Le 19/12/2024 à 03:48, kandoit7 via groups.io a écrit?:
Your response is very helpful to me.
Complexity is not an issue when it comes to learning.
If we can derive the correct results, we should endure it. Haha
1. In the case of dynamic microphones, I think impedance measurement will be easier than other types of microphones due to the connection between pin 2 and pin 3.
2. Balanced active microphone - This is the result I'm currently trying to achieve.
In a situation where two pins have opposite polarity but supply the signal equally,
This is not mandatory for a connection to qualify as balanced.
The condition for being balanced is that both in-phase (hot) and out-of-phase (cold) pins present the same Common Mode impedance, i.e. teh impedance measured from pin 2 to pin 1 is equal to the impedance measured between pin 3 and Pin 1.
This common-mode impedance is almost never specified by manufacturers. It is wildly variable, nominally infinite for dynamic/ribbon mics, a few kiloohms for phantom powered mics. It is not specified because it's not a performance indicator.
I'm wondering whether the output impedance should be defined as the impedance between pin 2 and pin 3,
or the impedance between the output going out of pin 2 and ground.
The former.
From my personal perspective, when thinking about output, I believe the latter is correct.
Wrong.
However, as Jerry mentioned, I can't rule out the possibility that it might be the impedance between pin 2 and pin 3.
You's better.
But then again, I think there might be about a 2-fold difference between the former and the latter (in the case of balanced active microphones).
Yes, one is the output impedance (what you're endevouring to assess), the other is teh common-mode impedance, which you are probably not interested in.
There's a lot of information about sensitivity, frequency response, and polar patterns when it comes to microphone measurements.
However, I couldn't find definitive information about impedance measurement.
Impedance measurement is well documented in signal processing. Microphones are not an exception to teh general case.
I'm really curious about what method microphone manufacturers are using to measure the impedance values they provide.
There are several ways of measuring impedance at the design stage, either an impedance analyzer or the quite common method of injecting a known AC current and measuring the resulting voltage. Once the assessment has been made, the designers assign a nominal impedance, which is what the mktg dept uses for publication.
There is no need for QC'ing the output impedance, since it it is governed by design.
Note that impedance varies significantly with frequency. The published value is a mix between the average measured value and whatever the mktg dept deems acceptable.
I have measured a number of dynamic mics, uwing an impedance bridge, which is easy because they don't need to be applied phantom power.
For example, the Shure SM58 measures at 300 ohms at 1kHz and 470 ohms at 140 Hz, although it's specified as 150 ohms!
Conversely, the SM7B, rated at 150 ohms, measures 140 ohms at 1kHz and 240 ohms at 100 Hz.
