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Shure SM81 User Manual

Page 2

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Maximum SPL (at 1,000 Hz)

800 Ω load: . . . . . . . . . . . . . . . . . . . . . 136 dB (attenuator at 0)

146 dB (attenuator at -10)

150 Ω load: . . . . . . . . . . . . . . . . . . . . . 128 dB (attenuator at 0)

138 dB (attenuator at -10)

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: . . . . . . . . . . . . . . . . . . . . . . . . . +52 Vdc

Reverse polarity protection: . . . . . . . . . . . . . . . . 200 mA max.

(diode-clamped)

Polarity

Positive pressure on diaphragm produces positive voltage 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: . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 mA max.

Environmental Conditions

Temperature

Storage: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –29° to 74° C

(–20° to 165° F)

Operating:. . . . . . . . . . . . . . . . . . . . . . . . . . . . –6.7° to 49° C

(20° to 120° F)

Humidity

Storage: . . . . . . . . . . . . . . 0–95% relative humidity at room

temperature (72° to 80° F, 22° to 27° C)

Case

Steel construction with vinyl metallic paint finish and stainless

steel screens

Dimensions

See Figure 3

Weight

Net: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 grams (8 oz)

Packaged: . . . . . . . . . . . . . . . . . . . . . . . 740 grams (1 lb 10 oz)

Certification

Eligible to bear CE marking. Conforms to European EMC Direc-

tive 89/336/EEC. Meets applicable tests and performance cri-

teria 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 phan-
tom power or from an external power supply (such as the Shure
model PS1A). Phantom power sources providing between 11 and
52 Vdc are suitable.

Use only high-quality cables because intermittent shorts be-

tween broken shield wires and balanced conductors will cause ex-
tremely large noise transients in the system. Avoid ground loops
due to grounded connector shells or the microphone 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 load-
ing (3300 Ω in the Shure PS1A power supply) to the microphones.

PS1A Power Supply

When using the Shure PS1A to phantom power the SM81, con-

nect the microphone cable to the SM81 and to the MICROPHONE
connector of the power supply. The power supply uses the bal-
anced audio cable pair to carry the supply current to the micro-
phone 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 remaining pow-
er supply channel in a similar manner.

OVERALL DIMENSIONS

FIGURE 3

212 mm

20 mm

23.5 mm