Going on a bit of a rant here..
I have a few stereo amplifiers and even an audio mixer where the headphone outputs polarity is flipped 180 degrees. This is basically the equivalent of wiring positive to negative, and negative to positive, on both speakers, so that both left and right on headphones has its whole polarity flipped upside down. Not to confuse things but this is essentially what a Phase 0/180 switch does on a microphone preamp by flipping either positive>positive negative>negative (absolute phase), to positive>negative negative>positive (phase reverse, 180 degrees flip) on the input.
Here is what ticks me off... A lot of consumer audio equipment I found lately does not keep absolute polarity in mind, usually to cut costs in the design or lack of engineering care. Usually the saying is "No one will hear if the whole stereo waveform is upside down anyways". That may be true in 99% of cases... EXCEPT:
Try putting on headphones, singing into a microphone expecting the phase to be absolute throughout the audio chain. If this is the case then you will hear your voice normal in headphones and your voice leaking into the headphones will only add to the headphone sound. Now lets say somewhere in the audio chain the phase/polarity (same thing in this case) is flipped, you sing into the mic and loud breaths suck in the headphone diaphragm rather than push out, this causes subtraction from the leaking audio of your own voice into the headphones compared to the headphones themselves causing some weird shit to happen to your own voice in your head while hearing yourself.
The problem with this is that everyone wants to hear their voice naturally. If you are blowing out air into the mic your headphones should be pushing out into your ear, if you suck breath in, the headphone speakers should suck in. If you reverse this then no one thinks their voice sounds right in their cans and next thing you know the singer thinks either the mic is garbage or the mix is bad.
WHY DOES IT HAVE TO BE LIKE THIS? I am so annoyed right now because my stereo system that I use as a monitor doesn't give a shit about absolute phase, which forces me to use my microphone preamps phase invert button. This is fine, but then the waveform is upside down going into the computer, to make things even more strange the sound card in my computer... YES THE SOUND CARD manufacture didn't take absolute phase/polarity into mind when designing it, so negative peaks going into the computer look positive in software, and positive peaks going in look negative.
This shit is nuts and I am surprised it isn't discussed more! This may not be the right place so please point me to where I can bitch more about this lol. I wonder how many people think their mics sound awful in headphones because of this alone? That phase invert/flip button on a mic pre can make a HUGE difference while listening to yourself, even though in the recording while playing back you can rarely tell.