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
Certification
Eligible to bear CE marking. Conforms to European EMC Directive 89/336/EEC. Meets applicable tests and performance criteria in European EMC Standard EN 55103 (1996) parts 1 and 2 for residential (E1) and light industrial (E2) environments.
Signal-to-Noise Ratio
78 dB (IEC 651)* at 94 dB SPL
*S/N ratio is difference between microphone output at 94 dB SPL and microphone self-noise A-weighted.
OPERATION
Power
The SM81 requires phantom power. This may be supplied to the microphone by a mixer, preamplifier or console with builtin phantom power or from an external power supply (such as the Shure model PS1A). Phantom power sources providing between 11 and 52 Vdc are suitable. Use only high-quality cables because intermittent shorts between broken shield wires and balanced conductors will cause extremely large noise transients in the system. Avoid ground loops due to grounded connector shells or the microphone case touching other grounded metal objects. Follow generally accepted audio grounding practices.
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)
Polarity
Positive pressure on diaphragm produces positive voltage on pin 2 relative to pin 3
Cartridge Capacitance
54 pF
Impedance
A minimum load impedance of 800 � or greater should be used for maximum signal handling and minimum distortion. The load may be as low as 150 �, but a reduction in output clipping level will result. It should be noted that the power supply itself may add loading (3300 � in the Shure PS1A power supply) to the microphones.
Attenuator Switch Positions (Lockable)
0 or �10 dB
Power
Supply Voltage . . 11 to 52 Vdc, positive, pins 2 and 3 Current Drain . . . . . . . . . . . . . . . . . . . . . . . . 1.2 mA max.
PS1A Power Supply
When using the Shure PS1A to phantom power the SM81, connect the microphone cable to the SM81 and to the MICROPHONE connector of the power supply. The power supply uses the balanced audio cable pair to carry the supply current to the microphone and the cable shield as a ground return. Connect the OUTPUT connector of the power supply to a low-impedance microphone input of a mixer, audio console or tape recorder. A second SM81 may be connected to the remaining power supply channel in a similar manner.
Environmental Conditions
Temperature: Storage . . . . . . . . . . . . . . . . . . . . . . . . � 29_ to 74_ C (�20_ to 165_ F) Operating . . . . . . . . . . . . . . . . . . . . . . � 6.7_ to 49_ C (20_ to 120_ F) Humidity: Storage . . . . . . . . . 0�95% relative humidity at room temperature (72_to 80_ F, 22_ to 27_ C)
Case
Steel construction with vinyl metallic paint finish and stainless steel screens
