Shure Model A27M Stereo Microphone Adapter User Guide
Brand: Shure
Product Overview
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.
Installation
- 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.
- 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.
- Attach the microphones or swivel adapters (such as the Shure A57D or A57E) to the 5/8"-27 studs.
- Attach the A27M to a microphone stand with a 5/8"-27 mounting thread.
- 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 45°; these may be used to position the microphones at the desired angle (see Figure 1).
- Tighten the knurled knob, attach the microphone cables, and use the supplied cable clamp to fasten the microphone cables to the A27M.
- Raise the microphone stand to the desired height. Figure 2 shows a pair of Shure SM81 microphones mounted in an “ORTF” configuration on the A27M.
Figure 1 Description: Illustrates the adjustment of microphone angles. It shows one microphone positioned at 0 degrees (parallel) and another at 45 degrees from parallel, indicating the range of motion controlled by the knurled knob.
Figure 2 Description: Shows a pair of Shure SM81 microphones mounted on the A27M in an "ORTF" configuration, demonstrating a common stereo recording setup.
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 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 interchannel 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 systems. It specifies microphone types, angles and spacing. Those with coincident spacing have their diaphragms vertically in line. Closely spaced microphones have their diaphragms 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 Techniques 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, 1 Bidirectional | Cardioid and bidirectional forward pointed; spacing: coincident |
Guarantee
This Shure product is guaranteed in normal use to be free from mechanical defects for a period of one year from date of purchase. Please retain proof of purchase date. This guarantee includes all parts and labor. This guarantee is in lieu of any and all other guarantees or warranties, express or implied, and there shall be no recovery for any consequential or incidental damages.
Shipping Instructions
Carefully repack the unit, have it insured, and return it prepaid to: Shure Incorporated. Attention: Service Department, 222 Hartrey Avenue, Evanston, Illinois 60202-3696. Outside the United States, return the unit to your dealer or Authorized Shure Service Center for repair. The unit will be returned to you prepaid.
