Shure SM91A User Manual

GENERAL
The SM91A Microphone is designed specifically for
surface-mounted applications. It is a professional-qual-
ity permanently-biased condenser microphone with a
half-cardioid pickup pattern (cardioid in the hemisphere
above the mounting surface.)
The SM91A takes advantage of the well-known princi-
ple that, at a barrier or boundary, sound pressure doubles
compared to its value if the boundary is removed. When
placed sufficiently near the boundary surface, a microphone
has effectively 6 dB higher sensitivity and approximately 3
dB greater rejection of random background noise.
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 impracti-
cal. 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 en-
semble 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 place-
ment and critical listening will help to determine the best
location for any particular purpose or effect desired.
Copyright 1993, Shure Brothers Inc.
27A2669(MC)
The meticulously optimized design of the SM91A in-
cludes a unique cartridge, developed at Shure. The re-
sult is high sensitivity, exceptionally accurate sound re-
production over the entire audio frequency range, and
freedom from off-axis coloration comparable to the fin-
est unidirectional microphones.
The furnished ILP-1 preamplifier is a high-clipping
level low-noise unit, phantom powered by 11 to 52 Vdc.
It has selectable gain of 0 or +10 dB, and switchable low-
frequency response, flat or low cut (rolled off at 12 dB/
octave). The low cut is particularly useful to minimize
pickup of ambient low-frequency noise from sources like
heating or air-conditioner fans, for instance.
The SM91A consists of a small, rugged, surface-
mounted microphone finished in professional durable
matte-black enamel, a 7.6 m (25 ft) small diameter two-
conductor shielded interconnecting cable with two
3-socket miniature Switchcraft connectors; and the
ILP-1 preamplifier assembly with standard 3-pin profes-
sional audio connector output.
Features:
Wide flat frequency response for faithful sound re-
production across the audio spectrum
High sensitivity, low self-noise
Very low distortion and high output clipping level
Half-cardioid polar pattern minimizes pickup from
rear of microphone, permits aiming microphone,
e.g., toward performers and away from audience, or
toward singers and away from instruments
Low susceptibility to RFI, electrostatic and electro-
magnetic hum
Extremely rugged construction of both microphone
and preamplifier for outstanding reliability
Switch-selectable 12 dB/octave low-frequency cut-
off permits tailoring response to suit conditions
Switch selectable preamp gain of 0 or +10 dB
Accepts phantom power of 11 to 52 Vdc, permits use
of wide variety of amplifiers or phantom supplies
Standard 3-pin male XLR-type output connector on
preamp 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, table,
ceiling, wall, or lectern
Usable over very wide range of temperature and hu-
midity
Printed in U.S.A.