Shure SM91

Type: Cardioid condenser (electret bias) for surface mounting
Frequency Response: 20 to 20,000 Hz at 30° incidence to infinite surface
Polar Pattern: Half-cardioid (cardioid in hemisphere above mounting surface), uniform with frequency, symmetrical about axis
Output Impedance

• Rated at 150 ohms (90 ohms actual)
• Recommended minimum load impedance: 800 ohms
• (May be used with loads as low as 150 ohms with reduced clipping level)

Output Level (at 1,000 Hz, measured with sound source at 30° incidence to infinite surface)

• Open Circuit Voltage . . . . . . . . . . . -71.5 dB (0.27 mV)

0 dB = 1 V/μbar
Preamplifier Output Clipping Level (at 1,000 Hz, less than 0.1% THD)

• 800 ohm load . . . . . . . . . . . . . . . . . . . . . . . 0 dBV (1.0V)
• 150 ohm load . . . . . . . . . . . . . . . . . . . -13 dBV (0.22V)

Maximum SPL (at 1,000 Hz, sound source at 30° incidence to infinite surface)

• 800 ohm load . . . . . . . . . . . . . . . . . . . . . . . . . . 146.5 dB
• 150 ohm load . . . . . . . . . . . . . . . . . . . . . . . . . . 136.5 dB

Hum Pickup: -13.5 dB equivalent SPL in 1 m0e field (60 Hz)
Output Noise

• 25.5 dB SPL, A-weighted
• 28.5 dB SPL, weighted per DIN 45 405

Signal-to-Noise Ratio: 68.5 dB re 94 dB SPL
Dynamic Range: 121 dB
Phasing: Positive pressure on diaphragm produces positive voltage on pin 2 relative to pin 3 of preamplifier output connector.
Power

• Battery: Two 9-Vdc alkaline (NEDA 1604A), approximately 300 hours continuous with fresh alkaline batteries
• Simplex Voltage: 11 to 52 Vdc, operational down to 9 Vdc; 1.8 mA current drain; permissible to use simplex power with batteries in place or removed

Case:

• Microphone: Matte black enamel die-cast base and perforated steel grille with replaceable or cleanable fine mesh screen and foam pad wind/dirt barrier
• Preamplifier: Matte black enamel die-casting

Environmental Conditions

• Operating Temperature: -18° to 57°C
• Storage Temperature: -29° to 74°C
• Relative Humidity (Operating or Storage): 0 to 95%

Dimensions: 129 x 96 mm
Net Weight

• Microphone: 263 grams less cable
• Preamplifier: 435 grams less batteries