Can hardware change speaker phasing over time??


After years of great listening, I suddenly noticed I wasn't getting the sharp center image with vocals.  I spent hours moving the speakers and even did Room EQ on my Denon receiver (which normally would tell me if speakers are out of phase). The vocals sounded diffuse.  Finally, I switched the wires on one speaker.  BOOM!  Right back to crystal clear center imaging on vocals, on all of my favorite tracks.  I've checked all the wires.  Everything is hooked up right, though now red is hooked to black on one speaker.

Could something have changed the phasing in the hardware?  There is no other place in the set up the wires could have been reversed.  I have triple-checked that the ++++ cable is connected to the red output on the amp.  

Signal goes from Mac Mini by USB to Bryston DAC, by two single channel cables to Denon receiver, by two single channel cables to Parasound A21 Halo amp, by speaker wires (one wire marked ++++) to B&W CM10s.
stroud27612
@rixthetrick Very good ideas!   I tried this tonight.  I love that right now my living room floor is covered in wires and loose CDs, just like the old days, all in search of Truth!  (If only there were full ashtrays, empty wine bottles, and some young woman's unmentionables scattered in there, too.  Everything that made me love 2 channel!)

So I got an old dusty Playstation One out of the basement (Stereophile Magazine's #1 all time CD player) and plugged the right and left channels directly into my Parasound Amp.  So now we have bypassed the DAC and the Denon completely.  After adjusting the levels on the back of the Parasound, I played multiple Stereophile test disks phase check tracks (both Fender bass guitar and even dogs!), and they all sounded better and proper with the "out of phase" wiring instead of "in phase."  At this point, you are all rolling your eyes and saying one of his wires is crossed, but I have checked that many times.  I also played other CDs, including Rebecca Pidgeon, that normally produce great imaging, and they are all better after I rewired that one speaker.   It's interesting that the Denon, when included in the stream, still believes I have that one speaker out of phase, which I do if you just look at the speaker wires.

Anyway, I'm just going to put it all back to normal with the one speaker "out of phase", and keep grooving on some Nick Lowe and Cowboy Junkies.  So strange because the regular wiring worked for me for years, but suddenly we have this alternate sound that cannot be explained, but it can be fixed!
The mystery deepens! At lunch I hauled up my father’s old Mirage speakers and hooked them up to the full system, wired "in phase", and they sounded and tested as "in phase." So it has to be the B&W speakers.  I put the B&Ws back in the system, and they still only sound "in phase" if wired "out of phase."

Tonight I will hook them up to a different amp and see what happens.

And I have now created a special curse for B&W because you cannot use banana clips on them.
Listening to the CM10s wired "out of phase" was pleasant and produced good imaging with vocals and the Stereophile test tracks for phase.  But then I noticed I had lost a lot of bass on some songs.  Loss of bass is a side effect of being out of phase.  Wiring the speakers back in phase brought back the bass but lost the great vocal imaging.

So the only logical conclusion is that it's the tweeter or midrange driver on the one speaker that is out of phase from its counterpart.  I plan to test this hypothesis tonight with a bunch of test tones and see which ones sound focused and which ones sound diffused.