The SM91 Microphone is designed specifically for surface-mounted applications. It is a professionalquality permanently-biased condenser microphone with a half-cardioid directional pattern (cardioid in the hemisphere above the mounting surface.)
The SM91 takes advantage of the well-known principle 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 SM91 surface-mounted microphone discriminates against sounds originating from the rear, suiting the SM91 for conditions where an omnidirectional pattern makes other surface-mounted microphones impractical. The intrinsic unidirectionality of the SM91 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 SM91 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 demonstrate the best location for any particular purpose or effect desired.
The meticulously optimized design of the SM91 includes a totally new cartridge, developed at Shure. The result is high output, notably accurate sound reproduction over the entire audio frequency range, and off-axis performance comparable to the finest unidirectional microphones. The supplied low-distortion, highCopyright 1988, Shure Brothers Inc 27A2161 (HD) clipping-level preamplifier provides switch-selectable Flat or Low-Cut response for further assistance in obtaining the best possible microphone signal even under difficult conditions.
The SM91 is powered either by two readily available 9-volt alkaline batteries (300 hours continuous battery life) or by an 11-to-52 Vdc simplex (phantom) supply from broadcast, sound-reinforcement, or recording equipment. The system is designed so that the battery supply will automatically switch in should the simplex power fail.
The SM91 consists of a small, rugged, surfacemounted microphone finished in professional durable matte-black enamel; a 7.6m (25 ft) small diameter twoconductor shielded interconnecting cable with two 3-socket miniature Switchcraft connectors; and a sturdy preamplifier assembly with battery compartment, battery On/Off switch, green LED battery-condition indicator, low-frequency Flat/Lo Cut switch, and standard 3-pin professional audio connector output.
- Wide flat frequency response for accurate sound reproduction across the audio spectrum
- Switch-selectable 12 dB/octave low-frequency cutoff permits tailoring response to suit conditions
- 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
- High sensitivity and high signal-to-noise-ratio
- Very low distortion and high output clipping level
- Battery or simplex powering: uses standard 9-volt alkaline batteries; accepts wide range of simplex voltages - 11 to 52 Vdc
- Low susceptibility to RFI, electrostatic and electromagnetic hum
- Extremely rugged construction of both microphone and preamplifier for outstanding reliability
- 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 humidity
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