At right screen grabs from an INSTEK GDS 1022 digital oscilloscope showing the 180 degree difference summing of the output signals and the resulting doubling of voltage swing (+3dB).

At right screen grab the showing the summing of the output signals without phase reversal resulting in cancelling out. In use, this is how the balanced line treats hum and noise, which will be effectively 180 degrees out of phase after inversion.