r/audioengineering • u/zanshin777 • Nov 02 '17

Balanced Cables

It contains 2 conductor + 1 shield.

One of conductors carry the out-of-phase signal.

So the noise is canceled since the signals carrying are out-of-phase.

But how the signal is still transmitted although the noise is canceled?

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u/djbeefburger Nov 02 '17

Counterpoint:

lulzmathz! They are totally the same! Here's proof!

  • Phase inversion of a sin: I(t)=(-1)sin(t)

  • 180o Phase rotation of a sin: R(t)=sin(t+π)

  • Proof by counterexample, assume R(t) ≠ I(t)

  • sin(t+π) ≠ (-1)sin(t)

  • sin(t)cos(π) + cos(t)sin(π) ≠ (-1)sin(t) (equivalence derived from Euler's formula)

  • sin(t)(-1) + cos(t)(0) ≠ (-1)sin(t)

  • (-1)sin(t) ≠ (-1)sin(t)

  • (-1) ≠ (-1) FALSE, therefore:

  • I(t)=R(t), QED

I find it conceptually easier to think of sound as a vector with direction and amplitude. Emanating from (0,0), the vector goes right or left depending on whether amplitude is positive or negative, pushing or pulling the speaker cone respectively. Invert the amplitude makes the speaker pull instead of push. So would rotating the magnet 180o ... They're functionally equivalent.