Impedence determination of a given mic

[rajaram04]

Hello sir

I want to know about the practical methods to determine impedence of any microphone no matter it is condencer type or dynamic one but i need very homely circuit arrangments for that . . please help

 

[FvM]

Seriously speaking, I don't see a particular need to measure microphone impedances because they are mostly well specified. But it's possible of course. The microphone output signal will be reduced to 50 percent if you load it with it's output impedance (impedance matching case).

For an accurate measurement, you'll use an audio frequency signal generator, a known series resistance, and an AC millivoltmeter or oscilloscope.

 

[rajaram04]

Seriously speaking, I don't see a particular need to measure microphone impedances because they are mostly well specified. But it's possible of course. The microphone output signal will be reduced to 50 percent if you load it with it's output impedance (impedance matching case).

For an accurate measurement, you'll use an audio frequency signal generator, a known series resistance, and an AC millivoltmeter or oscilloscope.

okk got it , so please what to do next after getting all these devices ????

 

[Audioguru]

A condenser mic needs an external 48V to bias its diaphragm. Maybe you have a more modern electret mic that is a condenser mic with the high voltage permanently set in its electret material and it has a built-in Jfet impedance reducer. Its impedance is about 3.3k ohms but the resistor that powers it is effectively in parallel so the total impedance is about 2.5k ohms.

A dynamic mic has a cone, coil and magnet like a little loudspeaker. Its impedance is from 150 ohms to 1200 ohms but is usually 600 ohms.

The output levels of different mic types are low and are about the same. They need a preamp.

 

[rajaram04]

A condenser mic needs an external 48V to bias its diaphragm. Maybe you have a more modern electret mic that is a condenser mic with the high voltage permanently set in its electret material and it has a built-in Jfet impedance reducer. Its impedance is about 3.3k ohms but the resistor that powers it is effectively in parallel so the total impedance is about 2.5k ohms.

A dynamic mic has a cone, coil and magnet like a little loudspeaker. Its impedance is from 150 ohms to 1200 ohms but is usually 600 ohms.

The output levels of different mic types are low and are about the same. They need a preamp.

ohh kk i see . . so recommend a good preamp.circuit of your own for such modern 600 ohms condencer mic please . . thanks for the info

 

[Audioguru]

Maybe instead of a condenser mic you have an electret mic that has 3 wires. Its output impedance is about 600 ohms because the output is from the source of the Jfet. The higher output impedance of a 2-wires electret mic is from the drain of the Jfet.

A preamp is simply a non-inverting audio opamp with a gain of about 200.
Here is one for a 2-wires electret mic:

 

[rajaram04]

Maybe instead of a condenser mic you have an electret mic that has 3 wires. Its output impedance is about 600 ohms because the output is from the source of the Jfet. The higher output impedance of a 2-wires electret mic is from the drain of the Jfet.

A preamp is simply a non-inverting audio opamp with a gain of about 200.
Here is one for a 2-wires electret mic:

ya i can understand & thanks for the diagram

& i have only 2 terminal condencer mic for now so i ve to work with itnself only

 

[Audioguru]

i have only 2 terminal condencer mic

No.
You probably have an electret mic./

 

[rajaram04]

No.
You probably have an electret mic./

ohh okk i see thats an electret one . . hmm