Shure SM94 User Manual
MODEL SM94
UNIDIRECTIONAL CONDENSER MICROPHONE
The Model SM94 is a unidirectional electret condenser
microphone tailored to the instrument miking needs of professional
musicians and sound engineers in both live performance and
sound recording. Its smooth, flat frequency response is free of
either a “presence peak” or a low-frequency rolloff, making it a
perfect choice for all types of musical instruments. The SM94 is
equally at home in sound reinforcement systems or in sound
studios and motion picture/TV scoring stages. When used with the
optional windscreen, the SM94 can be used by vocalists and
speechmakers who desire a wide, flat response with minimum
coloration.
The SM94 can be powered by any phantom power source, or by
an internal 1.5-volt AA battery. The battery, which serves as a
backup power source in the event of phantom power failure, can
provide up to 5,000 hours of continuous operation.
The SM94 is supplied with a swivel adapter for use on a
microphone stand, boom or gooseneck, and a zippered vinyl
storage bag. Model SM94-LC is supplied without a cable.
Accessories include a foam windscreen (A3WS), two-channel
phantom power supply (PS1A), and 7.6 m (25 ft.) microphone
cable (C25J).
Model SM94 User Guide
• Accepts 12 to 48 Vdc phantom power
• Rugged all–metal construction
• Usable over wide range of environmental conditions
• Built–in battery power backup
• Optional foam windscreen
SPECIFICATIONS
Type
Cardioid condenser (electret bias)
Frequency Response
40 to 16,000 Hz (see Figure 1)
TYPICAL FREQUENCY RESPONSE
FIGURE 1
Polar Pattern
Cardioid (unidirectional)–uniform with frequency,
symmetrical about axis (see Figure 2)
Features
• Wide, flat response for optimum musical instrument sound reproduction
• Full spectrum sound–no presence peak or low-end rolloff
• Cardioid polar pattern that is uniform with frequency and symmetrical about axis for maximum rejection of unwanted sound
and minimum of-axis coloration
• Very low susceptibility to RF and electromagnetic hum
• Low distortion output and wide dynamic range for variety of load
impedances
• Shock–mounted cartridge for reduced handling noise
©2005, Shure Incorporated
27C2689 (Rev. 5)
TYPICAL POLAR PATTERNS
FIGURE 2
Printed in U.S.A.
Output Impedance
Rated at 150 Ω; 200 Ω actual
Recommended Minimum Load Impedance
800 Ω
Sensitivity (at 1,000 Hz)
Open Circuit Voltage: –49 dBV/Pa (3.5 mV) (phantom)
–50 dBV/Pa (3.2 mV) (battery) (1 Pa = 94dB SPL)
Output Clipping Level (1 kHz, 3% THD)
800-Ω Load–14 dBV (0.63 V) (phantom), 1% THD;
–23 dBV (0.71 V) (battery), 3% THD
Total Harmonic Distortion
< 0.25% (130 dB SPL at 250 Hz into 800 Ω load)
Maximum SPL
800 Ω Load: 141 dB (phantom), 123 dB (battery)
Hum Pickup
–3 dB equivalent SPL in a 1 millioersted field (60 Hz)
Output Noise (equivalent sound pressure levels;
measured with true rms voltmeter)
22 dB typical, A-weighted
25 dB typical, weighted per DIN 45 505
Dynamic Range
119 dB (phantom); 101 dB (battery) (maximum SPL,
2000–Ω load, to A–weighted noise level)
Signal-to-Noise Ratio
72 dB (IEC 651)* at 94 dB SPL
Overvoltage Protection
Maximum External Voltage Applied to Pins 2 and 3
with respect to Pin 1: +52Vdc
Reverse polarity protected to 75 Vdc
Polarity
Positive pressure on diaphragm produces positive
voltage on pin 2 relative to pin 3
Cartridge Capacitance
24 pF
Power
Phantom Operation
Supply Voltage: 11 to 52 Vdc, (+) pins 2 and 3
Current Drain: 1.0 to 1.2 mA max. at 52 Vdc
Battery Operation
Type: 1.5 V alkaline, AA size (NEDA 15A)
Life: Up to 5,000 hours with fresh battery
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)
Connector
XLR professional audio 3-Pin
Case
Steel and brass construction with gray finish and
stainless steel mesh grille
Dimensions
See Figure 3
OVERALL DIMENSIONS
FIGURE 3
Weight
Net 250 grams (8.8 oz) less battery
Packaged SM94-LC: 949.7 grams (2 Ib 1 1/2 oz)
Certification
Eligible to bear CE Marking. Conforms to European EMC Directive
89/336/EEC. Meets applicable tests and performance criteria in
European Standard EN55103 (1996) parts 1 and 2, for residential
(E1) and light industrial (E2) environments.
