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Microphone Output Impedance

 

Here's the link, in case anyone is looking:?
/g/MicBuilders/files/Microphone%20impedance%20test%20jig%20Model.pdf
 

Dear Jerry,?

I don't understand you impedance test jig.
?
Microphone connect to pre-amp input ?
after, measure pre-amp output ?
?
Where should the audio analyzer be positioned?
The signal generator is located at the microphone and preamp, but I am unsure where the audio analyzer,
which will be used to measure sensitivity changes, should be placed.
?
I believe the signal injection model is probably similar to the impedance measurement method of the MR-PRO.
?
thanks to Jerry,
Best Regards,
?
Kandoit7
 

Le 21/12/2024 à 12:56, kandoit7 via groups.io a écrit?:
Dear Jerry,

I don't understand you impedance test jig.
Microphone connect to pre-amp input ?
Yes
after, measure pre-amp output ?
Yes
Where should the audio analyzer be positioned?
At the output of the mic preamp.
The signal generator is located at the microphone and preamp, but I am unsure where the audio analyzer,
which will be used to measure sensitivity changes, should be placed.
As I just daid.
I believe the signal injection model is probably similar to the impedance measurement method of the MR-PRO.
Somewhat but not exactly.
 

?
Dear Jerry,
?
Hello. In the meantime, my answer was late because I was preparing for the experimental environment.
?
I made it with reference to the circuit diagram you gave me. I just changed the resistance of R1 and R2 to potentiometer.
?
?
Generator? ? : NTi Audio MR-PRO
Microphone : Earthworks M23R
Preamp? ? ? ?: RME OctaMIC II
Analyzer? ? ? : NTi Audio Fx100
?
A value measured without a resistance connection.
?
?
It is a value that is later reduced by 6 dB.
?
?
At this point, the value of the resistance is
R1 : 69.5 Ohm
R2 : 66.8 Ohm .
?
The specific of the M23R provided on the homepage is 65Ω balanced (between pins 2 & 3).
?
I think there is an error in the result value, but is it normal that the values of R1 and R2 are originally similar?
?
And it seems that M23R product is not balanced. When M23R is connected directly to MR-PRO, the R value for pin 2 is:86 Ohm, and the R value for pin 3 is:260 Ohm. For normal balanced microphone, the resistance values for pin 2 and pin 3 are the same.
Even in this situation, I wonder if the above measurement method can be applied.
?
I would like to know your thoughts based on this result.
?
I'm currently looking for a reliable microphone to measure other microphones.
I'll show you the results as soon as it goes.
?
Thank you.
?
I'm late to say hello, but happy new year.
?
Best Regards,
Kandoit7
 

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Actually, the wiring should be that:


Make sure that nothing is connected to Pin1 of minirator.


Le 24/01/2025 à 03:52, kandoit7 via groups.io a écrit?:

?
Dear Jerry,
?
Hello. In the meantime, my answer was late because I was preparing for the experimental environment.
?
I made it with reference to the circuit diagram you gave me. I just changed the resistance of R1 and R2 to potentiometer.
?
?
Generator? ? : NTi Audio MR-PRO
Microphone : Earthworks M23R
Preamp? ? ? ?: RME OctaMIC II
Analyzer? ? ? : NTi Audio Fx100
?
A value measured without a resistance connection.
?
?
It is a value that is later reduced by 6 dB.
?
?
At this point, the value of the resistance is
R1 : 69.5 Ohm
R2 : 66.8 Ohm .
?
The specific of the M23R provided on the homepage is 65Ω balanced (between pins 2 & 3).
?
I think there is an error in the result value, but is it normal that the values of R1 and R2 are originally similar?
?
And it seems that M23R product is not balanced. When M23R is connected directly to MR-PRO, the R value for pin 2 is:86 Ohm, and the R value for pin 3 is:260 Ohm. For normal balanced microphone, the resistance values for pin 2 and pin 3 are the same.
Even in this situation, I wonder if the above measurement method can be applied.
?
I would like to know your thoughts based on this result.
?
I'm currently looking for a reliable microphone to measure other microphones.
I'll show you the results as soon as it goes.
?
Thank you.
?
I'm late to say hello, but happy new year.
?
Best Regards,
Kandoit7
 

?
Actually
?
MR-PRO ->? potentiometer? ->? ?Mic? -> Preamp
Pin 1? ? ? ?->? ? ? ? ? ?GND? ? ? ? ? ->? ?GND -> GND
Pin 2? ? ? ?->? ? ? ? ? ? ?R1? ? ? ? ? ? ->
Pin 3? ? ? ?->? ? ? ? ? ? ?R2? ? ? ? ? ? ->
?
?
MR-PRO Pin 1 connect GND.
?
Should I disconnect pin 1 of the MR-PRO?
 

