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UNIDYNE
®
III MODEL 545SD
User Guide
©2005, Shure Incorporated
27D3059 (Rev. 10)
Printed in U.S.A.
GENERAL
The UNlDYNE
®
III Model 545SD is a dual-impedance, unidirectional,
dynamic microphone. Shipped connected for low-impedance opera-
tion, it features a silent magnetic reed on/off switch.
The UNlDYNE III is a favorite for instrument pickup and recording,
and can be used on lecterns for public address systems such as
those used in political conventions and legislatures, convention
halls, hotels, public auditoriums, stadiums, schools, and churches.
FEATURES
• Exceptionally uniform cardioid pattern minimizes feedback in
PA applications
• Selectable dual-impedance operation
• Silent magnetic reed on/off switch with lock option
• Cardioid dynamic
• Frequency response: 50 to 15,000 Hz
CONNECTIONS
when using the microphone with a balanced input, pins 2 and 3 are
the audio signal carriers. When using the microphone with an
unbalanced input, use a cable wired with pin 2 as the signal carrier
and pin 3 connected to the cable shield (ground), such as the
Shure C20HZ high-impedance cable.
IMPEDANCE SELECTION
The microphone is shipped connected for low impedance
operation. To change to high impedance, proceed as follows (refer
to Figure 1):
1. Remove plug element at receptacle end of microphone by
turning slotted setscrew in (counterclockwise) and carefully
withdrawing plug element from case.
2. Disconnect 2–terminal impedance selection socket from rear
of plug element.
3. Reconnect 2–terminal impedance selection socket in reverse
position so that pin 3 of plug element is inserted in socket ter-
minal “H” (White).
4. Reassemble plug element into microphone and seal setscrew
securely by turning out (clockwise).
IMPEDANCE SELECTION-
RECEPTACLE END OF MICROPHONE
FIGURE 1
POLARITY
All cables and microphones should be tested to ensure that they
have the same polarity. To test two microphones and/or their
cables for proper polarity, connect them to an amplifier and talk or
sing into them while holding them three or four inches apart. The
sound from the speakers should be the same when talking into
either microphone or directly between them. If the sound drops
drastically, or if a dead spot is found when talking between the two
microphones, either the microphones or their cables have opposite
polarity.
To change the polarity of a microphone cable, either use a Shure
A15PRS phase reverser or interchange the wires connected to
pins 2 and 3 of the three-pin connector at one end of the cable. To
change the polarity of a microphone, the microphone cartridge
leads must be interchanged. This should be performed by your
dealer, the Shure Factory Service Department, or other qualified
service personnel.
SPECIFICATIONS
Type
Dynamic
Frequency Response
50 to 15,000 Hz (see Figure 2)
Polar Pattern
Cardioid (unidirectional)-uniform with frequency, symmetrical
about axis (see Figure 3)
lmpedance
Dual. Microphone rating impedance is 150 ohms (250 ohms ac-
tual) for connection to microphone inputs rated at 19 to 300
ohms and “High” for connection to high-impedance microphone
inputs.
Wired for low impedance as supplied. To change impedance,
see sections on lmpedance Selection and Connections.
Output Level (at 1,000 Hz)
“L”
“H”
Open Circuit Voltage* -58.0 dB -35.0 dB
(1.3 mV) (17.6 mV)
*0 dB = 1 volt per Pascal (1 Pa = 94 dB SPL)
SET SCREW
PLUG ELEMENT
IMPEDANCE SELECTION SOCKET
PIN 3