Microphone impedance

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Paul Alexander

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Jan 16, 2023
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Hello,
Can someone clarify microphone impedance?

I have two headset mics, one with an output impedance of 150 ohms (Shure BRH31M), and another with an output impedance of <2200 ohms (J K Pro Earhook Headset Headworn Microphone MIC-J 060). I have to turn up speaker volume much more when I use the 150 ohm mic. It seems it should be the other way around, assuming the second mic has a greater resistance. Does anyone know the proper way to think about this?

Thanks!
 
The impedance spec is not the one that matters in this case.
The two mics appear to have very different sensitivity specs, which is what you're discovering.
The Shure is -66.5dB, whereas the JK Pro is -43dB.
Assuming they're measured under the same conditions, the JK will produce ~23dB more signal for the same acoustic input.
 
David Morison said:
The impedance spec is not the one that matters in this case.
The two mics appear to have very different sensitivity specs, which is what you're discovering.
The Shure is -66.5dB, whereas the JK Pro is -43dB.
Assuming they're measured under the same conditions, the JK will produce ~23dB more signal for the same acoustic input.
Click to expand...
Thanks for the reply, that is helpful.

I had a very similar question regarding two ear pieces. One of them is the same Shure BRH31M headset, while the other is Enersound EAR-101 Earphones (Mono). I am not getting signal from the Shure, but I am getting plenty of signal from the Enersound. What would be the determining factor here? The sensitivities are about the same and the impedance from the the Shure is actually less.

Thanks again!
 
I suspect that if we assume the Shure is functioning, and not faulty, then it is just wiring. Stick a test meter across them and see what it reveals.
 
Mike Caldwell said:
You must have already made up a break out cable or re terminated the Shure cable with other connectors as the Rode
units only have 3.5mm inputs.

Maybe post a picture or two.
Click to expand...
I did, but I just need to know the critical spec(s) that determine throughput (per my above message to Paul Johnson)
 
You are confusing us? What has speaker impedance go to do with this? Each mic has a nominal output voltage. Lower output equals lower level to the amp. if one mic doesn’t work, this is nothing to do with impedance matching. Almost certainly it’s to do with the polarising voltage. If you’ve been looking at the wiring, some mics have the screen and one conductor, others have a screen and two conductors. Some have audio and 5V on just a single conductor, others have the 5v separate. My guess is that somehow you have lost the 5v from where the mic expects it.

impedance is just about matching. A device is designed to work into a specific circuit impedance. You get a good or bad match. Get it wrong and you might find level gets reduced and often frequency response. In general, lower impedance sending to higher impedance inputs is better than the other way around. So a 150 Ohm mic into a 600Ohm input is not worth thinking about. An ancient 25Ohm mic into a high impedance guitar amp will probably be silence, it’s virtually a short circuit.

your silence is wiring.
 
Paul Johnson said:
You are confusing us? What has speaker impedance go to do with this? Each mic has a nominal output voltage. Lower output equals lower level to the amp. if one mic doesn’t work, this is nothing to do with impedance matching. Almost certainly it’s to do with the polarising voltage. If you’ve been looking at the wiring, some mics have the screen and one conductor, others have a screen and two conductors. Some have audio and 5V on just a single conductor, others have the 5v separate. My guess is that somehow you have lost the 5v from where the mic expects it.

impedance is just about matching. A device is designed to work into a specific circuit impedance. You get a good or bad match. Get it wrong and you might find level gets reduced and often frequency response. In general, lower impedance sending to higher impedance inputs is better than the other way around. So a 150 Ohm mic into a 600Ohm input is not worth thinking about. An ancient 25Ohm mic into a high impedance guitar amp will probably be silence, it’s virtually a short circuit.

your silence is wiring.
Click to expand...
My apologies for the confusion. David Morrison had answered my initial question regarding the mic, so I was asking a second one regarding two different speakers with the same audio input. Thanks for the reply.
 
With these things, differences in the speakers are like mics, sensitivity and impedance. However, the key factor is what you drive them with. 8 ohms or 16 ohms means that a knob setting of say half on the 8 ohm earpieces will be a bit quieter on the 16 ohm ones, so you turn up a bit. If you reach full and its not loud enough, you’re stuck!
 
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