Architects and Engineers Specifications
The microphone shall be a fixed-charge
condenser with a cardioid polar pattern and a
frequency response of 40 Hz to 20,000 Hz. It
shall operate from an external 9V to 52V DC
phantom power source or, alternatively, from
a 1.5V AA / UM3 battery. Nominal open-
circuit output voltage shall be 6.3 mV (phan-
tom) or 5.6 mV (battery) at 1 kHz, 1 Pascal.
Output with the included power module shall
be low impedance balanced (200 ohms-phan-
tom, 270 ohms-battery).
The microphone shall have a permanently-
attached 6' (1.8 m) miniature cable between
the microphone and power module. The
power module shall house the battery and
contain an off/on/low-roll-off switch. The
power module shall terminate in a 3-pin
XLRM-type connector.
The microphone shall be mountable in an
included instrument adapter or clothing clip.
The microphone shall be 0.98" (25.0 mm)
long with a diameter of 0.39" (10.0 mm). The
microphone weight shall be 0.1 oz (2.8
grams). Finish shall be low-reflectance black.
The Audio-Technica AT831b is specified.
Description
The AT831b is a miniature condenser
microphone with a cardioid polar pattern. It
has been designed for hands-free
applications in sound reinforcement systems,
and for use by professional musicians,
especially for pickup of acoustic guitar. The
AT831b provides improved gain before
feedback that normally cannot be achieved
with miniature omnidirectional microphones.
Close-up voice and instrument pickup are
crisp and clean, yet full sounding, while
suppression of background noise is
significantly improved over that of stand-
mounted full-size cardioid microphones.
Audio -Technica design engineers have
utilized the newest low-mass technology in
the quest for superior performance. The
permanent charge is now on the fixed back
plate, rather than the moving element. With
A-T fixed charge “back plate“ construction, a
gold-vaporized diaphragm just 2 microns
thick (about 0.000079") can be used. This
reduces moving mass, thus improving
frequency response and transient response
while reducing distortion.
The AT831b can be powered from an external
9V to 52V DC phantom supply or from
an AA/UM3 1.5V battery (supplied). Current
demands are so low that an alkaline
battery will provide about 1200 hours of
continuous use.
The microphone element is enclosed in a
rugged housing with low-reflectance finish.
Internal construction is designed to minimize
handling and clothing noise. A 6' (1.8 m)
cable is provided between the microphone
and power module. A built-in 3-position
switch on the power module allows selection
of off, on/flat response, or on/low-roll-off. An
AT8417 clothing clip and AT8444
guitar adapter are provided, as well as an
accessory AT8116 windscreen. The
microphone is well protected by a specially-
designed carrying case.
Operation and Maintenance
To install the battery, remove the cap from
the top of the power module. Insert the
battery, being certain to observe battery
polarity as marked (+ end toward the cap
release button). For longest battery life, the
switch should remain off except when the
microphone is in use. While standard carbon-
zinc AA batteries will operate the microphone
satisfactorily, alkaline or mercury cells are
preferred for longer service life. Only
“leakproof” batteries should be used. The
battery does not have to be in place to use in
phantom power mode. Phantom power
requires 9V to 52V DC.
The microphone may be worn on the person
or attached to a musical instrument. If used
with an instrument, it may be attached by
means of the clothing clip or the special
instrument adapter provided. The power
module may be worn on the belt, utilizing the
belt clip, or located in any convenient place.
An open-pore foam windscreen simply slips
over the head of the microphone, effectively
reducing wind noise or “popping” when
used extra close.
Output is low impedance balanced. The
XLRM-type output connector mates with
XLRF-type cable connectors. The balanced
signal appears across Pins 2 and 3, while the
ground (shield) connection is Pin 1. Output is
phased so that positive acoustic pressure
produces positive voltage at Pin 2 in accor-
dance with industry convention.
While a modern condenser microphone is not
unduly sensitive to the environment, temper-
ature extremes can be harmful. Exposure to
high temperatures can result in gradual and
permanent reduction of the output level.
Avoid leaving the microphone in the open sun
or in areas where temperatures exceed 110° F
(43° C) for long periods of time. Extremely
high humidity should also be avoided.
AT831b
MINIATURE
CARDIOID
CONDENSER
MICROPHONE
Frequency Response
Roll-off
LEGEND
12" or more on axis
10 dB
10k
20k
Response in dB
2k
500
1k
Frequency in Hertz
100
200
50
5k
