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.
I also just tested this with a Stereophile Test CD (which bypasses the DAC), and the speakers definitely meet the test for being "in phase" though they are wired out of phase. (Disk 1 "The fender bass was recorded equally in each channel...")

My point is that everything was fine for years, and then suddenly I wasn’t hearing what I was used to. There is no evidence anybody changed anything in the system. It’s been this way a really long time.

I also just re-ran the Denon Audyssey room check, and now it’s telling me the Front Left is out of phase. And yet, the imaging is back to normal as if the speakers are actually in perfect phase.
There really is only one explanation for mysteriously reversing wires like this. If you want to avoid further problems I suggest you pay close attention to this video, lest the situation escalate.
:-)   Is that movie really worth watching???  I'm on the edge.

The trick here is that the wires really didn't get switched.  They were the same as always, but just started sounding out of phase.  Once I switched one speaker, that solved the case for sound.  But the speakers are now, technically, wired out of phase.

Hence my query of whether the phase signal could have been changed somewhere in the Denon or the Parasound amp?
There’s parts that are really, really well done. There’s parts that are heartfelt and inspirational. There’s parts that are basically fart jokes. Because it is after all a Will Farrell movie, so get real. The songs are the highlight. The opener is as good as anything from ABBA, and I actually like ABBA, and this is that quality, only funny. A lot of the songs have double meanings. Jaja Ding Dong seems like a funny Icelandic ditty until you catch "my love for you is growing wide and long" which if you think about it is pretty explicit, and the running joke about him being in love with his sister, Pierce Brosnan being a Lothario who fathered half the town. Also the contest political stuff is really well done, the banker pulling the strings, etc. So basically about half good gags, half good funny music, half potty humor. Typical Will Farrell, up there with Blades of Glory. (What do we have that the others don't? Matching junk? Right!) 

There’s simply no way any hardware caused a polarity switch in the speakers. Other than elves, I mean. But you do have a receiver, inside which all bets are off.

When properly set up the difference between in and out of phase will be more than just vocals being focused. When playing a mono track in phase everything should be coming right from the center. Nothing anywhere else. When playing out of phase the mono track should be coming from everywhere. Not only is nothing coming from the center, nothing is coming from anywhere. The sound is so diffuse there is nothing you can point to anywhere as the source of any of it, vocals, instruments, none of it. I forget the Stereophile CD but the XLO CD has a track recorded mono to do this test.

From what you’re saying its almost certain one channel did get reversed somewhere, some time. To track this down, follow the signal path. Plug earphones direct into the Mac mini. Then direct into the DAC. Use an adaptor, or sacrifice a cheap interconnect to get at the wires and hold them on your headphone plug. These connections only need to be good enough to hear if its in or out of phase. Which should be pretty obvious.

My bet is one of your three digital devices (I’m assuming the receiver includes a digital processor of some kind) messed up and needs a reboot. But mostly because otherwise we are back to the elves.
I am in the process of figuring out what s up with my 20 yr old Thors,, I just bought new Millennials tweeters, will arrive next week from Madisound,, Madisound just built new xovers with high quality parts,, but not sure if
A) recent mods bya  local tech on the Jadis DPL Linestage is the issue
B) the Millennials are going bad(just spend $100 for new voice  coils
C) the new xovers just are not as good as the old Hovalnd xovers.
So had all hooked up, and turned it on,, 
Disaster, Completely gone that gorgous Jadis sound, sounds like sh*t.   
Have 2 new Millennials on the way,, Tech guy wants me to swap out tweets BEFORE he chnages his mod back in the Jadis DPL to original design.. 
costing me $$$$$$$
I suggest you try new voice coils in the tweets.  They are  like $50 each. 

mozartfan, I think you posted in the wrong thread, but try hooking your speakers up out of phase to see if you get any interesting results!
Can hardware change speaker phasing over time??
theres no such thing as speaker phasing. The phase between left and right can switched anywhere along the signal chain. 
Maybe you changed it and hooked it up wrong by accident. Like you did it and forgot on day.The next day it was out of phase. We all forget sometime.
@ stroud27612
perhaps let's work through a troubleshooting procedure?
Your Denon receiver, is that your volume attenuation to your A21 amplifier?

Have you tried using another source? Like a CD player with it's own DAC for example?
Try switching to another source after you return the cables to your speakers in correct phase?
Did you reboot the computer?
Sorry, you may have done all of this already - I'm trying to help you get to the root cause, by a process of elimination.
@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.
Here we are, six months later, and last night I noticed I could hear and "see" each speaker again.  The vocals were not centered.

I wired the speakers back to "in phase" and the world was right again.  I have a wandering phase issue, either with one of the speakers or the electronics in the receiver or amp.
I wired the speakers back to "in phase" and the world was right again. I have a wandering phase issue, either with one of the speakers or the electronics in the receiver or amp.
I suggest you test your B&W CM10s polarity with a 1.5V battery, + to speaker positive and - to negative terminal and see if the woofers "pop" forward. But this test only determine the woofers polarity, in some cases, tweeter or/and mid-range driver could be wired out of phase to its woofers, due to some capacitors in series you need to check the tweeter and mid-range driver at its quick-connect terminals on the crossover.
Hey, what I think is going on more likely is you are training your own ear-brain mechanism.

It's like learning to read upside down.  For a while, you have to work at it, and then one day, bam, you can read upside down just fine, but you no longer can read normal directions of writing correctly. Same kind of thing has been tested with watching TV.

You are flipping the phase, your ear/brain mechanism is going "oh, look, something new!" and then one day your ear/brain gets used to it and that sensation is gone.
This may be completely unrelated and I know nothing about electronics but, I was an air conditioning tech for 40+ years. There is a weird thing that can happen on 480 volt ac units, if the capacitor for the outdoor fan motor goes bad, the fan will run backwards. Maybe you have a failed capacitor on the mid-range driver that is responsible for the problem. I have no idea if this is even feasible or not.
I understand the A/C capacitor issue.  When my capacitor went out, I could hear the unit trying to start, so I put a stick through the grill and gave the fan a push.  Sure enough it started running, though I had pushed it the wrong way!  The air was blowing down over the condenser, which still sorta worked.  Then the A/C guy came out and charged me $230 to replace the $12 capacitor.

As for training my ears, I had a lot of friends, at least one who is an audiophile with 5x more $$$ invested in this hobby than I have, and he heard the exact same thing.  Anyway, everything is back to normal.

Of course, as a hobbyist, I am now thinking of buying a new Lexicon receiver to replace the Denon.  It's just that damned urge to upgrade again.