Doesn't matter whether car or house speaker, 8 or 4 ohm...whatever...out of phase implies that each channel given identical signals, one speaker will "pull" while the other will "push".

High-frequency signals are too fast to notice any phase difference. You need to feed a reasonably large woofer with a lot of power in order for it to push enough air to notice. The out-of-phase condition translates into a noticeable loss of bass response.

It's even audible with a couple of 6 x 9s...coupled to the trunk with a bit of wattage being fed to them, of course.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car