“Most computer microphones use the third segment to carry bias power for the microphone.” https://en.wikipedia.org/wiki/Microphone_connector
I had thought it was to deliver sound to both sides (rather than left- or right-only) but here we are.
What is bias power?
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I have some headphones with a mic, but there is no bias voltage contact, only Left, Right, Mic(return?)and Ground. How does that work?
Most likely the mic is simply powered by the voltage which also powers the headphones.
But there’s also mics which don’t need voltage to work at all (unlikely for headsets tho).
Thankyou for asking this question, I have no clue and you’re making me think that a recent frontpanel audio TRRS jack board I designed might be wrong :D
There are two possible options I can see:
- There is no bias voltage and your mic works fine without it (ie it’s a dynamic mic or an electret mic without a jfet amplifier)
- The bias voltage is provided through the mic pin (via a resistor and/or inductor). The mic then overlays AC onto this DC signal.
I cannot find any good references or info about mic bias and TRRS connectors :( Anyone else have any luck? Wikipedia says it’s a standard referred to as “CTIA” or “AHJ” but those appear to be company names, not standard names.
My current headset uses a TRRS, but also provides an extension cable that splits into two 3.5mm TRS just like yours. I might probe it out and find out what it’s doing (but that doesn’t mean it’s the right/universal solution).
Some types of mic capsules require a voltage to work
As well as everyone else’s answer here about bias power: it could also just be because a 3-pin TRS are cheaper/easier to buy and get assembly tooling for than 2-pin TRS. Economies of scale.
(For a good example of this: 3-axis accelerometers are cheaper than 1-axis and 2-axis ones. Everyone wants 3-axis for mobile phones, drones, human inputs and the like. You’re better off buying a 3-axis chip and ignoring the extra channels)
LOL that’s not a stereo wire, that’s a headset combo jack.
I see two three pin 3.5mm stereo plugs (one of them color coded for the headphones and one for the mic), and zero 4-pin combo plugs?
No that is a stereo mic lead, hence the two rings.
I don’t think we can tell from just a picture of the plugs. These are definitely two 3.5mm stereo jacks, colored headphone and mic. Maybe have a look at the manual? Or type the model number into Google? Or use a multimeter and measure the resistance.
This was in a shop so yeah
What do you mean by stereo wire? It’s got 3 contacts on the 3.5mm jack, that’s enough to transfer analog stereo (GND, L, R).
Microphone is mono They’re wondering why there’s a third contact
It’s for bias to the mic. Condenser mics need it to apply bias to one of the leads of the mic so it can amplify the sound before sending it to the input of the card. Some mics don’t require that (self-biased) so in that case, the R pin (middle ring) goes to GND.
Ah, seems you’re right. I didn’t know that. But that seems to be an old way of doing it. I’ve only ever seen 2 contacts on a seperate microphone jack or the 4-contact combined ones in modern laptops.
The link doesn’t open, says connection refused 🤷.
Regardless, if it doesn’t require the bias pin, the mic is self-biased or biased through another source (use the same wire for the signal to get bias, this is easy, you just use a cap to decouple the signal from the bias).
So you have two low-quality mics that can distort your discord call twice as effective.
Innovation!
To my layman’s understanding (which is not good) it’s because of electronic resonance. In other words, how cables can give off/pick up radio waves.
In early radio, this was a problem with microphones picking up signal from radio transmissions, which obviously is unwanted when you’re trying to have people hear your voice, and not your voice mixed with competing radio signals.
From what I understand, when it comes to microphones, there is a “hot” a “ground” and a “cold”, and the cold is the same signal as the hot but inverted, and apparently this helps prevent picking up radio signals. It is called “balanced,” and I’m not sure why other than the inverted signals. So while it looks like a standard stereo cable with three connections, it’s apparently actually a standard microphone cable.
There’s a lot more radio/electric wizardry going on than that, but that’s my understanding of it, as a person who thinks Electricians are real life Wizards. This is based on some cursory internet research, so please anyone with more understanding correct me if I am wrong.
Is this better than a normal 4 contact jack without the cold?
“Cold” suggests you’re thinking of balanced signalling. You don’t have any balanced options with standard headphones and computer PC jacks, everything is unbalanced. Both the 4-connector (TRRS) and 2x3-connector (TRS) variants of your headphone connectors are unbalanced audio.
There might be a difference in crosstalk between the speaker and mic wires (ie signals going to your speakers leaking through the wire insulation and into the mic wires), but it should be inaudible if the cables and headset are designed correctly.
“Better” in terms of less radio interference? I suppose, probably.
I am not an audio engineer. It fascinates me, but most of it is beyond me.
Like how Apple used to be able to send video out of an iPod over a 1/8th connector, using the “sleeve” part as a 5th connector for video.
You’re describing balanced/differential signalling. This is used in stage or professional audio (typically over XLR connectors, but not always).
The 3.5mm TRS connectors that the OP has pictured are extremely unlikely to be using balanced signalling. If they did then they would not be compatible with the headphones jacks on computer motherboards or case fronts which follow the AC’97 or Intel HD Audio standards.
It has that wire to output audio on both speakers? That’s the green one btw. The pink is for mic input. USB could be for a few different things depending on the features that particularl set has.
Edit: Nvm, thought the question was for a headset, not a microphone. Unless the mic was part of a headset or something. Idk, other comments may have the answer.
The mic is part of the headset, I was wondering why there are 3 contacts on the mic wire unstead if 2 (signal,ground)
