If you can handle a little math:

Let V = value of the input signal
Let P = balanced positive signal
Let N = balanced negative signal

The balance audio source splits the input signal (V) in half, and inverts the waveform of one of them.

P = (1/2 * V)
N = -(1/2 * V)

So if V = 10, P = 5 and N = -5
or P = -(N)

You send P and N along adjacent wires now, where they receive the same noise that bumps them up some.

P = 6 and N = -4
The balancing circuitry sees that P doesn't equal -(N) anymore, and knows that there was noise of value 1 introduced, and compensates, essentially deleting any noise that comes through. The difference between P and N is balanced.

Now, without differential balancing, you have the signal V and ground 0

So if V = 10 and Ground is a constant at 0, and you send them along the same wires and get that same noise:
V = 11. There's no balancing. The signal is now going to be different when it gets to the amplifier or speaker.

So why does this screw things up?

Well, if you send an unbalanced signal at the balanced amp, it sees:
P = 10, N = 0 and tries to eliminate 5 units of noise in the signal. If it did this absolutely perfectly, you would just be cutting the volume in half, but there's only so much the circuitry can do with that much "noise" so it ruins the audio signal and makes it much quieter.

 

Got it! So it's basically a form of noise reduction.

I'm assuming V, P, N, and S are all AC signals?

 

thnks to Top Teke and Wrathernaut. ive read countless of your posts over the last week. your knowledge is very valuable here on this forum. even considering you've probably heard these question many times over, you took the time to explain audio systems in a clear and concise manner. im now clear as to what i want and how to go about doing it. where do i send the six packs?

 

Well, even if I did drink, I'm in a country that forbids alcohol for another six months or so. Just help out others with similar questions, saves me from answering the same easy ones

 

ok. i take it youre military. if so, i wish you a safe return home.

 

Indeed.

I may die out here.
Of boredom.

Some jobs (the safe ones) are boring 99% of the time. That's where I am.

 

Thanks for thinking! Just have one (six-pack) for me and call it good, and ditto what Wrathernaut said.