Description
The AT871R is a wide-range condenser micro-
phone with a hemi-cardioid (half-space cardioid)
polar pattern. It is useful in surface-mounted
applications such as high-quality sound rein-
forcement, professional recording, television,
and other demanding sound pickup applications.
Supplied as a cardioid, the AT871R easily
accepts interchangeable elements to permit
selection of angle of acceptance from 100° to
360°. The following optional elements are
available from an authorized Audio-Technica
dealer or the A-T service department:
AT853H-ELE hypercardioid, AT853O-ELE
omnidirectional, AT853SC-ELE subcardioid.
Positioning a properly designed miniature
cardioid microphone centrally on a large, flat,
unobstructed surface yields several distinct
advantages. Directionality is increased by 3 dB,
promoting enhanced gain before feedback
and further suppression of ambient noise.
Sensitivity is increased for improved signal to
noise ratio. Phase distortion due to reflected
sound energy from the boundary itself is
eliminated.
The AT871R is powered from an external 9V
to 52V DC phantom power supply. A 25' (7.6 m)
cable is provided with TA3F and XLRM-type
connectors for use between the microphone
and electronics input.
The microphone element is enclosed in a
rugged die-cast case and protected by two
layers of perforated steel. The combination of
heavy die-cast case and rubber non-slip bottom
pad minimizes mechanical coupling of surface
vibrations to the microphone. The low-profile
housing has a low-reflectance black finish.
The microphone is also available in white as
the AT871RW, with a white-finished micro-
phone housing and cable.
Installation and Operation
The symmetry and area of the mounting surface
directly affect the sensitivity of the boundary
microphone at low frequencies. Ideally, the
mounting surface should be circular; however,
square or rectangular surfaces are most often
used. If the mounting surface is rectangular,
the smaller dimension tends to determine
the low-frequency cutoff. The microphone
should be centered on the surface and
positioned with the front of the microphone
facing the sound source along the longer
dimension of the mounting surface. The
sound source should not be below, or higher
than 60° above, the plane of the mounting
surface.
pressure produces positive voltage at Pin 2 in
accordance with industry convention.
While a modern condenser microphone is
not unduly sensitive to the environment,
temperature 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.
Architects and Engineers Specifications
The microphone shall be a fixed-charge con-
denser with a hemi-cardioid polar pattern
designed for use in surface-mount boundary
applications. The frequency response shall be
30 Hz to 20,000 Hz. The microphone shall
operate from an external 9V to 52V DC
phantom power source. Nominal open-circuit
output voltage shall be 22.4 mV at 1 kHz, 1
Pascal. Output shall be low impedance bal-
anced (200 ohms).
A 25' (7.6 m) cable with TA3F to XLRM-type
connectors shall be supplied for connection
between the microphone and electronics
input. The microphone shall have a maximum
width of 4.72" (120.0 mm) and a maximum
length of 5.71" (145.0 mm). Weight shall be
14.6 oz (415 grams). The microphone shall be
housed in a die-cast case with a two-layer
perforated steel grille. Finish shall be low-
reflectance black [white].
The Audio -Technica AT871R [AT871RW] is
specified.
Output is low impedance balanced. The bal-
anced signal appears across Pins 2 and 3
while the ground (shield) connection is Pin 1.
Output is phased so that positive acoustic
AT871R
AT871RW
UNIDIRECTIONAL
CONDENSER
BOUNDARY
MICROPHONES
Frequency Response
12" or more on axis (flat)
LEGEND
Frequency in Hertz
Response in dB
10 dB
20k
10k
5k
2k
1k
500
200
100
50
