Classic Unidyne™ Instrument Microphone
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Shure Incorporated
Mac & Win
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The predecessor to the SM57, The 545SD Classic Unidyne™ Instrument Microphone is a dual-impedance, unidirectional, dynamic microphone.


Shipped connected for low-impedance operation, the 545SD features a silent magnetic reed on/off switch with lock-on option. A favorite for instrument pickup and recording, the 545SD can also be used on lecterns in public address systems.

The classic 545SD Unidyne® remains popular due to its smooth cardioid response and unparalleled dependability. Its lockable, silent magnetic reed on/off switch makes it ideal for unattended sound systems.

Uniform cardioid pattern

Selectable dual-impedance operation

Lockable on/off switch




Frequency Response

50 to 15,000 Hz


Polar Pattern

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



Dual. Microphone rating impedance is 150 ohms (250 ohmsactual) for connection to microphone inputs rated at 19 to 300 ohms and"High" for connection to high-impedance microphone inputs. Wired forlow impedance as supplied. To change impedance, see sections on lmpedanceSelection and Connections in User Guide.


Output Level (at 1,000 Hz)

LOW: Open Circuit Voltage* -58.0 dB (1.3 mV)

HIGH: Open Circuit Voltage* -35.0 dB (17.6 mV)

*0 dB = 1 volt per Pascal (1 Pa = 94 dB SPL)



Positive pressure on diaphragm produces positive voltage onpin 2 (with respect to pin 3).



Built-in magnetic reed on/off switch with lockplate.


Cartridge Shock Mount

Internal rubber vibration-isolator Swivel Adapter

Positive action, adjustable through 90 degrees from verticalto horizontal, permits easy removal for handheld use, suitable for mounting onstand with 5/8"- 27 thread



Chrome-plated die casting with ARMO-DUR grille andstainless steel screen


Net Weight (less cable)

255 grams (9 oz)

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