Headset mic not working

[flamer]

Hi experts,

I have a general aviation headset, the audio works well in both earcups, but the microphone is completely inoperable. Suspecting a bad solder joint, I pulled it all apart and did a continuity test from the plug that goes into the socket all the way through to the terminal on the microphone speaker and both sides look good (0.08 ohm resistance) I also tested resistance across the two terminals on the mic and it measures around 80ohm. My initial thought was the mic was stuffed, I did however wire the mic directly onto a 3.5mm plug and connect it to my pc, if i blew into the mic I could hear it, talking into it came out really garbled, I then did the same test with a known working headset (bare wires of the 3.5mm plug touched onto the headset jack) and it sounded exactly the same so now I am not sure it is the mic.

As I am running out of ideas, wondering if anyone has any suggestions on other tests I could do to see where the fault lies, also if anyone knows of a way I can properly test the mic so I can hear my voice clearly to completely rule it out without buying an expensive adaptor?

Also to note, this is a very cheap headset, it doesn't have any fancy noise cancellation and has a very basic circuit board which from what i can see just terminates the wires together. pic: https://imgur.com/a/tujtat4

thanks in advance!

 

[Tha fios agaibh]

Have you checked your sound settings on the computer?
There are advanced settings for recording devices /microphone which might not be set correctly.
Try turning off audio enhancements.

 

[flamer]

Hi thanks for your reply, yes I did try disable all sound enhancements, but still was not able to hear anything clearly - and that is the case with both my known working headset and the not working one.

I read this quote: "if you try to use a 300ohm headphone set with a standard pc sound card you may get no more sound than a whisper while a 32ohm headset would be deafening" - and then this: "Civilian systems use high-Z, 80-300Ω amplified electret Mics"

So I suspect using a PC will never work without amplification. I'm really starting to suspect the microphone isn't actually faulty its just the wrong type they have used (seems like it should be an electric microphone)

 

[Audioguru]

Your pc uses an electret mic that has an infinite resistance. When it is properly powered then it has an impedance that is 1k to 5k ohms.
An aviation mic might be an old fashioned carbon particles mic with a varying resistance or it might be a dynamic mic with a coil and magnet like an earphone or speaker.

The electret mic uses a low current and the carbon mic uses a much higher current. A dynamic mic must never be powered.

I think you connected an aviation carbon mic to your pc and it did not get enough current causing your voice to be garbled.

This does not make sense: "Civilian systems use high-Z, 80-300Ω amplified electret Mics". An electret mic is high impedance about 2000 to 5000 ohms. It has a Jfet in it that is powered to be an impedance converter, not as an amplifier. 80-300Ω is low-Z.

 

[flamer]

An aviation mic might be an old fashioned carbon particles mic with a varying resistance or it might be a dynamic mic with a coil and magnet like an earphone or speaker.

I think you connected an aviation carbon mic to your pc and it did not get enough current causing your voice to be garbled.

Yes I think you are on to it, the microphone appears to be just a tiny coil speaker, (if you check the image I posted in post 1 you can see it). I cant be sure whether it is carbon particle or dynamic but I am certain it is not electret.

I am wondering, should I just cut the mic out and replace it with a 2 pole electret mic? The higher end headphones all seem to have electret mics and the lower end have dynamic mics, will that work as a straight swap out or would an electret mic need extra components in the circuit to work correctly?

thanks!

 

[Audioguru]

Most electret mics have 2 terminals, the output that is powered with 0.5mA by the preamp, and the ground which connects to its metal case and to the cable's shield which connects to the preamp's ground. But electret mics are also available with 3 wires that you cannot use.

The original aviation mic is probably directional to reduce engine noise but most electret mics pickup sounds all around.

 

[flamer]

Thanks for that, so what do you reckon, as electret mic's are a lot easier to source and cheap, should I try a swap out? I found a very simple circuit setup that will can power an electric mic for outputting into a pc soundcard too.

Also, not that it matters much but I did find the spec sheet for this set of headphones:
Vocalism Principle: Dynamic
Sensitivity: 100±3dB
Resistance: 32Ω
Frequency Response Range: 20-20000Hz

thanks

 

[Audioguru]

The earphones are dynamic and are 32 ohms each. The microphone has no spec's.
The Frequency Response Range is absolutely useless since it does not say the plus and minus level deviation. Plus and minus 2dB is good but plus and minus 30dB is horrible.

A pc sound card mic input should already power an electret mic.