*S/N ratio is difference between microphone output at 94 dB SPL and
microphone self-noise A-weighted.
OPERATION
The SM94 is designed for phantom powering by a Shure PS1A
Power Supply, or by any microphone power supply providing 12 to
48 Vdc phantom voltage, or by any microphone mixer (such as the
Shure SCM262 and SCM268) with a phantom supply. In addition,
the SM94 can be powered by a single 1.5-volt AA alkaline battery.
The battery also serves as a backup in case of phantom power
failure. A new alkaline battery will provide up to 5,000 hours of
continuous microphone operation. Note that the microphone is
powered at all times during battery operation but there is no battery
drain during phantom-powered operation.
BATTERY OPERATION
Disconnect the microphone cable, and unscrew the SM94 handle,
turning counterclockwise (from top) until the handle is free of the
microphone body. Slide the handle away from the grille, exposing
the battery compartment. Insert a new battery (or replace the old
battery), observing the polarity marking in the compartment.
Slide the handle toward the grille, and tighten the handle by turning
it clockwise (from top).
WIND NOISE
Use the optional foam windscreen (A3WS) when using the SM94
outdoors on a windy day, indoors near strong air currents such as
air-moving equipment, or as a vocal microphone.
CIRCUIT DESCRIPTION
A block diagram of the SM94 is shown in Figure 4. The capacitor
cartridge is followed by an impedance converter stage. This stage
has an active load to obtain good load-driving capability with the
low battery voltage of 1.5 volts.
The audio signal is transformer-coupled for a balanced output to
the microphone connector. An active power supply circuit
2
regulates the phantom voltage, and the 1.5-volt battery provides
instantaneous backup in case the phantom power supply fails. The
regulator/reverse voltage protector provides built-in protection
against miswired cables and equipment.
TROUBLESHOOTING
Due to the circuit complexity of the SM94, only basic servicing is
recommended. The following steps should be taken if problems
arise:
1. Check the power supply output voltage. For the Shure PS1A,
this should be 21.5, ±1.5 Vdc, open circuit.
2. Check the voltage on connector pins 2 and 3 (at back of
connector, with cable connector removed from shell, but
connected to microphone). The voltage at pins 2 and 3 with
reference to pin 1 should be between 10 and 48 Vdc.
3. If the microphone does not work on phantom power, battery
operation may still be possible. Similarly, if battery operation is
impaired, the SM94 may still operate on phantom power. In
either case, you should send the microphone to an Authorized
Shure Service Center at your earliest opportunity.
ARCHITECTS' SPECIFICATIONS
The microphone shall be a condenser microphone with a
frequency response of 40 to 16,000 Hz. It shall have a cardioid
directional characteristic, with cancellation at the sides of 6 dB and
a minimum cancellation at the rear of 15 dB at 1 kHz. The
microphone shall have a rated output impedance of 150 Ω for
connection to microphone inputs of 150 Ω or higher. The open
circuit voltage shall be –49 dBV/Pa (3.5 mV) dB equals 1 volt per
Pascal).
The overall dimensions shall be 190.5 mm (7–1/2 in.) in length by
27.7 mm (1–3/32 in.) in diameter. The handle diameter shall be
24.1 mm (15/16 in.) The weight shall be 250 grams (8.8 oz).
The microphone shall be capable of being powered by a phantom
power supply with an output of 11 to 52 Vdc, or by a mixer, audio
console or tape recorder capable of supplying 11 to 52 Vdc, or by
an internal 1.5-volt battery.
The microphone shall be a Shure Model SM94.
FURNISHED ACCESSORIES
Swivel Adapter .................................................................. A25D
Carrying/Storage Bag ...................................................... 26A13
OPTIONAL ACCESSORIES
Phantom Power Supply.................................................... PS1A
Switch-Selectable Attenuator ........................................ A15AS
Isolation Mount .................................................................A53M
Windscreen ..................................................................... A3WS
7.6 m (25 ft.) Cable .......................................................... C25J
CAPACITOR
CARTRIDGE
IMPEDANCE CONVERTER
FET
WITH ACTIVE LOAD
BATTERY
LF RESPONSE
FILTER
BLOCK DIAGRAM
FIGURE 4
REPLACEMENT PARTS
Screen and Grille ......................................................... RK255G
BALANCED
TRANSFORMER
CLASS A
COMPOUND
AMPLIFIER
RFI
FILTER
REGULATOR/
REVERSE VOLTAGE
PROTECTOR
3
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