Description
Earthworks M30BX is an omnidirectional
(pressure) microphone designed and calibrated
for measurement purposes. It is a prepolarized
condenser microphone directly coupled to a
wideband, low output impedance preampli-
fi er. The M30BX requires a single type P28L
(Lithium) or 4LR44 or equivalent 6V battery
as a power source. It features a linear free-fi eld
frequency response from 9Hz to 30kHz (please
see the enclosed individual calibration chart),
very low handling noise, uniform polar pattern,
and has 6dB of extra gain available. Its unique
circuitry excludes the transconductance of the
input FET from the overall gain structure. This
means the sensitivity remains very stable when
the microphone is subjected to variations in
ambient temperature. The M30BX meets or
exceeds ANSI Type 1 requirements.
Each microphone is delivered with its own
calibration chart providing its individually mea-
sured open-circuit sensitivity for both gain posi-
tions, and the frequency response curve. A com-
puter fi le containing the frequency response
data for importing directly into measurement
software is available from Earthworks, Inc. upon
request at an extra cost. A mounting clip, a cali-
brator adapter, an XLR to RCA adapter, and a
battery are included with the microphone.
Applications
Earthworks M30BX is ideally suited for on-
location acoustical measurements including
loudspeaker design and quality control, sound
system setup and troubleshooting, room acous-
tics, or any application where an accurate free-
fi eld measurement microphone is required and
portability is important or a power source is not
readily available. Many test systems manufactur-
ers, such as DRA Labs (MLSSA™), Smaart™
and DEQX™, are recommending M30BX
microphones. The wide linear minimum-phase
response and fast well-damped impulse response
(Fig. 2) make M30BX an excellent microphone
for loudspeaker design, especially for time do-
main measurements.
The M30BX is simple to operate. Make sure
the battery (included) is properly installed in
the microphone. To open the battery compart-
ment hold the microphone by the upper body
and unscrew the lower, larger part of the micro-
phone (this cover is not removable). The battery
is only switched on when an XLR connector
is plugged into the microphone. The M30BX
will not operate from phantom power.
The M30BX will drive either balanced or
unbalanced inputs. An XLR to RCA adapter is
enclosed for driving unbalanced inputs of sound
cards directly. Please note that the best S/N ratio
is achieved using a balanced interface.
Inside the battery compartment there is a gain
switch. At the “0dB” setting the M30BX has nor-
mal condenser sensitivity. At the “6dB” setting the
extra dB of gain is applied, eliminating a need for
an external preamplifi er for most applications.
For optimum results we recommend point-
ing the M30BX toward the sound source.
Calibration
The microphone is calibrated at the factory at
1 kHz (therefore independent of any frequency
weighting). The sensitivity in mV/Pa is provided
on the calibration chart for both gain positions.
Make sure to use the actual data rather than re-
lying upon the nominal 14dB gain fi gure. If on-
site calibration is required, use the enclosed one
half inch standard calibration adapter.
Specifi cations
Frequency response: 9Hz to 30kHz +1/-3dB
Polar Pattern: Omnidirectional
Sensitivity: 30mV/Pa (Typical)
with 6dB Gain 60mV/Pa (Typical)
Power Requirements: 6V Battery Type P28
(2CR-1/N, 4LR44 or eq.)
Peak Acoustic Input: 130dB SPL
with 14dB Gain 124dB SPL
Output:
XLR (Fig. 1)
Minimum Load: 600
Ω
btw. pins 2 & 3
Noise:
22dB, A equivalent
Dimensions L x D: 220 x 23 mm
(8.65 x .910 in.)
Weight:
180g (.4lb)
Compliant
Specifi cations are subject to change without notice.
Fig 1. XLR Output Connector Assignment of M30BX
Fig 2. Impulse Response (Typical) of M30BX
Fig 3. Polar Response (Typical) of M30BX, 1dB/div.
