Polarity inversion flips a speaker's waveform by 180° (push ↔ pull). It mirrors the signal, it does not delay it.
Normal vs inverted: leave everything Normal by default. Flip one box to Inverted when two sources that should add are instead cancelling, e.g. a sub wired out of phase, or the rear box of a cardioid array.
Phase interaction: two sources arriving in phase at a point add (up to +6 dB), constructive. Arriving exactly out of phase they cancel, destructive (a null). Inverting one source turns every add into a cancel and vice-versa.
Cardioid subs work by delaying and polarity-flipping a rear box so output cancels behind the array and reinforces in front.
Switch Display → Interference to see add (amber) and cancel (blue) zones, then toggle polarity to watch them swap.