Shure A27M User manual

Model A27M User Guide
©2004, Shure Incorporated
27B1424 (Rev. 3)
Printed in U.S.A.
STEREO MICROPHONE ADAPTER
The Shure model A27M is a stereo microphone adapter
designed to hold two microphones in selectable positions for
stereo broadcasting, recording or sound reinforcement. It
allows two microphones to share one stand without losing
independent positioning flexibility. The A27M permits coin-
cident or closely spaced mounting with a wide range of di-
rectional angles, and vertical microphone separations of 1
1/4 inches (31.8 mm), 2 5/8 inches (66.7 mm) or 4 inches
(102 mm).
The A27M consists of two vertically stacked sections that
rotate on their centers. Each contains a 5/8"-27 threaded
stud and locking ring to accept a variety of microphones.
The bottom section contains a 5/8"-27 adapter for mounting
on a microphone stand. A cable clamp for holding micro-
phone cables is included.
Installation
To install the A27M, follow these steps:
1. Determine the vertical separation between microphones
you desire. Minimum separation (coincident spacing) is
generally desirable, but it may be necessary to provide
greater spacing to accommodate the size or style of the
microphones. By repositioning the sections of the
A27M, the threaded studs may be 1 1/4 inches (31.8
mm), 2 5/8 inches (66.7 mm) or 4 inches (102 mm)
apart.
2. To reposition the sections, unscrew the knurled knob at
the top of the A27M and slide the two black sections off
the vertical rod. Reposition the sections with the studs
positioned for the vertical spacing desired. Replace the
knurled knob.
3. Attach the microphones or swivel adapters (such as the
Shure A57D or A57E) to the 5/8"-27 studs.
4. Attach the A27M to a microphone stand with a 5/8"-27
mounting thread.
5. Insert the microphones in the swivel adapters, loosen
the knurled knob on the top of the A27M, and position
the microphones for the desired response angles. The
top of the knurled knob contains reference marks every
45o; these may be used to position the microphones at
the desired angle (see Figure 1).
FIGURE 1
6. Tighten the knurled knob, attach the microphone cables,
and use the supplied cable clamp to fasten the micro-
phone cables to the A27M.
7. Raise the microphone stand to the desired height. Fig-
ure 2 shows a pair of Shure SM81 microphones
mounted in an “ORTF” configuration on the A27M.
FIGURE 2

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Stereo Recording Options
The A27M supports various popular pickup systems.
Those described below result in (1) improved imaging over
widely spaced microphones, and (2) superior depth repro-
duction over individually miked instruments. The spaced
microphone technique creates a stereo effect mainly be-
cause of differences in the arrival time of the sound at each
microphone. Coincident systems produce minimal arrival
time differences. The stereo effect they create is due to in-
terchannel amplitude differences. Closely spaced or
near-coincident placement lends both time and amplitude
differences to the stereo effect.
The table below describes five popular stereo pickup sys-
tems. It specifies microphone types, angles and spacing.
Those with coincident spacing have their diaphragms verti-
cally in line. Closely spaced microphones have their dia-
phragms separated by the specified distance. These and
other microphone systems are detailed in the book “Stereo
Microphone Techniques” by Bruce Bartlett (1991, Focal
Press. ISBN 0-240-80076-1) and in “Microphone Tech-
niques for Music Studio Recording” (AL1265) available from
Shure Incorporated.
Full Two Year Warranty
Shure warrants this product to be free in normal use of
any defects in workmanship and materials for two (2) years
from the date of purchase. If your Shure product fails within
this period, call 1-800-516-2525 in the United States for de-
tails on repair, replacement, or refund. In Europe, contact
Shure Incorporated Europe GMBH at [phone] or
[phone] (service hotline) or contact your autho-
rized Shure distributor. This warranty does not cover abuse
or misuse of the product, use contrary to Shure’s instruction,
ordinary wear and tear, an act of God or unauthorized repair.
Stereo Pickup systems Microphone Types Microphone Configurations
X-Y 2 Cardioid Axes of maximum response at
135o; spacing: coincident
ORTF (French
Broadcasting Corporation)
2 Cardioid Axes of maximum response at
110o; spacing: 17 cm. (7 in.)
NOS (Dutch Broadcasting
Foundation)
2 Cardioid Axes of maximum response at
90o;spacing: 30 cm. (12 in.)
Blumlein Pair or
stereosonic
2 Bidirectional Axes of maximum response at
90o; spacing: coincident
MS (Mid-Side) 1 Cardioid
1 Bidirectional
Cardioid and bidirectional
forward pointed;
spacing: coincident