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 coincident or closely spaced mounting with a wide range of directional 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 microphone cables is included.
To install the A27M, follow these steps:
The A27M supports various popular pickup systems. Those described below result in (1) improved imaging over widely spaced microphones, and (2) superior depth reproduction over individually miked instruments. The spaced microphone technique creates a stereo effect mainly because 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.
|Stereo Pickup Systems||Microphone Types||Microphone Configurations|
|X-Y||2 Cardioid||Axes of maximum response at 135°; spacing: coincident|
|ORTF (French Broadcasting Corporation)||2 Cardioid||Axes of maximum response at 110°; spacing: 17 cm. (7 in.)|
|NOS (Dutch Broadcasting Foundation)||2 Cardioid||Axes of maximum response at 90°; spacing: 30 cm. (12 in.)|
|Blumlein Pair or stereosonic||2 Bidirectional||Axes of maximum response at 90°; spacing: coincident|
|MS (Mid-Side)||1 Cardioid
|Cardioid and bidirectional forward pointed; spacing: coincident|
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 details on repair, replacement, or refund. In Europe, contact Shure Incorporated Europe GMBH at +49 (7262) 924911 4 or +49 (7262) 924-90 (service hotline) or contact your authorized 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.