Well, it's true that the bose system in these Audis are very odd. The fronts and rears *are* driven out of phase from the factory (with the Bose option, I believe {but haven't verified} the phase is reversed at the onboard amplifier).

When I installed my sub, I was very dissapointed until I reversed the phase (on the aftermarket sub) at the amplifier. The rear stock "sub" (if you can call it that; it's 4" I hear) and (I assume) rear door speakers were cancelling out a lot of the sound. I also noticed that adding a ~2ms delay to the sub's signal increased clarity and volume a bit more. Perhaps that's because I have my subs pointing backwards towards the rear of the trunk...

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