92Views6Replies

# tech noob question on stereo jack Answered

can I have a silly technical question for which I would have known the answer if I only paid more attention at school? how is possible that stereo headphones, ie 2 speaker circuits use only 3 cables? I understand the "ground" is the one that both speakers,ie left and right have in common but how come it doesnt bother the signals which go to the speakers? doesnt the left signal get mixed up with the right signal? and why is it called "ground" when it's not actually connected to the ground, like for example lightning conductor is? I've read through the wikipedia article about TRS several times but still can't understand it. thanks for answer, I promis I won't forget it this time :)

Tags:

## Discussions

The two signals are +ve relative to ground (which is common). GND is often actually connected to ground via the power supply. Rather like radio only has one wire as an aerial, the signal is between the one wire & the ground.

If both speakers have a common GND connection, they will run from two separate +ve signals.

L

Thanks! BTW, I love your soup cans :)

Best wishes for it (and thanks)

L

Thanks to all of you guys for explaining. Now I see it more clearly. Actually, when I try to imagine the circuit scheme in front of my eyes, it's pretty obvious. Since english is not my mother language, I was a bit confused about the "ground/negative/earth (walkman-connected-to-the-earth)" terminology, in my language it's quite messy as well which together, well, didn't work good for me :). Ok, I think I'll get some nice textbook for start.

To build on NachoMahma and lemonie's posts, there two main points you need to know.

- When we talk about voltage in a circuit what we're actually measuring is the voltage potential difference between to points in a circuit.

- In the circuit we define ground as zero volts at the negative termainal of the battery. This is our reference voltage that we will make other measurements relative to. (The fact that it's called ground is just a naming convention.)

By connecting the two speaker grounds together at the same point, we are forcing the voltage at the two wires to be the same (no resistance between the two points so, V = I*R = 0).   Now we can apply a different signal to the other end of each speaker, and because the speaker grounds are tied together we can get a different voltage across the two speakers when measured from ground.

I hope this helps clear it up a bit and is not confusing the issue more.  Like NachoMahma said, a rigorous explanation would require a physics textbook.

.  The fact that a TRS connector is used has nothing to do with it. Any 3-wire connector will work.
.  It's called ground because, in most "high" voltage (greater than 24 V or so) circuits and nearly all mains-supplied circuits, it is actually connected to Earth ground for safety reasons. In battery-powered equipment, it's just convention to call one side (usually negative) of the battery ground, even thought it may not be at ground potential.
.  As to why L and R don't interfere with each other: Lemonie's explanation is correct, but I'm not sure it will make much sense to a novice and I can't think of a better way to put it. hmmmm  The potential at the ground connection doesn't change with the signal. Does that help any?