Shure SM81 Cardioid Instrument Condenser Microphone

Shure SM81 Cardioid Instrument Condenser Microphone

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Product Description

The Shure SM81 is a high-quality, unidirectional condenser microphone designed for studio recording, broadcasting, and sound reinforcement. Its wide frequency response, low noise characteristics, and low RF susceptibility have made it a standard for applications involving acoustic instruments, especially guitar, piano, and cymbals.

The SM81 is ruggedly constructed. It operates on phantom power and performs over a wide range of temperatures and humidity conditions. It is furnished with a swivel adapter, attenuator-switch lock, foam windscreen, and case for carrying and storage. Other accessories are available. 

  • 0 Hz to 20 kHz frequency response

  • Flat response curve for accurate reproduction of sound sources

  • Low noise and high output clipping level

  • Low distortion over a wide range of load impedances

  • Cardioid polar pattern, uniform with frequency and symmetric about axis, providing maximum rejection and minimum coloration of off-axis sounds

  • Low RF susceptibility

  • Selectable low-frequency response: flat, 6 or 18 dB/octave rolloff

  • 0 dB/10 dB lockable attenuator switch

  • Phantom powering (DIN 45 596 voltages of 12 to 48 Vdc)

  • Rugged steel construction for durability

  • Field-usable over wide range of temperature and humidity conditions


Condenser (electret bias)

Frequency Response

20 to 20,000 Hz

Polar Pattern

Cardioid (unidirectional) response-uniform with frequency, symmetrical about axis

Output Impedance

Rated at 150 ohms (85 ohms actual)

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

Output Configuration and Connector

Balanced, transformer-coupled output; male XLR connector

Sensitivity (at 1,000 Hz)

Open Circuit Voltage: -45 dBV/Pascal (5.6 mV

(1 Pascal = 94 dB SPL)

Clipping Level (at 1,000 Hz)

800 ohm Load: -4 dBV (0.63 V)

150 ohm Load: -15 dBV (0.18 V)

Total Harmonic Distortion

Less than 0.5% (131 dB SPL at 250 Hz into 800 ohm load)

Maximum SPL (at 1,000 Hz)

800 ohm load: 136 dB (attenuator at 0) 146 dB (attenuator at -10)

150 ohm load: 128 dB (attenuator at 0) 138 dB (attenuator at -10)

Hum Pickup

-3 dB equivalent SPL in a 1 mOe field (60 Hz)

Self-Noise (equivalent sound pressure levels; measured with true rms voltmeter)

16 dB typical, A-weighted

19 dB typical, weighted per DIN 45 405

Signal-to-Noise Ratio

78 dB (IEC 651)* at 94 dB SPL

*S/N ratio is difference between 94 dB SPL and product's equivalent self noise (SPL A-weighted).

Overvoltage and Reverse Polarity Protection

Max. external voltage applied to pins 2 and 3 with respect to pin 1: +52 Vdc

Reverse polarity protection: 200 mA max. (diode-clamped)


Positive pressure on diaphragm produces positive voltage on pin 2 relative to pin 3

Cartridge Capacitance

54 pF

Low Frequency Response Switch Positions

Flat; -6 dB/octave below 100 Hz; -18 dB/octave below 80 Hz

Attenuator Switch Positions (Lockable)

0 or -10 dB


Supply Voltage: 11 to 52 Vdc, positive, pins 2 and 3

Current Drain: 1.2 mA max.

Environmental Conditions


Storage: -29 degrees to 74 degrees C (-20 degrees to 165 degrees F)

Operating: -6.7 degrees to 49 degrees C (20 degrees to 120 degrees F)


Storage 0 to 95% relative humidity at room temperature (72 degrees to 80 degrees F, 22 degrees to 27 degrees C)


Steel construction with vinyl metallic paint finish and stainless steel screens


See User Guide


Net: 230 grams (8 oz)

Packaged: 740 grams (1 lb 10 oz)

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