@judsauce @quincy
Absolute phase.
Think of it this way -
If you have cone speakers and absolute phase is correct the drivers first inpetus is to push out and then back as the signal is applied.
If the absolute phase is reversed the cones first inpetus is to suck in instead of out when the first signal is applied.
When the absolute phase is correct with cone speakers I generally hear a more natural sound, when it is wrong I generally hear a slightly flattened soundstage, and at worst slight compression in the mids.
With electrostatics such as @lewm runs, his speakers, unlike most cone speakers, are pushing sound both frontwards and backwards so the effect is less apparent.
The problem with Conrad preamps is that most of them invert absolute phase in the line stage, so you simply reverse the + and - connections at the speaker.
However if you have a phono stage that inverts phase ( and the line stage does not ) then you can't reverse the + and - at the speaker because the CD or digital will then be out of absolute phase. In this case the best solution is to reverse the + and - connections on the cartridge for each channel.