Shure SM81 User Manual

MODEL SM81

UNIDIRECTIONAL CONDENSER MICROPHONE

The Shure Model SM81 is a high-quality, unidirectional
condenser
fessional applications in studio recording, broadcasting, and
sound
quiring
tortion characteristics, very low RF susceptibility, and reliable
operation over a wide range of temperature and humidity
extremes.
a stainless steel screen, and finished in durable vinyl paint.

uator lock, windscreen, and carrying/storage case. It is sup­plied
pop-filter
A81WS), a compact, lightweight microphone stand (Model
S15)
crophone
power supply (Model PS1A). An alternative omnidirectional
cartridge (Model R104A) is also available.

microphone designed for the

reinforcement. It is especially suitable

extremely wide frequency

The case is constructed

The microphone is furnished with a swivel adapter, atten-

without cable. A

grille (Model A81G), a heavy-duty windscreen (Model

capable of extension to 4.3 m (14 ft), a versatile stereo mi

adapter (Model A27M), and a dual-channel phantom

vailable accessories are a highly ef

most demanding pro

for applications re

response, low noise and dis

of steel for ruggedness, with

ficient

Model SM81 Features:

•

Wide-range, frequency response for exceptionally accu-

rate recording and sound reinforcement applications

•

Low noise and high output clipping level characteristics

•

Low distortion characteristics over the entire audio spec-

trum for a wide range of load impedances

•

Cardioid polar pattern, uniform with frequency and sym-

metrical about axis, to provide maximum rejection and

minimum coloration of off-axis sounds

•

Very low RF susceptibility

•

Selectable

rolloff

•

10 dB attenuator accessible without disassembly; lockable

in either position

•

Wide-range phantom powering includes DIN 45 596 volt-

ages of 12 and 48 Vdc

•

Rugged construction for outstanding reliability

•

Field-usable

conditions

low-frequency response: flat, 6 or 18

over wide range of temperature and

dB/octave

humidity

Shure

Brothers Incorporated

222 Hartrey A

venue

Evanston IL 60202-3696 U.S.A.

Model SM81 User Guide

SPECIFICATIONS

Type

Cardioid

Frequency Response

20 to 20,000 Hz (see Figure 1)

-

-

-

Polar Pattern

cy, symmetrical about axis (see Figure 2)

-

Output Impedance

Output

Open Circuit Voltage –65 dB (0.56 mV).

Equivalent Power Level –40.5 dB.

Clipping

800 Ω Load –4 dBV (0.63 V).
150 Ω

TYPICAL FREQUENCY RESPONSE

FIGURE 1

Cardioid

(unidirectional) response—uniform with frequen

TYPICAL

POLAR P

FIGURE 2

Rated at 150 ohms (85 Ω actual)
Recommended minimum load impedance: 800 Ω (May
be used with loads as low as 150 Ω with reduced clip­ping level)

Level (at 1,000 Hz)

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .

Level (at 1,000 Hz)

. . . . . . . . . . . . . . . . . . . . . . . . .

Load

–15 dBV (0.18 V).

. . .

. . . . . . . . . . . . . . . . . . . .

-

ATTERNS

(0 dB = 1 volt per µbar)

(0 dB = 1 milliwatt per 10 µbars)



1996, Shure Brothers Inc.

27A2916

(P

A)

Printed in U.S.A.

T

otal Harmonic Distortion

Less than 0.5% (131 dB SPL at 250 Hz into 800 Ω

Maximum

SPL (at 1,000 Hz)

136 dB (attenuator at 0); 146 dB (attenuator at 10)
with 800 Ω

load
128 dB (attenuator at 0); 138 dB (attenuator at 10)
with 150 Ω

Hum

Pickup

load

–3 dB equivalent SPL in a 1 moe field (60 Hz)

Output

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

Overvoltage

Max. External V
to Pins 2 and 3 with Respect to Pin 1 + 52 Vdc.

and Reverse Polarity Protection

oltage Applied

. . . . . . .

Reverse Polarity
Protection 200 mA max. (diode-clamped).

. . . . . . . . . . . . .

Phasing

Positive pressure on diaphragm produces positive voltage

on pin 2 relative to pin 3

Cartridge

Capacitance

54 pF

LP

Response Switch

Flat,

–6 dB/octave below 100 Hz, –18 dB/octave below 80

Hz

Attenuator

Switch

0 or 10 dB (120 pF)

Power

Supply V
Current Drain 1.0 mA to 1.2 mA.

oltage

. . . . . .

11 to 52 Vdc, positive pins 2 and 3.

. . . . . . . . . . . . . . . . . . . . . .

Environmental Conditions

Relative Humidity 0–50%

. . . . . . . . . . . . . . .

– 29

 to 74 C.

(–20 to 165 F)

Relative Humidity 0–95%

. . . . . . . . . . . . . .

– 29

 to 57 C.

(–20 to 135 F)

Connector

Professional 3-pin audio**

Case

Steel

construction with metallic vinyl paint finish and stain

less steel screen

Dimensions

See Figure 3

load)

Weight

Net 230 grams (8 oz).

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Packaged 1.2 kg (2 lb 10 oz).

*S/N

ratio is dif

phone
**Designed

equivalent

. . . . . . . . . . . . . . . . . . . . . . . . .

ference between microphone

self-noise A-weighted.

to mate with Cannon XL series,

connectors.

output at 94 dB SPL and micro

Switchcraft A3 (Q.G.) series or

Certification

Conforms

marking;

to European Union directives, eligible to bear

meets European Union EMC Immunity Requirements
(EN 50 082–1, 1992); RF radiated (IEC 801–3); ESD (IEC
801–2); EFT (IEC 801–4).

OPERATION

The SM81 is designed for phantom powering by Shure

Model

PS1A Power Supply

er supply providing 12 to 48 Vdc phantom voltage.

Use only high-quality cables, as intermittent shorts be-

tween

broken shield wires and balanced
extremely 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.

Paralleling or “Y-ing” the SM81 with another microphone
(two microphones on the same input) is not recommended;
separate inputs are preferable. However, paralleling two
SM81’s may be accomplished with either a reduction in maxi­mum

SPL and output level, or a reduction only in
the microphones are electrically isolated. With the micro­phones
the

paralleled either before or

maximum SPL is reduced by approximately 10
output level by 6 dB. The reduction in maximum SPL can be
avoided by using either two Shure A15AS Attenuators and a
Switchcraft 391Q43 Y-Adapter to isolate the microphones, or
an

isolation network as shown in Figure 4. The network
each microphone output level by 8 dB, while the A15AS re­duces

the output level by 5 dB plus the attenuator’s 15, 20, or 25
dB (switch-selectable). The network or attenuators can be in­serted between the power supply outputs and mixer input, or
between two microphones and a single power supply input.
Note

that a PS1A Power Supply can power two SM81’

input;

other power supplies should be checked to see if they can

supply

a minimum of 10 Vdc at each microphone when both mi

crophones are connected.

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
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.

, or by virtually any microphone pow

conductors will cause

after a PS1A Power Supply

-

CE

-

output level if

,

dB and the

reduces

s on each

-

clipping

OVERALL DIMENSIONS

FIGURE 3

2