Shure SM91A User Guide
The
meticulously optimized design of the SM91A in
cludes
a unique cartridge, developed at Shure. The re
is high sensitivity
sult
, exceptionally accurate sound re
production over the entire audio frequency range, and
freedom from of
f-axis coloration comparable to the fin
est unidirectional microphones.
The furnished ILP-1 preamplifier is a high-clipping
low-noise unit, phantom powered by 1
level
It
has selectable gain of 0 or +10 dB, and switchable low-
1 to 52
Vdc.
frequency response, flat or low cut (rolled off at 12 dB/
octave). The low cut is particularly useful to minimize
of ambient low-frequency noise from sources like
pickup
heating
or air-conditioner fans, for instance.
The SM91A consists of a small, rugged, surfacemounted microphone finished in professional durable
matte-black
enamel, a 7.6 m (25 ft) small diameter twoconductor shielded interconnecting cable with two
3-socket miniature Switchcraft connectors; and the
preamplifier
ILP-1
audio connector output.
sional
assembly with standard 3-pin profes
Features:
-
-
-
-
-
GENERAL
The
SM91A Microphone is
surface-mounted
applications. It is a professional-qual
designed specifically for
ity permanently-biased condenser microphone with a
half-cardioid
above
The SM91
pickup pattern (cardioid
the mounting surface.)
A t
ake
s a
dvantag
in the hemisphere
e of the w
ell-know
n p
rinciple that, at a barrier or boundary, sound pressure doubles
compared to its value if the boundary is removed. When
s
placed
ufficientl
y near the b
oundar
y s
urface
, a m
icrophone
has effectively 6 dB higher sensitivity and approximately 3
dB
g
reater rejectio
n o
f rando
m b
ackgroun
d n
oise.
Because of its half-cardioid polar pattern, the
SM91A surface-mounted microphone discriminates
against sounds originating from the rear, suiting the
SM91A
for conditions where an omnidirectional pattern
makes other surface-mounted microphones impractical.
The intrinsic unidirectionality of the SM91A can be
a
great benefit when it is desirable to isolate a particular
vocalist, instrument, or group from the rest of an ensemble being recorded. Because of a cardioid pickup
pattern, no physically isolating barriers are required,
and
directionality is maintained to low frequencies.
The SM91A can be used for individual instrument
pickup,
e.g., mounted inside the lid of a grand piano or
on the floor next to a bass drum. Experimental placement
and critical listening will help to determine the best
location
for any particular purpose or ef
fect desired.
• Wide flat frequency response for faithful sound reproduction
•
High sensitivity
across the audio spectrum
, low self-noise
-
• V
ery low distortion and high output clipping level
• Half-cardioid polar pattern minimizes pickup from
rear of microphone, permits aiming microphone,
toward performers and away from audience, or
e.g.,
toward
singers and away from instruments
•
Low susceptibility to RFI,
electrostatic and electro
magnetic hum
• Extremely
and
• Switch-selectable
off
permits tailoring response to suit conditions
•
Switch selectable preamp gain of 0 or +10 dB
• Accepts phanto
of
wide v
• Standard
preamp
rugged construction of both microphone
preamplifier for outstanding reliability
12 dB/octave low-frequency
m p
owe
r o
f 11 t
o 5
2 Vdc, p
ariet
y o
f a
mplifier
s o
r phanto
m s
3-pin male XLR-type output connector on
can
be directly connected to any 3-pin fe
male XLR-type phantom-powered input
• Low profile and matte black finish for unobtrusive
appearance on-camera or onstage; on floor,
ceiling, wall, or lectern
• Usable over very wide range of temperature and hu midity
ermit
upplies
table,
cut
s u
-
-
se
-
Copyright 1993, Shure Brothers Inc.
27A2669(MC)
Printed in U.S.A.
SPECIFICATIONS
Type
d c
Cardioi
ondenser (electre
t b
ias) for surfac
e m
ounting
Frequency Response
20 to 20,000 Hz (see Figure 1)
TYPICAL FREQUENCY RESPONSE
(measured at 30o incidence to infinite surface)
FIGURE 1
Polar Pattern
Half-cardioid
(cardioid in
hemisphere above mounting
surface), uniform with frequency, symmetrical about
axis (see Figure 2)
TYPICAL POLAR P
ATTERN
FIGURE 2
Output Impedance
Rated at 150
Recommended minimum load impedance: 800
(May
be used with loads as low as 150 Ω with reduced
clipping
Output
at
Level
30o incidence to flat surface)
Open Circuit V
0
dB = 1 V
Ω (90 Ω
actual)
level)
(at 1,000 Hz, measured
oltage
.
. . . . . . . .
/µbar
Ω
with sound source
–71.5 dB (0.27 mV)
Preamplifier Output Clipping Level (at 1,000 Hz, less
than
0.1% THD)
GAIN
800 Ω load
150 Ω load
.
. . . . . . . . . . . . . .
.
. . . . . . . . . . . .
–13.0 dBV –21.0 dBV
0
0 dBV
(1.0
V)
+10
–7.0 dBV
(0.45 V)
.
(0.22 V) (0.09 V)
Maximum SPL
(at 1,000 Hz, less than 1% THD)
800 Ω load
ILP-1 gain set at 0 dB
ILP-1
gain set at +10 dB
150 Ω
load
ILP-1 gain set at 0 dB
ILP-1
gain set at +10 dB
Electromagnetic
Hum Pickup
.
. . . . . . . . . . . . .
.
. . . . . . . . . .
.
. . . . . . . . . . . . .
.
. . . . . . . . . .
(maximum)
–0.5 dB equivalent SPL in 1 mOe field (60 Hz)
Preamplifier Controls
Selectable Low-Frequency Response: Flat/Low Cut
(12
dB/octave rollof
f below 80 Hz)
Selectable Gain: 0/+10 dB
Output Noise
25.5 dB SPL, A-weighted
32 dB SPL, C-weighted
28.5 dB SPL per DIN 45 405
Signal-to-Noise Ratio
68.5 dB re 94 dB SPL
Dynamic Range
121 dB (800 Ω load, gain set at 0 dB)
Phasing
Positive pressur
age
o
n pin 2 r
e on d
elativ
iaphrag
e t
o pin 3 o
m p
f p
roduce
ream
p o
s p
ositive volt-
utpu
t c
Power
to 52 Vdc phantom (simplex) voltage
11
(operational
down to 9 Vdc with reduced clipping level); current
drain
2.2 mA at 52 Vdc, 1.8 mA at 1
1 Vdc
Case
Microphone: Matte black enamel die-cast base and
perforated steel grille with replaceable or cleanable
fine
mesh screen and foam pad wind/dirt barrier
Preamplifier: Matte black enamel finished steel
Cable
7.6
m (25
ft) two-conductor shielded, small diameter
with Switchcraft Tini (Q.G.) 3-pin (female) connector
on
each end
Environmental Conditions
Operating Temperature: –18 to 57o C (0 to 135o F)
Storage T
emperature: –29 to 74o C (–20 to 168o F)
Relative Humidity: 0 to 95%
Dimensions
See Figure 3
OVERALL DIMENSIONS
FIGURE 3
146.5 dB
136.5 dB
129.5 dB
1
18.5 dB
onnector
,
2.
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