Shure sm81 user guide
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Extracted text from shure sm81 user guide (Ocr-read)
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2 Maximum SPL (at 1,000 Hz) 800 Ω load: . . . . . . . . . . . . . . . . . . . . . 136 dB (attenuator at 0) 146 dB (attenuator at -10) 150 Ω 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 microphone output at 94 dB SPL and microphone self-noise 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) Polarity 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 Power Supply Voltage:. . . . . . . . . 11 to 52 Vdc, positive, pins 2 and 3 Current Drain: . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 mA max. 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 screensDimensions See Figure 3 Weight Net: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 grams (8 oz) Packaged: . . . . . . . . . . . . . . . . . . . . . . . 740 grams (1 lb 10 oz) Certification Eligible to bear CE marking. Conforms to European EMC Direc- tive 89/336/EEC. Meets applicable tests and performance cri- teria in European EMC Standard EN 55103 (1996) parts 1 and 2 for residential (E1) and light industrial (E2) environments. OPERATION Power The SM81 requires phantom power. This may be supplied to the microphone by a mixer, preamplifier or console with built-in phan- tom 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 be- tween broken shield wires and balanced conductors will cause ex- tremely 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. Impedance A minimum load impedance of 800 Ω or greater should be used for maximum signal handling and minimum distortion. The load may be as low as 150 Ω, but a reduction in output clipping level will result. It should be noted that the power supply itself may add load- ing (3300 Ω in the Shure PS1A power supply) to the microphones. PS1A Power Supply When using the Shure PS1A to phantom power the SM81, con- nect the microphone cable to the SM81 and to the MICROPHONE connector of the power supply. The power supply uses the bal- anced audio cable pair to carry the supply current to the micro- phone 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 pow- er supply channel in a similar manner. OVERALL DIMENSIONS FIGURE 3 212 mm 20 mm 23.5 mm
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3 Low-Frequency Response Filter The SM81 has a three-position low-frequency response filter controlled by a switch located on its handle. The switch is recessed to avoid accidental movement, but may be easily moved with fin- gertips. The user may select either flat response, low-frequency rolloff of 6 dB per octave below 100 Hz, or low-frequency cutoff of 18 dB per octave below 80 Hz (see Figure 4 ). When close-miking instruments or vocalists, an increase in low-frequency response (proximity effect) takes place. Figure 4 illustrates this effect with the switch in each of the three positions. Note that the low-frequency response filter may be used to compensate for proximity effect or reduce low-frequency noise from stage traffic and other sources. PROXIMITY EFFECT AND COMPENSATION FIGURE 4 Attenuator Switch The SM81 has a switchable 10 dB capacitive attenuator to pre- vent high sound pressure levels from overloading its internal elec- tronics. The attenuator is engaged by rotating the actuator ring, located directly below the grille assembly, until it reaches the -10" position. This reduces the output of the microphone by 10 dB and increases the maximum sound pressure level at clipping by 10 dB. There are no intermediate levels of attenuation available. The attenuator ring may be locked in either the 0" or -10" po- sition as follows. Unscrew the grille and cartridge assembly by un- screwing counter-clockwise from the top. Turn the actuator ring to the 0" or -10" position as desired. Insert the actuator ring lock (small clear piece of plastic) in the area behind the actuator ring be- tween the pin and the edge of the slot. This will prevent the ring from turning. Replace the grill and cartridge assembly. Mixer Overload The SM81's output is about 15 dB higher than most dynamic mi- crophones. At moderate to high SPLs, this additional output may require attenuation (or padding). If no attenuation is available on the preamplifier, mixer or console being used, a resistive attenua- tor can be inserted between the microphone and the input. The Shure Model A15AS Attenuator (15, 20, or 25 dB switch-select- able) is specially designed for use with condenser microphones such as the SM81. Alternately, the attenuator design shown in Fig- ure 5 may be used. The resistors shown are 1/2-watt, 1% toler- ance, and the circuit may be packaged in a Switchcraft S3FM adapter housing. The circuit will provide15 dB of attenuation and can be used between the SM81 and the PS1A (or other power sup- ply), or between the PS1A and the mixer. Two of these circuits may be used in series to provide 30 dB of attenuation. (Note that, due to excessive loading, commercially available 150 Ω attenuators, such as the Shure Model A15AS, are not recommended when two are used in series.) 15 DB ATTENUATOR CIRCUIT FIGURE 5 Wind Noise The wide frequency response of the SM81 makes it sensitive to wind, breath, and air currents from heating, ventilation and cooling (HVAC) systems. The foam windscreen included with the SM81 can be used to reduce wind and breath noise, while the low-fre- quency response filter can be used to reduce low-frequency room noise caused by HVAC systems. The Model A81G Pop Filter Grille attenuates breath popping sounds when the microphone is close-talked, and permits its use outdoors with minimal pickup of rushing and rumbling sounds. To install the A81G, slip it over the SM81 until the inside of the A81G touches the top of the microphone. Tighten the A81G by rotating the knurled collar clockwise from the bottom. (Note: When remov- ing the A81G, first loosen the knurled collar. Otherwise the car- tridge will unscrew with the A81G.) For outdoor use under very windy conditions, use the Model A81WS large foam windscreen. 20 100050 100 +10 0 –10 Hz dB 152.4 MM ( ) 152.4 MM ( ) 152.4 MM ( ) 1 2 3 1 2 3 412 412215 OUTPUT TO MIXER INPUT FROM MICROPHONE