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I recently learned that electricity doesn't actually flow from + to - but the other way around..

So my question would be: if I was using a 2 channel power amp and connected a speaker to it with the positive wire on the left channel (+) and the negative on the right channel (-) would I get the output of the left channel or the right channel?

I thought the (-) terminal on an amp was just to take the signal and ground it.

Timinycricket
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    That depends on the amplifier you use. It's worth mentioning that saying electricity doesn't flow from positive to negative isn't really all that helpful. _Electrons_ flow from negative to positive, sure, but since they have negative charge, the flow of charge is from positive to negative. Unless you're doing stuff at a very low level (like, looking at the physics of semiconductors) it's really easier to think about charge flowing from positive to negative than the other way around. – Hearth May 13 '18 at 21:15
  • Related: [What is it that strips vocals from audio when a 1/8" audio jack is partially unplugged?](https://electronics.stackexchange.com/q/42623/11683) – Dave Tweed May 13 '18 at 21:24
  • @Felthry. I believe they are called 'hole-carriers', acting as a transport for electrons which flow from atom to atom at the outer rings. The positive to negative notion is easier to wrap your brain around... –  May 13 '18 at 21:34
  • @Sparky256 ...sort of, but not exactly. Holes only exist in (p-type) semiconductors in any appreciable quantity; in metals they quickly recombine with electrons. – Hearth May 13 '18 at 22:06
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    _"I recently learned that electricity doesn't actually flow from + to - ..."_ - Electricity _does_ flow from **+** to **-**, because that's the way we defined electricity. Electrons flow the opposite direction, but that's irrelevant for most purposes. – marcelm May 13 '18 at 22:34

2 Answers2

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I recently learned that electricity doesn't actually flow from + to - but the other way around..

Keep that in the back of your mind but analyse circuits with current flowing from positive to negative. The convention was established before the discovery of the electron. The convention works and that's what we all use for normal circuit theory.

Audio is alternating voltage and current so + and - is just an indication to get the phase between speakers correct. If you weren't sure about a speaker you could connect a AA battery to its terminals and mark the terminals + and - if the cone pops out rather than in. If you then mark the speaker terminals you know which way to connect them to the amplifier. If you reverse the phase of one channel you will get cancellation in the middle of the stereo image.

So my question would be: if I was using a 2 channel power amp and connected a speaker to it with the positive wire on the left channel (+) and the negative on the right channel (-) would I get the output of the left channel or the right channel?

See below.

I thought the (-) terminal on an amp was just to take the signal and ground it.

It can be as shown in (a) below but not always.

schematic

simulate this circuit – Schematic created using CircuitLab

  • (a) A typical stereo amplifier with one side of each speaker grounded.
  • (b) A speaker connected to L+ and R- will sound the same as L+ to L- as the - terminals are connected internally. You will hear the left channel.
  • (c) Many amplifiers such as car audio systems use bridge-mode amplifiers to deliver more power from the low voltage supply. The + and - outputs are in anti-phase and neither is connected to ground.
  • (d) If you connect up your speaker L+ to R- on a bridged-mode amplifier you will get L+ - (-R-) = L+ + R-.

If you connect the speaker between L+ and R+ you will hear only the difference between the two channels. This will cut out all the sound in the centre of the stereo panorama - most noticably the bass and bass drum and probably the lead vocals.

Transistor
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  • I've seen some old amplifier designs that even had a transformer on the output to AC couple the audio. In that case, your channels would be isolated from each other, and you'd get no output at all. – Hearth May 13 '18 at 22:11
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The output you would get would represent the difference between the left and right channel. That is to say, if the outputs of your left and right channel were identical, you would get no output.

With speakers, there isn't truly a defined positive and negative terminal since they're essentially just electromagnets. Even though reversing the flow of current through an electromagnet changes the direction of magnetic force, the sound heard on a speaker corresponds to an oscillating magnetic force, so the current flowing through it will be varying in amplitude and possibly direction anyway (that is to say, there's no difference between push-and-pull and pull-and-push).

Billy Kalfus
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  • Actually, there's a huge difference, instantly recognizable by anyone who's ever wired the speakers of a stereo out of phase. Absolute phase has little, if any effect on our perception of the sound, but relative phase among multiple sources has large effects. – Dave Tweed May 13 '18 at 21:21
  • True. I suppose the point I was trying to make is that if you wanted, you could wire both speakers with the negative terminal connected to the signal and positive terminal connected to ground. As you said, it's the relative phase between them that is key. – Billy Kalfus May 13 '18 at 21:24
  • This isn't entirely true. This would be the case if you connected the negative of each channel together and the positive of the two channels to your speakers. But not if the connection between the two channels is undefined; if they're isolated you'll get no sound at all, for example. I doubt any audio amplifiers bother to have any substantial isolation, though. – Hearth May 13 '18 at 22:08
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    Brian Eno recommended an interesting 3 speaker setup for his Ambient 4 album, which fed the difference between the left and right channels to the rear speaker. http://music.hyperreal.org/artists/brian_eno/onland-txt.html – Dampmaskin May 13 '18 at 22:10