Preamp inverts signal.

"Sidebar, how can I test my system for polarity? Test track?"

The most reliable way to test the system for absolute polarity is the in phase and out of phase tracks of the XLO Test CD. Of your system is in the correct absolute polarity the Out of Phase track will sound like it is coming at you from all around the room with no specific direction. And conversely the in phase track will sound like it's coming from dead center and be very focused. These effects are much more pronounced with proper speaker set up and after careful attention to room tuning. 

Geoff Kait

Geoffkait 03-20-2016 7:17am EDT
Of your system is in the correct absolute polarity the Out of Phase track will sound like it is coming at you from all around the room with no specific direction. And conversely the in phase track will sound like it’s coming from dead center and be very focused.

The description of "out of phase" in the first sentence is the effect of relative polarity being wrong, not absolute polarity being wrong. In other words, it is the effect of having the output of one speaker out of phase with respect to the output of the other speaker. Which would be the result of having + and - reversed in the connections to one speaker (but not both). The effects of incorrect absolute polarity (having the outputs of both speakers inverted, relative to the polarity that is presumed to have been received by the microphones during the recording session) are vastly more subtle, and may be imperceptible on most of the recordings that have a mix of different polarities for different instruments and singers.

Phd, thanks for the nice words.

Regards,
-- Al

My Croft 25R inverts but reversing speaker leads dulled the dynamics enough to be noticeable. I put them back to the way they are marked. I tried this with a number of recordings and results were consistent. 

Al, unfortunately phase and polarity are sometimes used interchangeably. In the case of the XLO test CD when they refer to "phase" they're actually referring to what we call absolute polarity now, you know, what with the book on polarity by Clark Johnsen and the work in the past ten years by George Louis.  Obviously one should not misconnect cables. If one speaker is out of phase due to miswiring the out of phase track will not sound correct.

cheers