Hi, can anyone tell me what Impedance and sensitivity mean when talking about a mic please? say an impedance of 1k and sensitivity of 65dB?
Thanks in advance for taking time out for this newbie me!
The sensitivity of a microphone states what RMS AC voltage it delivers out when exposed to a standarized sound pressure level. The sound pressure used by the industry is 1 Pascal. "94 dB SPL" is defined to be 1 Pascal. This SPL must be present at the location of the diaphragm. The test is done at a frequency of 1000 Hz.
Typically condencer mics deliver -40 dB (or 0.01 Volts RMS) re 1V @ 94 dB SPL at 1kHz.
At 114 dB SPL the mic then delivers 20 dB more or 0.1 Volts RMS
At 134 dB SPL, assuming the mic output scales linearily with SPL, you find 1 Volt RMS on the output.
A sensitivity of -65 dB re 1 Volts/94 dB SPL @ 1k Hz, IF correct, means you get 0.0007 Volts RMS when subjecting the mic to 94 dB SPL. This mic needs some serious gain stages before the signal can be sent to the ADC stage. Maybe the number stated is confused with the dynamic range?
The impedance stated can either be the internal source impedance or the minimum recommended load impedance. The number stated is ballpark correct for the internal resistance of cheap electrets. The external load impedance should be 5 times higher or more. This help prevent loss of output voltage due to the output current having to flow through the internal series resistor.
Jon