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# Microphones and Acoustics

Section I: Definitions and Terminology
Section II: Microphone Recommendations
Section III: Calibration and Testing
Section IV: Specification Clarifications
Section V: Specialty Microphone Applications
Section VI: Maintenance and Handling

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Why is the output of my prepolarized microphone 180 degrees out of phase with my externally polarized microphone?

When positive pressure is exerted on a prepolarized (0V) microphone, it will send a positive output voltage to a voltmeter or data acquisition (DAQ) system. When positive pressure is exerted on an externally polarized (200V) microphone, it will output a negative voltage to the DAQ. The outputs are 180 degrees out of phase between prepolarized and externally polarized microphones.

Externally polarized microphones have positive 200 volts applied directly to the backplate. Prepolarized microphones use an electret which stores a permanent electrical charge on a polymer on the backplate of the microphone with an equivalent of negative 200 volts embedded into the electret on the backplate.

When externally and prepolarized microphones are exposed to the same acoustic stimuli, they will have opposite phases. The equivalent voltage of a prepolarized microphone is -200 volts and external polarization is +200V. Positive pressure on the diaphragm creates a negative output voltage for externally polarized microphones and a positive output voltage for prepolarized microphones.

This diagram shows two microphones with the same 1 volt output. This illustrates a prepolarized microphone vs. externally polarized microphone outputs that is out of phase 180 degrees.

When similar sensitivity prepolarized and externally polarized microphones are subjected to the same sound pressure level, the voltage output will be the same in amplitude and opposite in phase.

Why is the output of my prepolarized microphone 180 degrees out of phase with my externally polarized microphone?

When positive pressure is exerted on a prepolarized (0V) microphone, it will send a positive output voltage to a voltmeter or data acquisition (DAQ) system. When positive pressure is exerted on an externally polarized (200V) microphone, it will output a negative voltage to the DAQ. The outputs are 180 degrees out of phase between prepolarized and externally polarized microphones.

Externally polarized microphones have positive 200 volts applied directly to the backplate. Prepolarized microphones use an electret which stores a permanent electrical charge on a polymer on the backplate of the microphone with an equivalent of negative 200 volts embedded into the electret on the backplate.

When externally and prepolarized microphones are exposed to the same acoustic stimuli, they will have opposite phases. The equivalent voltage of a prepolarized microphone is -200 volts and external polarization is +200V. Positive pressure on the diaphragm creates a negative output voltage for externally polarized microphones and a positive output voltage for prepolarized microphones.

This diagram shows two microphones with the same 1 volt output. This illustrates a prepolarized microphone vs. externally polarized microphone outputs that is out of phase 180 degrees.

When similar sensitivity prepolarized and externally polarized microphones are subjected to the same sound pressure level, the voltage output will be the same in amplitude and opposite in phase.