The Shure Model 51 is a dynamic pressure-type microphone with omnidirectional polar pattern, engineered for vocals, speech, instrument recording, public address systems, and communication services. A multi-impedance selector switch accommodates low (25–50 ohms), medium (150–250 ohms), and high (35,000 ohms) input impedances, eliminating the need for external matching transformers in most installations. Low-impedance operation permits practically unlimited cable lengths without response or level degradation, ideal for long runs or high-hum environments. The microphone features a chrome-plated die-cast body, self-tensioning swivel mount (0° to 80° backward), and detachable two-conductor shielded cable connector on standard 5/8″–27 thread. Model 51S variant includes an on-off switch; standard Model 51 does not.
Technical Specifications
• Type: Dynamic, pressure type
• Polar Pattern: Omnidirectional
• Frequency Response: 60 Hz to 10,000 Hz
• Output Level (1,000 Hz)
– Low Impedance (25–50 Ω): −51.0 dB (0 dB = 1 mW/10 µbar)
– Medium Impedance (150–250 Ω): −51.0 dB (0 dB = 1 mW/10 µbar)
– High Impedance (35,000 Ω): −48.5 dB (0 dB = 1 V/µbar)
• Sensitivity (1,000 Hz) per EIA SE-105 (August 1949)
– L Position (25–50 Ω): −144.0 dB ± 3 dB
– M Position (150–250 Ω): −143.0 dB ± 3 dB
– H Position (35,000 Ω): −145.0 dB ± 3 dB
• Dimensions: 115.1 mm H × 79.4 mm W × 98.4 mm D
– Key Features
• Front-mounted multi-impedance selector switch (L, M, H positions)
• Chrome-plated die-cast enclosure
• Self-tensioning swivel mount with 80° backward tilt range
• Detachable two-conductor shielded cable
• Standard 5/8″–27 mounting thread
– Compatibility & Integration
• Direct interface with 25–50 Ω, 150–250 Ω, and high-impedance inputs
• Optional Shure Model A95A Line Matching Transformer for coupling low-impedance output to high-impedance amplifiers
• Compatible stand assemblies: Model S39A (vibration isolation), Model S36A (desk stand)
• Optional isolation unit: Model A47 Quick-Disconnect
• Cable assembly: Model C55
