Ray
There is a phase checker sold in the US. THat would give you the right phase when correctly install
If you don't want to get the phase checker here is what you do, i recommend this as this is audio
Power everything up when in right or wrong phase both will work.
In the wrong phase
Soundstage is wide but there is no focus, and can sound thin
When in right phase
there is more focus and everything sounds better
CHeers
Nicholas