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Le 25/01/2025 à 01:16, kandoit7 via groups.io a écrit?:
?
Actually
?
MR-PRO ->? potentiometer? ->? ?Mic? -> Preamp
Pin 1? ? ? ?->? ? ? ? ? ?GND? ? ? ? ? ->? ?GND -> GND
Pin 2? ? ? ?->? ? ? ? ? ? ?R1? ? ? ? ? ? ->
Pin 3? ? ? ?->? ? ? ? ? ? ?R2? ? ? ? ? ? ->
?
?
MR-PRO Pin 1 connect GND.
?
Should I disconnect pin 1 of the MR-PRO?
Yes.
 

Dear Jerry,
?
I’m still getting similar results.
R1 : 66 Ohm
R2 : 65 Ohm

Here’s my question:
I’m using a single potentiometer to control both channels (R1 and R2), meaning adjusting it changes both values to nearly the same resistance.
?
Should I instead use separate potentiometers for R1 and R2 to adjust them independently?
?
This comes up because when I directly connected the M23R to the MR-PRO, the microphone’s impedance measurements showed imbalance.?
?
Best Regards,?
Kandoit7
 

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It seems correct, indicating a mic impedance of about 130 ohms.

Le 02/02/2025 à 06:25, kandoit7 via groups.io a écrit?:

Dear Jerry,
?
I’m still getting similar results.
R1 : 66 Ohm
R2 : 65 Ohm

Here’s my question:
I’m using a single potentiometer to control both channels (R1 and R2), meaning adjusting it changes both values to nearly the same resistance.
?
Should I instead use separate potentiometers for R1 and R2 to adjust them independently?
?
This comes up because when I directly connected the M23R to the MR-PRO, the microphone’s impedance measurements showed imbalance.?
?
Best Regards,?
Kandoit7
 

Dear Jerry,?
?
Thanks to your reply.
?
Earthworks Homepage's M23R Spec :
?
OUTPUT IMPEDANCE ? ?65Ω balanced (between pins 2 & 3)
?
This is the specification provided on the website.

What I mean here is not the Symmetric impedance between Pin 2 and Pin 3?
I think R1 + R2 = Symmetric impedance.
?
If so, 130 Ohm would be the output impedance, but I wonder if Earthworks is providing 65 Ohm.
?
haha, Thanks to you, I am building up my knowledge.
?
Best Regards,
Kandoit7
 

"Earthworks Homepage's M23R Spec :
OUTPUT IMPEDANCE ? ?65Ω balanced (between pins 2 & 3)"
?
That means exactly what it states, that the output signal is taken between pins 2 and 3, and the impedance of that signal is 65 Ohms.? Very likely not a transformer output, so an active output would have common mode impedances of 32.5 Ohms from pin 2 referenced to pin 1, and also from pin 3 referenced to pin 1, but for a transformer coupled output there would be no galvanic connection between either pin 2 or 3 and pin 1, so it would not make sense to discuss the impedance of pin 2 separately from pin 3, except in the context of parasitic capacitance and how that affects high frequency common mode impedance.
?
-- Chris C

?
 

On Wed, Dec 18, 2024 at 08:02 AM, kandoit7 wrote:
In the case of measuring condenser microphone impedance using voltage drop
Try this method shown in a Jensen Tranformer app-note:
?
That will work for an active output microphone if you measure the impedance of pin 2 reference to pin 1, and separately pin 3 referenced to pin 1, and add the results together.
For a transformer output microphone you would use pin 3 as the reference pin for the signal generator, and connect the measurement resistor to pin 2.
?
-- Chris C
 

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Le 04/02/2025 à 00:06, Chris Caudle via groups.io a écrit?:
On Wed, Dec 18, 2024 at 08:02 AM, kandoit7 wrote:
In the case of measuring condenser microphone impedance using voltage drop
Try this method shown in a Jensen Tranformer app-note:
This method is valid for unbalanced loads, but not for all types of balanced loads..
?
That will work for an active output microphone if you measure the impedance of pin 2 reference to pin 1, and separately pin 3 referenced to pin 1, and add the results together.
This is true only if the outputs are non-floating, which is the case of the typical Schoeps arrangement, or impedance-balanced circuits.
Some circuits need to be measured differentially.
For a transformer output microphone you would use pin 3 as the reference pin for the signal generator, and connect the measurement resistor to pin 2.

That is correct for a xfmr output, but electronically balanced circuits may not be suitale for having one of their legs grounded.

That's why I recommended the OP to use a fully floating measurement system.

?
-- Chris C

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