-M type.
Cable:
None supplied. Use two-conductor shielded
mic cable.
Materials:
High-impact molded plastic and steel
mesh mic grille, steel chassis.
300˚
270˚
240˚
330˚
0˚
30˚
FRONT
–0
–5
–10
–15
–20
REAR
1 kHz
200 Hz
5 kHz
60˚
90˚
120˚
lectern, install it on an open surface. Do not
install in a cavity or recessed area as the fre-
quency response and polar pattern will be
degraded.
Finish:
Satin black.
Net weight:
2.7 ounces (78 grams).
Dimensions:
See Fig. 4.
Fig. 3
210˚
180˚
150˚
Ceilings:
When mounting mics in the ceiling,
use as few mics as possible, and put them in
front of the people speaking
—not directly
overhead.
Note:
The system gain-before-feedback may
not be adequate in ceiling mount applications
because the mic is far from its user.
Optional accessories:
PH1A phantom power
supply (1 channel, battery or DC-adapter
powered). PH4A phantom power supply (4
channels, AC powered).
*1 pascal = 10 dynes/cm
2
= 10 microbars = 94 dB SPL.
30˚
0˚
Vertical-Plane Polar Response
60˚
90˚
120˚
1 kHz
200 Hz
5 kHz
FRONT
REAR
+
5
–0 –5 –10 –15 –
20
150˚
180˚
