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Maximum SPL (at 1,000 Hz)
800 Ω load
. . . . . . . . . . . . . . . . .
150 Ω load
. . . . . . . . . . . . . . . . .
Hum Pickup
–3 dB equivalent SPL in a 1 mOe field (60 Hz)
Self-Noise (equivalent sound pressure levels; measured
with true rms voltmeter)
16 dB typical, A-weighted
19 dB typical, weighted per DIN 45 405
Signal-to-Noise Ratio
78 dB (IEC 651)* at 94 dB SPL
*S/N ratio is difference between microphone output at 94 dB SPL
and microphone self-noise A-weighted.
Overvoltage and Reverse Polarity Protection
Max. external voltage applied to pins 2 and 3 with
respect to pin 1
. . . . . . . . . . . . . . . . . . . . . .
Reverse polarity protection
Polarity
Positive pressure on diaphragm produces positive volt-
age on pin 2 relative to pin 3
Cartridge Capacitance
54 pF
Low Frequency Response Switch Positions
Flat; –6 dB/octave below 100 Hz; –18 dB/octave below
80 Hz
Attenuator Switch Positions (Lockable)
0 or –10 dB
Power
Supply Voltage
. .
11 to 52 Vdc, positive, pins 2 and 3
Current Drain
. . . . . . . . . . . . . . . . . . . . . . . .
Environmental Conditions
Temperature:
Storage
. . . . . . . . . . . . . . . . . . . . . . . .
Operating
. . . . . . . . . . . . . . . . . . . . . .
Humidity:
Storage
. . . . . . . . .
temperature (72_to 80_ F, 22_ to 27_ C)
Case
Steel construction with vinyl metallic paint finish and
stainless steel screens
23.5 mm
136 dB (attenuator at 0)
146 dB (attenuator at –10)
128 dB (attenuator at 0)
138 dB (attenuator at –10)
+ 52 Vdc
. . . . . . . . . . . .
200 mA max.
(diode-clamped)
1.2 mA max.
– 29_ to 74_ C
(–20_ to 165_ F)
– 6.7_ to 49_ C
(20_ to 120_ F)
0–95% relative humidity at room
OVERALL DIMENSIONS
Dimensions
See Figure 3
Weight
Net
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Packaged
. . . . . . . . . . . . . . . . . .
Certification
Eligible to bear CE marking. Conforms to European
EMC Directive 89/336/EEC. Meets applicable tests and
performance criteria in European EMC Standard EN
55103 (1996) parts 1 and 2 for residential (E1) and light
industrial (E2) environments.
OPERATION
Power
The SM81 requires phantom power. This may be supplied
to the microphone by a mixer, preamplifier or console with built-
in phantom power or from an external power supply (such as
the Shure model PS1A). Phantom power sources providing be-
tween 11 and 52 Vdc are suitable.
Use only high-quality cables because intermittent shorts
between broken shield wires and balanced conductors will
cause extremely large noise transients in the system. Avoid
ground loops due to grounded connector shells or the micro-
phone case touching other grounded metal objects. Follow
generally accepted audio grounding practices.
Impedance
A minimum load impedance of 800 Ω or greater should be
used for maximum signal handling and minimum distortion. The
load may be as low as 150 Ω, but a reduction in output clipping
level will result. It should be noted that the power supply itself
may add loading (3300 Ω in the Shure PS1A power supply) to
the microphones.
PS1A Power Supply
When using the Shure PS1A to phantom power the SM81,
connect the microphone cable to the SM81 and to the MICRO-
PHONE connector of the power supply. The power supply uses
the balanced audio cable pair to carry the supply current to the
microphone and the cable shield as a ground return.
Connect the OUTPUT connector of the power supply to a
low-impedance microphone input of a mixer, audio console or
tape recorder. A second SM81 may be connected to the re-
maining power supply channel in a similar manner.
212 mm
FIGURE 3
2
230 grams (8 oz)
740 grams (1 lb 10 oz)
20.1 mm
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